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Biondi, R., W. J. Randel, S. P. Ho, T. Neubert i S. Syndergaard. "Thermal structure of intense convective clouds derived from GPS radio occultations". Atmospheric Chemistry and Physics Discussions 11, nr 10 (27.10.2011): 29093–116. http://dx.doi.org/10.5194/acpd-11-29093-2011.
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Abstract. Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS occultations with CALIPSO profiles over deep convection. Results show a sharp spike in GPS bending angle highly correlated to the top of the clouds, corresponding to anomalously cold temperatures within the clouds. Above the clouds the temperatures return to background conditions, and there is a strong inversion at cloud top. For cloud tops below 14 km, the temperature lapse rate within the cloud often approaches a moist adiabat, consistent with rapid undiluted ascent within the convective systems.
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Biondi, R., W. J. Randel, S. P. Ho, T. Neubert i S. Syndergaard. "Thermal structure of intense convective clouds derived from GPS radio occultations". Atmospheric Chemistry and Physics 12, nr 12 (18.06.2012): 5309–18. http://dx.doi.org/10.5194/acp-12-5309-2012.
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Abstract. Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS occultations with CALIPSO profiles over deep convection. Results show a sharp spike in GPS bending angle highly correlated to the top of the clouds, corresponding to anomalously cold temperatures within the clouds. Above the clouds the temperatures return to background conditions, and there is a strong inversion at cloud top. For cloud tops below 14 km, the temperature lapse rate within the cloud often approaches a moist adiabat, consistent with rapid undiluted ascent within the convective systems.
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Kumar, Shailendra. "Vertical Characteristics of Reflectivity in Intense Convective Clouds using TRMM PR Data". Environment and Natural Resources Research 7, nr 2 (15.05.2017): 58. http://dx.doi.org/10.5539/enrr.v7n2p58.
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Tropical Rainfall Measuring Mission Precipitation Radar (TRMM-PR) based vertical structure in intense convective precipitation is presented here for Indian and Austral summer monsoon seasons. TRMM 2A23 data is used to identify the convective echoes in PR data. Two types of cloud cells are constructed here, namely intense convective cloud (ICC) and most intense convective cloud (MICC). ICC consists of PR radar beams having Ze>=40 dBZ above 1.5 km in convective precipitation area, whereas MICC, consists of maximum reflectivity at each altitude in convective precipitation area, with at least one radar pixel must be higher than 40 dBZ or more above 1.5 km within the selected areas. We have selected 20 locations across the tropics to see the regional differences in the vertical structure of convective clouds. One of the important findings of the present study is identical behavior in the average vertical profiles in intense convective precipitation in lower troposphere across the different areas. MICCs show the higher regional differences compared to ICCs between 5-12 km altitude. Land dominated areas show higher regional differences and Southeast south America (SESA) has the strongest vertical profile (higher Ze at higher altitude) followed by Indo-Gangetic plain (IGP), Africa, north Latin America whereas weakest vertical profile occurs over Australia. Overall SESA (41%) and IGP (36%) consist higher fraction of deep convective clouds (>10 km), whereas, among the tropical oceanic areas, Western (Eastern) equatorial Indian ocean consists higher fraction of low (high) level of convective clouds. Nearly identical average vertical profiles over the tropical oceanic areas, indicate the similarity in the development of intense convective clouds and useful while considering them in model studies.
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Hartung, Daniel C., Justin M. Sieglaff, Lee M. Cronce i Wayne F. Feltz. "An Intercomparison of UW Cloud-Top Cooling Rates with WSR-88D Radar Data". Weather and Forecasting 28, nr 2 (1.04.2013): 463–80. http://dx.doi.org/10.1175/waf-d-12-00021.1.
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Abstract The University of Wisconsin Convective Initiation (UWCI) algorithm utilizes geostationary IR satellite data to compute cloud-top cooling (UW-CTC) rates and assign CI nowcasts to vertically growing clouds. This study is motivated by National Weather Service (NWS) forecaster reviews of the algorithm output, which hypothesized that more intense cloud-top cooling corresponds to more vigorous short-term (0–60 min) convective development. An objective validation of UW-CTC rates using a satellite-based object-tracking methodology is presented, along with a prognostic evaluation of such cloud-top cooling rates for use in forecasting the growth and development of deep convection. In general, both a cloud object’s instantaneous and maximum cooling rate(s) are shown to be useful prognostic tools in predicting future radar intensification. UW-CTC rates are shown to be most skillful in detecting convective clouds that achieved intense radar signatures. The UW-CTC rate lead time ahead of the various radar fields is also shown, along with an illustration of the benefit of UW-CTC rates in operational forecasting. The results of this study suggest that convective clouds with the strongest UW-CTC rates are more likely to achieve significant near-term (0–60 min) radar signatures in such fields as composite reflectivity, vertically integrated liquid (VIL), and maximum estimated size of hail (MESH) compared to clouds that exhibit only weak UW-CTC rates.
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MOHANTY, U. C., N. V. SAM, S. DAS i S. BASU. "A study on the convective structure of the atmosphere over the West Coast of India during ARMEX-I". MAUSAM 56, nr 1 (19.01.2022): 49–58. http://dx.doi.org/10.54302/mausam.v56i1.857.
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Onset of south west monsoon (SWM) over Kerala is associated with intense convection followed by heavy rainfall over the west-coast of India. The intense rainfall events are usually associated with meso-scale convective systems embedded in large scale synoptic system over the Arabian Sea. Such deep and intense cumulus convection can have an important effect on the dynamics and energetics of large-scale atmospheric systems, because of the large magnitudes of the energy transformations associated with changes of phase of water in precipitating cumulus clouds as well as the strong updrafts and downdrafts in the troposphere.
The prime objective of this study is to understand the convective structure (active/suppressed) of the atmosphere over the west-coast of India during ARMEX-I (Arabian Sea Monsoon Experiment). This study uses an approach to obtain the average structure of a cloud cluster and its interaction with the environment that enables in distinguishing the variation of kinematic and convective parameters from suppressed to convectively active process. Upper air observations obtained from four coastal land stations viz., Bombay, Goa, Mangalore and Trivandrum, alongwith that obtained over ORV Sagar Kanya are used to calculate both the convective and the kinematic parameters at the centre of the polygon formed by these observation locations. Time averaged circulation kinematic parameters and vertical velocity during active and suppressed convective phases off the west coast of India were discussed. The apparent heating and the apparent moisture sink are also estimated through residuals of the thermodynamic equations during intense and weak phases of SWM.
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Kumar, Shailendra, i G. S. Bhat. "Vertical Profiles of Radar Reflectivity Factor in Intense Convective Clouds in the Tropics". Journal of Applied Meteorology and Climatology 55, nr 5 (maj 2016): 1277–86. http://dx.doi.org/10.1175/jamc-d-15-0110.1.
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AbstractThis study is based on the analysis of 10 years of data for radar reflectivity factor Ze as derived from the TRMM Precipitation Radar (PR) measurements. The vertical structure of active convective clouds at the PR pixel scale has been extracted by defining two types of convective cells. The first one is cumulonimbus tower (CbT), which contains Ze ≥ 20 dBZ at 12-km altitude and is at least 9 km deep. The other is intense convective cloud (ICC), which belongs to the top 5% of the population of the Ze distribution at a prescribed reference height. Here two reference heights (3 and 8 km) have been chosen. Regional differences in the vertical structure of convective cells have been explored by considering 16 locations distributed across the tropics and two locations in the subtropics. The choice of oceanic locations is based on the sea surface temperature; that of the land locations is based on propensity for intense convection. One of the main findings of the study is the close similarity in the average vertical profiles of CbTs and ICCs in the mid- and lower troposphere across the ocean basins whereas differences over land areas are larger and depend on the selected reference height. The foothills of the western Himalaya, southeastern South America, and the Indo-Gangetic Plain contain the most intense CbTs; equatorial Africa, the foothills of the western Himalaya, and equatorial South America contain the most intense ICCs. Close similarity among the oceanic profiles suggests that the development of vigorous convective cells over warm oceans is similar and that understanding gained in one region is extendable to other areas.
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Houze, Robert A. "Clouds in Tropical Cyclones". Monthly Weather Review 138, nr 2 (1.02.2010): 293–344. http://dx.doi.org/10.1175/2009mwr2989.1.
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Abstract Clouds within the inner regions of tropical cyclones are unlike those anywhere else in the atmosphere. Convective clouds contributing to cyclogenesis have rotational and deep intense updrafts but tend to have relatively weak downdrafts. Within the eyes of mature tropical cyclones, stratus clouds top a boundary layer capped by subsidence. An outward-sloping eyewall cloud is controlled by adjustment of the vortex toward gradient-wind balance, which is maintained by a slantwise current transporting boundary layer air upward in a nearly conditionally symmetric neutral state. This balance is intermittently upset by buoyancy arising from high-moist-static-energy air entering the base of the eyewall because of the radial influx of low-level air from the far environment, supergradient wind in the eyewall zone, and/or small-scale intense subvortices. The latter contain strong, erect updrafts. Graupel particles and large raindrops produced in the eyewall fall out relatively quickly while ice splinters left aloft surround the eyewall, and aggregates are advected radially outward and azimuthally up to 1.5 times around the cyclone before melting and falling as stratiform precipitation. Electrification of the eyewall cloud is controlled by its outward-sloping circulation. Outside the eyewall, a quasi-stationary principal rainband contains convective cells with overturning updrafts and two types of downdrafts, including a deep downdraft on the band’s inner edge. Transient secondary rainbands exhibit propagation characteristics of vortex Rossby waves. Rainbands can coalesce into a secondary eyewall separated from the primary eyewall by a moat that takes on the structure of an eye. Distant rainbands, outside the region dominated by vortex dynamics, consist of cumulonimbus clouds similar to non–tropical storm convection.
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Sieglaff, Justin M., Lee M. Cronce i Wayne F. Feltz. "Improving Satellite-Based Convective Cloud Growth Monitoring with Visible Optical Depth Retrievals". Journal of Applied Meteorology and Climatology 53, nr 2 (luty 2014): 506–20. http://dx.doi.org/10.1175/jamc-d-13-0139.1.
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AbstractThe use of geostationary satellites for monitoring the development of deep convective clouds has been recently well documented. One such approach, the University of Wisconsin Cloud-Top Cooling Rate (CTC) algorithm, utilizes frequent Geostationary Operational Environmental Satellite (GOES) observations to diagnose the vigor of developing convective clouds through monitoring cooling rates of infrared window brightness temperature imagery. The CTC algorithm was modified to include GOES visible optical depth retrievals for the purpose of identifying growing convective clouds in regions of thin cirrus clouds. An automated objective skill analysis of the two CTC versions (with and without the GOES visible optical depth) versus a variety of Next Generation Weather Radar (NEXRAD) fields was performed using a cloud-object tracking system developed at the University of Wisconsin Cooperative Institute for Meteorological Satellite Studies. The skill analysis was performed in a manner consistent with a recent study employing the same cloud-object tracking system. The analysis indicates that the inclusion of GOES visible optical depth retrievals in the CTC algorithm increases probability of detection and critical success index scores for all NEXRAD fields studied and slightly decreases false alarm ratios for most NEXRAD thresholds. In addition to better identifying vertically growing storms in regions of thin cirrus clouds, the analysis further demonstrates that the strongest cooling rates associated with developing convection are more reliably detected with the inclusion of visible optical depth and that storms that achieve intense reflectivity and large radar-estimated hail exhibit strong cloud-top cooling rates in much higher proportions than they do without the inclusion of visible optical depth.
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Liu, Jiachen, Jun Yang, Yixiao Zhang i Zhihong Tan. "Convection and Clouds under Different Planetary Gravities Simulated by a Small-domain Cloud-resolving Model". Astrophysical Journal 944, nr 1 (1.02.2023): 45. http://dx.doi.org/10.3847/1538-4357/aca965.
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Abstract In this study, we employ a cloud-resolving model to investigate how gravity influences convection and clouds in a small-domain (96 × 96 km) radiative–convective equilibrium. Our experiments are performed with a horizontal grid spacing of 1 km, which can resolve large (>1 km2) convective cells. We find that under a given stellar flux, sea surface temperature increases with decreasing gravity. This is because a lower-gravity planet has larger water vapor content and more clouds, resulting in a larger clear-sky greenhouse effect and a stronger cloud warming effect in the small domain. By increasing stellar flux under different gravity values, we find that the convection shifts from a quasi-steady state to an oscillatory state. In the oscillatory state, there are convection cycles with a period of several days, comprised of a short wet phase with intense surface precipitation and a dry phase with no surface precipitation. When convection shifts to the oscillatory state, the water vapor content and high-level cloud fraction increase substantially, resulting in rapid warming. After the transition to the oscillatory state, the cloud net positive radiative effect decreases with increasing stellar flux, which indicates a stabilizing climate effect. In the quasi-steady state, the atmospheric absorption features of CO2 are more detectable on lower-gravity planets because of their larger atmospheric heights. While in the oscillatory state, the high-level clouds mute almost all of the absorption features, making the atmospheric components hard to characterize.
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Rickenbach, Thomas, Paul Kucera, Megan Gentry, Larry Carey, Andrew Lare, Ruei-Fong Lin, Belay Demoz i David O’C Starr. "The Relationship between Anvil Clouds and Convective Cells: A Case Study in South Florida during CRYSTAL-FACE". Monthly Weather Review 136, nr 10 (październik 2008): 3917–32. http://dx.doi.org/10.1175/2008mwr2441.1.
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One of the important goals of NASA’s Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE) was to further the understanding of the evolution of tropical anvil clouds generated by deep convective systems. An important step toward understanding the radiative properties of convectively generated anvil clouds is to study their life cycle. Observations from ground-based radar, geostationary satellite radiometers, aircraft, and radiosondes during CRYSTAL-FACE provided a comprehensive look at the generation of anvil clouds by convective systems over South Florida during July 2002. This study focused on the relationship between convective rainfall and the evolution of the anvil cloud shield associated with convective systems over South Florida on 23 July 2002, during the CRYSTAL-FACE experiment. Anvil clouds emanating from convective cells grew downwind (to the southwest), reaching their maximum area at all temperature thresholds 1–2 h after the active convective cells collapsed. Radar reflectivity data revealed that precipitation-sized anvil particles extended downwind with the cloud tops. The time lag between maximum rainfall and maximum anvil cloud area increased with system size and rainfall. Observations from airborne radar and analysis of in situ cloud particle size distribution measurements in the anvil region suggested that gravitational size sorting of cloud particles dispersed downshear was a likely mechanism in the evolution of the anvil region. Linear regression analysis suggested a positive trend between this time lag and maximum convective rainfall for this case, as well as between the time lag and maximum system cloud cover. The injection of condensate into the anvil region by large areas of intense cells and dispersal in the upper-level winds was a likely explanation to cause the anvil cloud-top area to grow for 1–2 h after the surface convective rainfall began to weaken. In future work these relationships should be evaluated in differing regimes of shear, stability, or precipitation efficiency, such as over the tropical oceans, in order to generalize the results. The results of this study implied that for these cloud systems, the maximum in latent heating (proportional to rainfall) may precede the peak radiative forcing (related to anvil cloud height and area) by a lead time that was proportional to system size and strength. Mesoscale modeling simulations of convective systems on this day are under way to examine anvil evolution and growth mechanisms.
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Siqueira, Jose Ricardo, William B. Rossow, Luiz Augusto Toledo Machado i Cindy Pearl. "Structural Characteristics of Convective Systems over South America Related to Cold-Frontal Incursions". Monthly Weather Review 133, nr 5 (1.05.2005): 1045–64. http://dx.doi.org/10.1175/mwr2888.1.
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Abstract International Satellite Cloud Climatology Project (ISCCP DX) and microwave sensor data collected by the Tropical Rainfall Measuring Mission (TRMM) are used to identify and describe structural characteristics of convective systems (CSs) over continental South America (SA) related to cold-frontal incursions in a 3-yr period. An austral wet-season climatology for CS events of the three most important types of front–tropical convection interaction is built by applying latitude–time diagrams and a cloud-tracking method to DX data. Type 1 is characterized by the penetration of a cold front over subtropical SA that interacts with convection and moves with it into lower tropical latitudes. Type 2 refers to Amazon convection and its enhancement in a quasi-stationary northwest–southeast-oriented band extending from the Amazon to subtropical SA along with the passage of a cold front in the subtropics and characterizes the synoptic formation of the South Atlantic convergence zone. A quasi-stationary cold front over subtropical SA that has only weak interaction with tropical convection corresponds to type 3. Results show that the three types of front–tropical convection interaction strongly modulate deep convection over SA, producing mesoscale CSs with significant fractions of deep convective clouds and rain at their mature phase. Type 2 CSs (type 1 CSs) are constituted of larger deep convective cloud fractions with weaker (stronger) vertical development compared to type 1 CSs (type 3 CSs) in the Tropics (subtropics), resulting in larger rain fractions and less (more) presence of convective rain. Type 1 CSs have larger fractions of deep convective clouds and rain but with weaker vertical development in the subtropics than in the Tropics, showing that cold fronts organize convection more in area in the subtropics, but more in vertical extent in the Tropics. Life cycle variations of CS cloud and rain properties show tropical CSs with a more intense initial development and similar structural differences between the CS types and those found at their mature phase.
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Aumann, H. H., i S. G. DeSouza-Machado. "Deep convective clouds at the tropopause". Atmospheric Chemistry and Physics Discussions 10, nr 7 (2.07.2010): 16475–96. http://dx.doi.org/10.5194/acpd-10-16475-2010.
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Abstract. Data from the Advanced Infrared Sounder (AIRS) on the EOS Aqua spacecraft identify thousands of cloud tops colder than 225 K, loosely referred to as Deep Convective Clouds (DCC). Many of these cloud tops have "inverted" spectra, i.e. areas of strong water vapor, CO2 and ozone opacity, normally seen in absorption, are now seen in emission. We refer to these inverted spectra as DCCi. They are found in about 0.4% of all spectra from the tropical oceans excluding the Western Tropical Pacific (WTP), 1.1% in the WTP. The cold clouds are the anvils capping thunderstorms and consist of optically thick cirrus ice clouds. The precipitation rate associated with DCCi suggests that imbedded in these clouds, protruding above them, and not spatially resolved by the AIRS 15 km FOV, are even colder bubbles, where strong convection pushes clouds to within 5 hPa of the pressure level of the tropopause cold point. Associated with DCCi is a local upward displacement of the tropopause, a cold "bulge", which can be seen directly in the brightness temperatures of AIRS and AMSU channels with weighting function peaking between 40 and 2 hPa, without the need for a formal temperature retrieval. The bulge is not resolved by the analysis in numerical weather prediction models. The locally cold cloud tops relative to the analysis give the appearance (in the sense of an "illusion") of clouds overshooting the tropopause and penetrating into the stratosphere. Based on a simple model of optically thick cirrus clouds, the spectral inversions seen in the AIRS data do not require these clouds to penetrate into the stratosphere. However, the contents of the cold bulge may be left in the lower stratosphere as soon as the strong convection subsides. The heavy precipitation and the distortion of the temperature structure near the tropopause indicate that DCCi are associated with intense storms. Significant long-term trends in the statistical properties of DCCi could be interesting indicators of climate change.
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Vendrasco, Eder P., Luiz A. T. Machado, Bruno Z. Ribeiro, Edmilson D. Freitas, Rute C. Ferreira i Renato G. Negri. "Cloud-Resolving Model Applied to Nowcasting: An Evaluation of Radar Data Assimilation and Microphysics Parameterization". Weather and Forecasting 35, nr 6 (grudzień 2020): 2345–65. http://dx.doi.org/10.1175/waf-d-20-0017.1.
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AbstractThis research explores the benefits of radar data assimilation for short-range weather forecasts in southeastern Brazil using the Weather Research and Forecasting (WRF) Model’s three-dimensional variational data assimilation (3DVAR) system. Different data assimilation options are explored, including the cycling frequency, the number of outer loops, and the use of null-echo assimilation. Initially, four microphysics parameterizations are evaluated (Thompson, Morrison, WSM6, and WDM6). The Thompson parameterization produces the best results, while the other parameterizations generally overestimate the precipitation forecast, especially WDSM6. Additionally, the Thompson scheme tends to overestimate snow, while the Morrison scheme overestimates graupel. Regarding the data assimilation options, the results deteriorate and more spurious convection occurs when using a higher cycling frequency (i.e., 30 min instead of 60 min). The use of two outer loops produces worse precipitation forecasts than the use of one outer loop, and the null-echo assimilation is shown to be an effective way to suppress spurious convection. However, in some cases, the null-echo assimilation also removes convective clouds that are not observed by the radar and/or are still not producing rain, but have the potential to grow into an intense convective cloud with heavy rainfall. Finally, a cloud convective mask was implemented using ancillary satellite data to prevent null-echo assimilation from removing potential convective clouds. The mask was demonstrated to be beneficial in some circumstances, but it needs to be carefully evaluated in more cases to have a more robust conclusion regarding its use.
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Taylor, Christopher M., Cornelia Klein, Cheikh Dione, Douglas J. Parker, John Marsham, Cheikh Abdoulahat Diop, Jennifer Fletcher i in. "Nowcasting tracks of severe convective storms in West Africa from observations of land surface state". Environmental Research Letters 17, nr 3 (23.02.2022): 034016. http://dx.doi.org/10.1088/1748-9326/ac536d.
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Abstract In tropical convective climates, where numerical weather prediction of rainfall has high uncertainty, nowcasting provides essential alerts of extreme events several hours ahead. In principle, short-term prediction of intense convective storms could benefit from knowledge of the slowly evolving land surface state in regions where soil moisture controls surface fluxes. Here we explore how near-real time (NRT) satellite observations of the land surface and convective clouds can be combined to aid early warning of severe weather in the Sahel on time scales of up to 12 h. Using land surface temperature (LST) as a proxy for soil moisture deficit, we characterise the state of the surface energy balance in NRT. We identify the most convectively active parts of mesoscale convective systems (MCSs) from spatial filtering of cloud-top temperature imagery. We find that predictive skill provided by LST data is maximised early in the rainy season, when soils are drier and vegetation less developed. Land-based skill in predicting intense convection extends well beyond the afternoon, with strong positive correlations between daytime LST and MCS activity persisting as far as the following morning in more arid conditions. For a Forecasting Testbed event during September 2021, we developed a simple technique to translate LST data into NRT maps quantifying the likelihood of convection based solely on land state. We used these maps in combination with convective features to nowcast the tracks of existing MCSs, and predict likely new initiation locations. This is the first time to our knowledge that nowcasting tools based principally on land observations have been developed. The strong sensitivity of Sahelian MCSs to soil moisture, in combination with MCS life times of typically 6–18 h, opens up the opportunity for nowcasting of hazardous weather well beyond what is possible from atmospheric observations alone, and could be applied elsewhere in the semi-arid tropics.
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Friedrich, Katja, Evan A. Kalina, Joshua Aikins, David Gochis i Roy Rasmussen. "Precipitation and Cloud Structures of Intense Rain during the 2013 Great Colorado Flood". Journal of Hydrometeorology 17, nr 1 (17.12.2015): 27–52. http://dx.doi.org/10.1175/jhm-d-14-0157.1.
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Abstract Radar and disdrometer observations collected during the 2013 Great Colorado Flood are used to diagnose the spatial and vertical structure of clouds and precipitation during episodes of intense rainfall. The analysis focuses on 30 h of intense rainfall in the vicinity of Boulder, Colorado, during 2200–0400 UTC 11–13 September. The strongest rainfall occurred along lower parts of the Colorado Front Range at >1.6 km MSL and on the northern side of the Palmer Divide. The vertical structure of clouds and horizontal distribution of rainfall are strongly linked to upslope flow and low-level forcing, which resulted in surface convergence. During times of weak forcing, shallow convection produced rain at and below the melting layer through collision–coalescence and, to a lesser extent, riming. A mesoscale circulation interacting with the local terrain produced convective rainfall with high cloud tops that favored ice crystal production. During moderate forcing with cloud tops slightly exceeding the 0°C level, both cold- and warm-phase microphysical processes dominated. Less rain with weaker rainfall rates was observed over the higher-elevation stations compared to the lower-elevation stations across the foothills.
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Drofa, A. S., V. N. Ivanov, D. Rosenfeld i A. G. Shilin. "Studying an effect of salt powder seeding used for precipitation enhancement from convective clouds". Atmospheric Chemistry and Physics Discussions 10, nr 4 (23.04.2010): 10741–75. http://dx.doi.org/10.5194/acpd-10-10741-2010.
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Abstract. The experimental and theoretical studies of cloud microstructure modification with the "optimal" salt powder for obtaining additional precipitation amounts from convective clouds are performed. The results of experiments carried out in the cloud chamber at the conditions corresponding to the formation of convective clouds have shown that the introduction of the salt powder before a cloud medium is formed in the chamber results in the formation on the large-drop "tail" of additional large drops. In this case seeding with the salt powder leads to enlargement of the whole population of cloud drops and to a decrease of their total concentration as compared to the background cloud medium. These results are the positive factors for stimulating coagulation processes in clouds and for subsequent formation of precipitation in them. An overseeding effect, which is characterized by increased droplet concentration and decreased droplet size, was not observed even at high salt powder concentrations. The results of numerical simulations have shown that the transformation of cloud drop spectra induced by the introduction of the salt powder results in more intense coagulation processes in clouds as compared to the case of cloud modification with hygroscopic particles with relatively narrow particle size distributions, the South African hygroscopic particles from flares being an example of such distributions. The calculation results obtained with a one-dimensional model of a warm convective cloud demonstrated that the effect of salt powder on clouds (total amounts of additional precipitation) is significantly higher than the effect caused by the use of hygroscopic particles with narrow particle size distributions at comparable consumptions of seeding agents. Here we show that seeding at rather low consumption rate of the salt powder precipitation can be obtained from otherwise non precipitating warm convective clouds.
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Besson, L., i Y. Lemaître. "Mesoscale Convective Systems in Relation to African and Tropical Easterly Jets". Monthly Weather Review 142, nr 9 (wrzesień 2014): 3224–42. http://dx.doi.org/10.1175/mwr-d-13-00247.1.
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This paper documents the interaction processes between mesoscale convective systems (MCS), the tropical easterly jet (TEJ), and the African easterly jet (AEJ) over West Africa during the monsoon peak of 2006 observed during the African Monsoon Multidisciplinary Analyses (AMMA) project. The results highlight the importance of the cloud system localization relative to the jets in order to explain their duration and life cycle. A systematical study reveals that intense and long-lived MCSs correspond to a particular pattern where clouds associated with deep convection are located in entrance regions of TEJ and in exit regions of AEJ. A case study on a particularly well-documented convective event characterizes this link and infers the importance of jet streaks in promoting areas of divergence, favoring the persistence of MCSs.
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Wapler, Kathrin, Todd P. Lane, Peter T. May, Christian Jakob, Michael J. Manton i Steven T. Siems. "Cloud-System-Resolving Model Simulations of Tropical Cloud Systems Observed during the Tropical Warm Pool-International Cloud Experiment". Monthly Weather Review 138, nr 1 (1.01.2010): 55–73. http://dx.doi.org/10.1175/2009mwr2993.1.
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Abstract Nested cloud-system-resolving model simulations of tropical convective clouds observed during the recent Tropical Warm Pool-International Cloud Experiment (TWP-ICE) are conducted using the Weather Research and Forecasting (WRF) model. The WRF model is configured with a highest-resolving domain that uses 1.3-km grid spacing and is centered over Darwin, Australia. The performance of the model in simulating two different convective regimes observed during TWP-ICE is considered. The first regime is characteristic of the active monsoon, which features widespread cloud cover that is similar to maritime convection. The second regime is a monsoon break, which contains intense localized systems that are representative of diurnally forced continental convection. Many aspects of the model performance are considered, including their sensitivity to physical parameterizations and initialization time, and the spatial statistics of rainfall accumulations and the rain-rate distribution. While the simulations highlight many challenges and difficulties in correctly modeling the convection in the two regimes, they show that provided the mesoscale environment is adequately reproduced by the model, the statistics of the simulated rainfall agrees reasonably well with the observations.
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Oertel, Annika, Michael Sprenger, Hanna Joos, Maxi Boettcher, Heike Konow, Martin Hagen i Heini Wernli. "Observations and simulation of intense convection embedded in a warm conveyor belt – how ambient vertical wind shear determines the dynamical impact". Weather and Climate Dynamics 2, nr 1 (2.02.2021): 89–110. http://dx.doi.org/10.5194/wcd-2-89-2021.
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Abstract. Warm conveyor belts (WCBs) are dynamically important, strongly ascending and mostly stratiform cloud-forming airstreams in extratropical cyclones. Despite the predominantly stratiform character of the WCB's large-scale cloud band, convective clouds can be embedded in it. This embedded convection leads to a heterogeneously structured cloud band with locally enhanced hydrometeor content, intense surface precipitation and substantial amounts of graupel in the middle troposphere. Recent studies showed that embedded convection forms dynamically relevant quasi-horizontal potential vorticity (PV) dipoles in the upper troposphere. Thereby one pole can reach strongly negative PV values associated with inertial or symmetric instability near the upper-level PV waveguide, where it can interact with and modify the upper-level jet. This study analyzes the characteristics of embedded convection in the WCB of cyclone Sanchez based on WCB online trajectories from a convection-permitting simulation and airborne radar observations during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) field campaign (intense observation periods, IOPs, 10 and 11). In the first part, we present the radar reflectivity structure of the WCB and corroborate its heterogeneous cloud structure and the occurrence of embedded convection. Radar observations in three different sub-regions of the WCB cloud band reveal the differing intensity of its embedded convection, which is qualitatively confirmed by the ascent rates of the online WCB trajectories. The detailed ascent behavior of the WCB trajectories reveals that very intense convection with ascent rates of 600 hPa in 30–60 min occurs, in addition to comparatively moderate convection with slower ascent velocities as reported in previous case studies. In the second part of this study, a systematic Lagrangian composite analysis based on online trajectories for two sub-categories of WCB-embedded convection – moderate and intense convection – is performed. Composites of the cloud and precipitation structure confirm the large influence of embedded convection: intense convection produces very intense local surface precipitation with peak values exceeding 6 mm in 15 min and large amounts of graupel of up to 2.8 g kg−1 in the middle troposphere (compared to 3.9 mm and 1.0 g kg−1 for the moderate convective WCB sub-category). In the upper troposphere, both convective WCB trajectory sub-categories form a small-scale and weak PV dipole, with one pole reaching weakly negative PV values. However, for this WCB case study – in contrast to previous case studies reporting convective PV dipoles in the WCB ascent region with the negative PV pole near the upper-level jet – the negative PV pole is located east of the convective ascent region, i.e., away from the upper-level jet. Moreover, the PV dipole formed by the intense convective WCB trajectories is weaker and has a smaller horizontal and vertical extent compared to a previous NAWDEX case study of WCB-embedded convection, despite faster ascent rates in this case. The absence of a strong upper-level jet and the weak vertical shear of the ambient wind in cyclone Sanchez are accountable for the weak diabatic PV modification in the upper troposphere. This implies that the strength of embedded convection alone is not a reliable measure for the effect of embedded convection on upper-level PV modification and its impact on the upper-level jet. Instead, the profile of vertical wind shear and the alignment of embedded convection with a strong upper-level jet play a key role for the formation of coherent negative PV features near the jet. Finally, these results highlight the large case-to-case variability of embedded convection not only in terms of frequency and intensity of embedded convection in WCBs but also in terms of its dynamical implications.
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Lau, William K. M., Kyu-Myong Kim, Jiun-Dar Chern, W. K. Tao i L. Ruby Leung. "Structural changes and variability of the ITCZ induced by radiation–cloud–convection–circulation interactions: inferences from the Goddard Multi-scale Modeling Framework (GMMF) experiments". Climate Dynamics 54, nr 1-2 (5.10.2019): 211–29. http://dx.doi.org/10.1007/s00382-019-05000-y.
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Abstract In this paper, we have investigated the impact of radiation–cloud–convection–circulation interaction (RC3I) on structural changes and variability of the Inter-tropical Convergence Zone (ITCZ) using the Goddard Multi-scale Modeling Framework, where cloud processes are super-parameterized, i.e., explicitly resolved with 2-D cloud resolving models embedded in each coarse grid of the host Goddard Earth Observing System-Version 5 global climate model. Experiments have been conducted under prescribed sea surface temperature conditions for 10 years (2007–2016), with and without cloud radiation feedback in the atmosphere, respectively. Diagnostic analyses separately for January and July show that RC3I leads to an enhanced and expanded Hadley Circulation characterized by (1) a quasi-uniform warming and moistening of the tropical atmosphere and a sharpening of the ITCZ with enhanced deep convection, more intense precipitation and higher clouds, (2) extended drying of the tropical marginal convective zones, and extratropical mid- to lower troposphere, and (3) a cooling of the polar regions, with increased baroclinicity and midlatitude storm track activities. Computations based on the zonal mean thermodynamic energy balance equation show that the radiative warming and cooling are strongly balanced by local adiabatic processes associated with changes in large-scale vertical motions, as well as horizontal atmospheric heat transport. In the tropics, enhanced short-wave absorption and longwave water vapor greenhouse effects by high clouds play key roles in providing strong positive feedback to the tropospheric warming. In the extratropics, increased atmospheric heat transport associated with changes in the Hadley circulation is balanced by strong longwave cooling above, and warming below due to increased high clouds. We also find a strong positive correlation between daily and pentad heavy rain in the ITCZ core, and expansion of the drier zones coupled to a contraction of the highly convective zones in the ITCZ, indicating a strong tendency RC3I-induced convective aggregation in tropical clouds i.e., wet-regions-get-wetter and contracted, and dry-areas-get-drier and expanded.
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Varble, Adam C., Stephen W. Nesbitt, Paola Salio, Joseph C. Hardin, Nitin Bharadwaj, Paloma Borque, Paul J. DeMott i in. "Utilizing a Storm-Generating Hotspot to Study Convective Cloud Transitions: The CACTI Experiment". Bulletin of the American Meteorological Society 102, nr 8 (sierpień 2021): E1597—E1620. http://dx.doi.org/10.1175/bams-d-20-0030.1.
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AbstractThe Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to improve understanding of orographic cloud life cycles in relation to surrounding atmospheric thermodynamic, flow, and aerosol conditions. The deployment to the Sierras de Córdoba range in north-central Argentina was chosen because of very frequent cumulus congestus, deep convection initiation, and mesoscale convective organization uniquely observable from a fixed site. The C-band Scanning Atmospheric Radiation Measurement (ARM) Precipitation Radar was deployed for the first time with over 50 ARM Mobile Facility atmospheric state, surface, aerosol, radiation, cloud, and precipitation instruments between October 2018 and April 2019. An intensive observing period (IOP) coincident with the RELAMPAGO field campaign was held between 1 November and 15 December during which 22 flights were performed by the ARM Gulfstream-1 aircraft. A multitude of atmospheric processes and cloud conditions were observed over the 7-month campaign, including numerous orographic cumulus and stratocumulus events; new particle formation and growth producing high aerosol concentrations; drizzle formation in fog and shallow liquid clouds; very low aerosol conditions following wet deposition in heavy rainfall; initiation of ice in congestus clouds across a range of temperatures; extreme deep convection reaching 21-km altitudes; and organization of intense, hail-containing supercells and mesoscale convective systems. These comprehensive datasets include many of the first ever collected in this region and provide new opportunities to study orographic cloud evolution and interactions with meteorological conditions, aerosols, surface conditions, and radiation in mountainous terrain.
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Drofa, A. S., V. N. Ivanov, D. Rosenfeld i A. G. Shilin. "Studying an effect of salt powder seeding used for precipitation enhancement from convective clouds". Atmospheric Chemistry and Physics 10, nr 16 (27.08.2010): 8011–23. http://dx.doi.org/10.5194/acp-10-8011-2010.
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Abstract. Experimental and theoretical studies of cloud microstructure modification with hygroscopic particles for obtaining additional precipitation amounts from convective clouds are performed. The experiment used salt powder with the particle sizes that gave the greatest effectiveness according to the simulations of Segal et al. (2004). The experiments were carried out in a cloud chamber at the conditions corresponding to the formation of convective clouds. The results have shown that the introduction of the salt powder before a cloud medium is formed in the chamber results in the formation on a "tail" of additional large drops. In this case seeding with the salt powder leads also to enlargement of the whole population of cloud drops and to a decrease of their total concentration as compared to a cloud medium that is formed on background aerosols. These results are the positive factors for stimulating coagulation processes in clouds and for subsequent formation of precipitation in them. An overseeding effect, which is characterized by increased droplet concentration and decreased droplet size, was not observed even at high salt powder concentrations. The results of numerical simulations have shown that the transformation of cloud drop spectra induced by the introduction of the salt powder results in more intense coagulation processes in clouds as compared to the case of cloud modification with hygroscopic particles with relatively narrow particle size distributions, and for the distribution of the South African hygroscopic flares. The calculation results obtained with a one-dimensional model of a warm convective cloud demonstrated that the effect of salt powder on clouds (total amounts of additional precipitation) is significantly higher than the effect caused by the use of hygroscopic particles with narrow particle size distributions at comparable consumptions of seeding agents, or with respect to the hygroscopic flares. Here we show that seeding at rather low consumption rate of the salt powder initiates precipitation from otherwise non precipitating warm convective clouds, mainly by the effect of adding large cloud drops to the tail of the distribution.
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Zelinka, Mark D., i Dennis L. Hartmann. "Response of Humidity and Clouds to Tropical Deep Convection". Journal of Climate 22, nr 9 (1.05.2009): 2389–404. http://dx.doi.org/10.1175/2008jcli2452.1.
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Abstract Currently available satellite data can be used to track the response of clouds and humidity to intense precipitation events. A compositing technique centered in space and time on locations experiencing high rain rates is used to detail the characteristic evolution of several quantities measured from a suite of satellite instruments. Intense precipitation events in the convective tropics are preceded by an increase in low-level humidity. Optically thick cold clouds accompany the precipitation burst, which is followed by the development of spreading upper-level anvil clouds and an increase in upper-tropospheric humidity over a broader region than that occupied by the precipitation anomalies. The temporal separation between the convective event and the development of anvil clouds is about 3 h. The humidity increase at upper levels and the associated decrease in clear-sky longwave emission persist for many hours after the convective event. Large-scale vertical motions from reanalysis show a coherent evolution associated with precipitation events identified in an independent dataset: precipitation events begin with stronger upward motion anomalies in the lower troposphere, which then evolve toward stronger upward motion anomalies in the upper troposphere, in conjunction with the development of anvil clouds. Greater upper-tropospheric moistening and cloudiness are associated with larger-scale and better-organized convective systems, but even weaker, more isolated systems produce sustained upper-level humidity and clear-sky outgoing longwave radiation anomalies.
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Lei, Siliang, Xijuan Zhu, Yuxiang Ling, Shiwen Teng i Bin Yao. "Tropical Tropopause Layer Cloud Properties from Spaceborne Active Observations". Remote Sensing 15, nr 5 (22.02.2023): 1223. http://dx.doi.org/10.3390/rs15051223.
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A significant part of clouds in the tropics appears over the tropopause due to intense convections and in situ condensation activity. These tropical tropopause layer (TTL) clouds not only play an important role in the radiation budget over the tropics, but also in water vapor and other chemical material transport from the troposphere to the stratosphere. This study quantifies and analyzes the properties of TTL clouds based on spaceborne active observations, which provide one of the most reliable sources of information on cloud vertical distributions. We use four years (2007–2010) of observations from the joint Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat and consider all cloudy pixels with top height above the tropopause as TTL clouds. The occurrence frequency of TTL clouds during the nighttime is found to be almost 13% and can reach ~50–60% in areas with frequent convections. The annual averages of tropical tropopause height, tropopause temperature, and cloud top height are 16.2 km, −80.7 °C, and 16.6 km, respectively, and the average cloud top exceeds tropopause by approximately 500 m. More importantly, the presence of TTL clouds causes tropopause temperature to be ~3–4 °C colder than in the all-sky condition. It also lifts the tropopause heights ~160 m during the nighttime and lowers the heights ~84 m during the daytime. From a cloud type aspect, ~91% and ~4% of the TTL clouds are high clouds and altostratus, and only ~5% of them are associated with convections (i.e., nimbostratus and deep convective clouds). Approximately 30% of the TTL clouds are single-layer clouds, and multi-layer clouds are dominated by those with 2–3 separated layers.
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Kodama, Yasu-Masa, Haruna Okabe, Yukie Tomisaka, Katsuya Kotono, Yoshimi Kondo i Hideyuki Kasuya. "Lightning Frequency and Microphysical Properties of Precipitating Clouds over the Western North Pacific during Winter as Derived from TRMM Multisensor Observations". Monthly Weather Review 135, nr 6 (1.06.2007): 2226–41. http://dx.doi.org/10.1175/mwr3388.1.
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Abstract Tropical Rainfall Measuring Mission observations from multiple sensors including precipitation radar, microwave and infrared radiometers, and a lightning sensor were used to describe precipitation, lightning frequency, and microphysical properties of precipitating clouds over the midlatitude ocean. Precipitation over midlatitude oceans was intense during winter and was often accompanied by frequent lightning. Case studies over the western North Pacific from January and February 2000 showed that some lightning occurred in deep precipitating clouds that developed around cyclones and their attendant fronts. Lightning also occurred in convective clouds that developed in regions of large-scale subsidence behind extratropical cyclones where cold polar air masses were strongly heated and moistened from below by the ocean. The relationships between lightning frequency and the minimum polarization corrected temperature (PCT) at 37 and 85 GHz and the profile of the maximum radar reflectivity resembled relationships derived previously for cases in the Tropics. Smaller lapse rates in the maximum radar reflectivity above the melting level indicate vigorous convection that, although shallow and relatively rare, was as strong as convection over tropical oceans. Lightning was most frequent in systems for which the minimum PCT at 37 GHz was less than 260 K. Lightning and PCT at 85 GHz were not as well correlated as lightning and PCT at 37 GHz. Thus, lightning was frequent in convective clouds that contained many large hydrometeors in the mixed-phase layer, because PCT is more sensitive to large hydrometeors at 37 than at 85 GHz. The relationship between lightning occurrence and cloud-top heights derived from infrared observations was not straightforward. Microphysical conditions that support lightning over the midlatitude ocean in winter were similar to conditions in the Tropics and are consistent with Takahashi’s theory of riming electrification.
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Zhou, Y. P., W. K. Tao, A. Y. Hou, W. S. Olson, C. L. Shie, K. M. Lau, M. D. Chou, X. Lin i M. Grecu. "Use of High-Resolution Satellite Observations to Evaluate Cloud and Precipitation Statistics from Cloud-Resolving Model Simulations. Part I: South China Sea Monsoon Experiment". Journal of the Atmospheric Sciences 64, nr 12 (1.12.2007): 4309–29. http://dx.doi.org/10.1175/2007jas2281.1.
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Abstract Cloud and precipitation simulated using the three-dimensional (3D) Goddard Cumulus Ensemble (GCE) model are compared to Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Precipitation Radar (PR) rainfall measurements and Clouds and the Earth’s Radiant Energy System (CERES) single scanner footprint (SSF) radiation and cloud retrievals. Both the model simulation and retrieved parameters are based upon observations made during the South China Sea Monsoon Experiment (SCSMEX) field campaign. The model-simulated cloud and rain systems are evaluated by systematically examining important parameters such as the surface rain rate, convective/stratiform percentage, rain profiles, cloud properties, and precipitation efficiency. It is demonstrated that the GCE model is capable of simulating major convective system development and reproduces the total surface rainfall amount as compared to rainfall estimated from the SCSMEX sounding network. The model yields a slightly higher total convective rain/stratiform rain ratio than the TMI and PR observations. The GCE rainfall spectrum exhibits a greater contribution from heavy rains than those estimated from PR or TMI observations. In addition, the GCE simulation produces much greater amounts of snow and graupel than the TRMM retrievals. The model’s precipitation efficiency of convective rain is close to the observations, but the precipitation efficiency of stratiform rain is much lower than the observations because of large amounts of slowly falling simulated snow and graupel. Compared to observations, the GCE produces more compact areas of intense convection and less anvil cloud, which are consistent with a smaller total cloud fraction and larger domain-averaged outgoing longwave radiation.
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Riley, Emily M., Brian E. Mapes i Stefan N. Tulich. "Clouds Associated with the Madden–Julian Oscillation: A New Perspective from CloudSat". Journal of the Atmospheric Sciences 68, nr 12 (1.12.2011): 3032–51. http://dx.doi.org/10.1175/jas-d-11-030.1.
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Abstract The evolution of total cloud cover and cloud types is composited across the Madden–Julian oscillation (MJO) using CloudSat data for June 2006–May 2010. Two approaches are used to define MJO phases: 1) the local phase is determined at each longitude and time from filtered outgoing longwave radiation, and 2) the global phase is defined using a popular real-time multivariate MJO (RMM) index, which assigns the tropics to an MJO phase each day. In terms of local phase, CloudSat results show a familiar evolution of cloud type predominance: in the growing stages shallow clouds coexist with deep, intense, but narrow convective systems. Widespread cloud coverage and rainfall appear during the active phases, becoming more anvil dominated with time, and finally suppressed conditions return. Results are compared to the convectively coupled Kelvin wave, which has a similar life cycle to the MJO. Convection in the MJO tends to be modulated more by moisture variations compared to the Kelvin wave. In terms of global phases, wide deep precipitating, anvil, cumulus congestus, and altocumulus types exhibit similar eastward propagation from the Indian Ocean to the central Pacific, while the narrow deep precipitating type only propagates to the Maritime Continent. These propagating types also show coherent Western Hemisphere signals. Generally, negative Western Hemisphere anomalies occur when anomalies are positive over the Indian Ocean. In both approaches, sampling leads to pictorial renderings of actual clouds across MJO phases. These mosaics provide an objective representation of the cloud field that was unavailable before CloudSat and serve as a reminder to the complex nature of the MJO’s multiscale features.
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Wall, Christina, Edward Zipser i Chuntao Liu. "An Investigation of the Aerosol Indirect Effect on Convective Intensity Using Satellite Observations". Journal of the Atmospheric Sciences 71, nr 1 (27.12.2013): 430–47. http://dx.doi.org/10.1175/jas-d-13-0158.1.
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Abstract The effect of the environment on individual clouds makes it difficult to isolate the signal of the aerosol indirect effect, particularly at larger spatial and temporal scales. This study uses observations from the Tropical Rainfall Measuring Mission (TRMM), CloudSat, and Aqua satellites to identify convective cloud systems in clean and dirty environments. The Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol index is collocated with radar precipitation features (RPFs) from TRMM and congestus cloud features (CFs) from CloudSat. The Interim ECMWF Re-Analysis (ERA-Interim) is interpolated to identify the environmental profile surrounding each feature. Regions in Africa, the Amazon, the Atlantic Ocean, and the southwestern United States are examined. TRMM features in the Africa and Amazon regions are more intense and have higher lightning flash rates under dirty background conditions. RPFs in the southwestern United States are more intense under clean background conditions. The Atlantic region shows little difference in intensity. The differences found in the mean thermodynamic profile for RPFs forming in clean and dirty environments could explain these differences in convective intensity. Congestus identified with CloudSat show smaller differences between clouds forming in clean and dirty environments in Africa and the Amazon. Congestus in clean environments have higher reflectivities and generally larger widths, but no trend is seen in cloud-top height. The signal of the aerosol indirect effect is so small that it is very difficult to detect confidently using these methods. The environment must be considered in any study of the aerosol indirect effect, because important environmental changes can occur as aerosols are introduced to an air mass.
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Yusnaini, Helmi, i Marzuki . "Vertical Distribution of Radar Reflectivity Factor in Intense Convective Clouds over Indonesia". KnE Engineering 1, nr 2 (16.04.2019): 141. http://dx.doi.org/10.18502/keg.v1i2.4439.
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Yusnaini, H., i Marzuki. "Diurnal variation of radar reflectivity factor during intense convective clouds over Indonesia". Journal of Physics: Conference Series 1528 (kwiecień 2020): 012024. http://dx.doi.org/10.1088/1742-6596/1528/1/012024.
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Zhang, Sidou, Shiyin Liu i Tengfei Zhang. "Analysis on the Evolution and Microphysical Characteristics of Two Consecutive Hailstorms in Spring in Yunnan, China". Atmosphere 12, nr 1 (2.01.2021): 63. http://dx.doi.org/10.3390/atmos12010063.
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By using products of the cloud model, National Centers for Environmental Prediction (NCEP) Final Operational Global Analysis (FNL) reanalysis data, and Doppler weather radar data, the mesoscale characteristics, microphysical structure, and mechanism of two hail cloud systems which occurred successively within 24 h in southeastern Yunnan have been analyzed. The results show that under the influence of two southwest jets in front of the south branch trough (SBT) and the periphery of the western Pacific subtropical high (WPSH), the northeast-southwest banded echoes affect the southeastern Yunnan of China twice. Meanwhile, the local mesoscale radial wind convergence and uneven wind speed lead to the intense development of convective echoes and the occurrence of hail. The simulated convective cloud bands are similar to the observation. The high-level mesoscale convergence line leads to the development of convective cloud bands. The low-level wind direction or wind speed convergence and the high-level wind speed divergence form a deep tilted updraft, with the maximum velocity of 15 m·s−1 at the −40~−10 °C layer, resulting in the intense development of local convective clouds. The hail embryos form through the conversion or collision growth of cloud water and snowflakes and have little to do with rain and ice crystals. Abundant cloud water, especially the accumulation region of high supercooled water (cloud water) near the 0 °C layer, is the key to the formation of hail embryos, in which qc is up to 1.92 g·kg−1 at the −4~−2 °C layer. The hail embryos mainly grow by collision-coalescence (collision-freezing) with cloud water (supercooled cloud drops) and snow crystal riming.
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CHERNOKULSKY, A. V., A. V. ELISEEV, F. A. KOZLOV, N. N. KORSHUNOVA, M. V. KURGANSKY, I. I. MOKHOV, V. A. SEMENOV, N. V. SHVETS', A. N. SHIKHOV i YU I. YARINICH. "ATMOSPHERIC SEVERE CONVECTIVE EVENTS IN RUSSIA: CHANGES OBSERVED FROM DIFFERENT DATA". Meteorologiya i Gidrologiya, nr 5 (maj 2022): 27–41. http://dx.doi.org/10.52002/0130-2906-2022-5-27-41.
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Changes in the frequency and intensity of atmospheric severe convective events, including heavy rainfall, thunderstorm, hailstorm, squall, and tornado, in the Russian regions during the warm season are analyzed using different independent sources of information. Based on observations at Russian weather stations in 1966-2020, the frequency of thunderstorm, hailstorm, and strong wind, the contribution of extreme showers to total precipitation, and the cumulonimbus cloud fraction are estimated. Based on satellite data, the frequency and intensity of tornado and squall events that caused windthrows for 1986-2021 and the height of the top of deep convective clouds for 2002-2021 are also evaluated. The ERA5 reanalysis data are used to analyze the frequency of conditions favorable for the development of moderate and intense severe convective events in 1979-2020. The results indicate a general intensification of severe convective events in most Russian regions, except for a number of regions in the south of the European part of Russia. The frequency of moderate hazards has a decreasing trend, and the frequency of the most intense severe hazards has an increasing trend. It is reasonable to take the results into account when developing plans for the adaptation of Russian regions and industries to climate change.
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Chaboureau, Jean-Pierre, Laurent Labbouz, Cyrille Flamant i Alma Hodzic. "Acceleration of the southern African easterly jet driven by the radiative effect of biomass burning aerosols and its impact on transport during AEROCLO-sA". Atmospheric Chemistry and Physics 22, nr 13 (5.07.2022): 8639–58. http://dx.doi.org/10.5194/acp-22-8639-2022.
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Abstract. The direct and semi-direct radiative effects of biomass burning aerosols (BBAs) are investigated over southern Africa and the southeastern Atlantic during the Aerosols, Radiation and Clouds in southern Africa (AEROCLO-sA) field campaign in September 2017. A reference convection-permitting simulation has been performed using the Meso-NH model with an online dust emission scheme, a strongly absorbing BBA tracer emitted using the daily Global Fire Emissions Database and online-computed backward Lagrangian trajectories. The simulation captures both the aerosol optical depth and the vertical distribution of aerosols as observed from airborne and spaceborne lidars. The occurrence of stratocumulus over the southeastern Atlantic, deep convective clouds over equatorial Africa and the large-scale circulation are all reproduced by the model. If the radiative effects of BBA are omitted in the model, we show that (i) the smoke plume is too low in altitude, (ii) the low-cloud cover is too weak, (iii) the deep convective activity is too frequent but not intense enough, (iv) the Benguela low-level jet is too strong, and (v) the southern African easterly jet is too weak. The Lagrangian analysis indicates that the radiative effect of BBA leads to the transport of BBA to higher altitudes, farther southwest and with a stronger diurnal oscillation. The higher smoke plume altitude can be explained by a combination of three factors: increased upward motion induced by the stronger southern African easterly jet, self-lofting of BBA and reduced subsidence associated with less frequent deep convective activity over western equatorial Africa.
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Lee, Jae-Deok, Chun-Chieh Wu i Kosuke Ito. "Diurnal Variation of the Convective Area and Eye Size Associated with the Rapid Intensification of Tropical Cyclones". Monthly Weather Review 148, nr 10 (1.10.2020): 4061–82. http://dx.doi.org/10.1175/mwr-d-19-0345.1.
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AbstractThis study examines the diurnal variation of the convective area and eye size of 30 rapidly intensifying tropical cyclones (RI TCs) that occurred in the western North Pacific from 2015 to 2017 utilizing Himawari-8 satellite imagery. The convective area can be divided into the active convective area (ACA), mixed phase, and inactive convective area (IACA) based on specific thresholds of brightness temperature. In general, ACA tends to develop vigorously from late afternoon to early the next morning, while mixed phase and IACA develop during the day. This diurnal pattern indicates the potential for ACA to evolve into mixed phase or IACA over time. From the 30 samples, RI TCs tend to have at least a single-completed diurnal signal of ACA inside the radius of maximum wind (RMW) during the rapidly intensifying period. In the same period, the RMW also contracts significantly. Meanwhile, more intense storms such as those of category 4 or 5 hurricane intensity are apt to have continuous ACA inside the RMW and maintain eyewall convective clouds. These diurnal patterns of the ACA could vary depending on the impact of large-scale environments such as vertical wind shear, ocean heat content, environmental mesoscale convection, and terrain. The linear regression analysis shows that from the tropical storm stage, RI commences after a slow intensification period, which enhances both the primary circulation and eyewall convective cloud. Finally, after the eye structure appears in satellite imagery, its size changes inversely to the diurnal variation of the convective activity (e.g., the eye size becomes larger during the daytime).
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Mace, Gerald G., Min Deng, Brian Soden i Ed Zipser. "Association of Tropical Cirrus in the 10–15-km Layer with Deep Convective Sources: An Observational Study Combining Millimeter Radar Data and Satellite-Derived Trajectories". Journal of the Atmospheric Sciences 63, nr 2 (1.02.2006): 480–503. http://dx.doi.org/10.1175/jas3627.1.
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Abstract In this paper, millimeter cloud radar (MMCR) and Geosynchronous Meteorological Satellite (GMS) data are combined to study the properties of tropical cirrus that are common in the 10–15-km layer of the tropical troposphere in the western Pacific. Millimeter cloud radar observations collected by the Atmospheric Radiation Measurement program on the islands of Manus and Nauru in the western and central equatorial Pacific during a 12-month period spanning 1999 and 2000 show differences in cirrus properties: over Manus, where clouds above 7 km are observed 48% of the time, the cirrus are thicker and warmer on average and the radar reflectivity and Doppler velocity are larger; over Nauru clouds above 7 km are observed 23% of time. To explain the differences in cloud properties, the relationship between tropical cirrus and deep convection is examined by combining the radar observations with GMS satellite-derived back trajectories. Using a data record of 1 yr, it is found that 47% of the cirrus observed over Manus can be traced to a deep convective source within the past 12 h while just 16% of the cirrus observed over Nauru appear to have a convective source within the previous 12 h. Of the cirrus that can be traced to deep convection, the evolution of the radar-observed cloud properties is examined as a function of apparent cloud age. The radar Doppler moments and ice water path of the observed cirrus at both sites generally decrease as the cirrus age increase. At Manus, it is found that cirrus during boreal winter typically advect over the site from the southeast from convection associated with the winter monsoon, while during boreal summer, the trajectories are mainly from the northeast. The properties of these two populations of cirrus are found to be different, with the winter cirrus having higher concentrations of smaller particles. Examining statistics of the regional convection using Tropical Rainfall Measuring Mission (TRMM), it is found that the properties of the winter monsoon convection in the cirrus source region are consistent with more intense convection compared to the convection in the summer source region.
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Lane, Todd P., i Robert D. Sharman. "Some Influences of Background Flow Conditions on the Generation of Turbulence due to Gravity Wave Breaking above Deep Convection". Journal of Applied Meteorology and Climatology 47, nr 11 (1.11.2008): 2777–96. http://dx.doi.org/10.1175/2008jamc1787.1.
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Abstract Deep moist convection generates turbulence in the clear air above and around developing clouds, penetrating convective updrafts and mature thunderstorms. This turbulence can be due to shearing instabilities caused by strong flow deformations near the cloud top, and also to breaking gravity waves generated by cloud–environment interactions. Turbulence above and around deep convection is an important safety issue for aviation, and improved understanding of the conditions that lead to out-of-cloud turbulence formation may result in better turbulence avoidance guidelines or forecasting capabilities. In this study, a series of high-resolution two- and three-dimensional model simulations of a severe thunderstorm are conducted to examine the sensitivity of above-cloud turbulence to a variety of background flow conditions—in particular, the above-cloud wind shear and static stability. Shortly after the initial convective overshoot, the above-cloud turbulence and mixing are caused by local instabilities in the vicinity of the cloud interfacial boundary. At later times, when the convection is more mature, gravity wave breaking farther aloft dominates the turbulence generation. This wave breaking is caused by critical-level interactions, where the height of the critical level is controlled by the above-cloud wind shear. The strength of the above-cloud wind shear has a strong influence on the occurrence and intensity of above-cloud turbulence, with intermediate shears generating more extensive regions of turbulence, and strong shear conditions producing the most intense turbulence. Also, more stable above-cloud environments are less prone to turbulence than less stable situations. Among other things, these results highlight deficiencies in current turbulence avoidance guidelines in use by the aviation industry.
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Tompkins, Adrian M., i Adeyemi A. Adebiyi. "Using CloudSat Cloud Retrievals to Differentiate Satellite-Derived Rainfall Products over West Africa". Journal of Hydrometeorology 13, nr 6 (1.12.2012): 1810–16. http://dx.doi.org/10.1175/jhm-d-12-039.1.
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Abstract Daily precipitation retrievals from three algorithms [the Tropical Rainfall Measuring Mission 3B42 rain product (TRMM-3B42), the Climate Prediction Center morphing technique (CMORPH), and the second version (RFEv2) of the Famine Early Warning System (FEWS)] and CloudSat retrievals of cloud liquid water, ice amount, and cloud fraction are used to document the cloud structures associated with rainfall location and intensity in the West African monsoon. The different rainfall retrieval approaches lead to contrasting cloud sensitivities between all three algorithms most apparent in the onset period of June and July. During the monsoon preonset phase, CMORPH produces a precipitation peak at around 12°N associated with upper-level cirrus clouds, while FEWS and TRMM both produce rainfall maxima collocated with the tropospheric–deep convective cloud structures at 4°–6°N. In July similar relative displacements of the rainfall maxima are observed. Conditional sampling of several hundred convection systems proves that, while upper-level cirrus is advected northward relative to the motion of the convective system cores, the reduced cover and water content of lower-tropospheric clouds in the northern zone could be due to signal attenuation as the systems there appear to be more intense, producing higher ice water contents. Thus, while CMORPH may overestimate rainfall in the northern zone due to its reliance on cloud ice, TRMM and FEWS are likely underestimating precipitation in this zone, potentially due to the use of infrared based products in TRMM and FEWS when microwave is not available. Mapping the CloudSat retrievals as a function of rain rate confirms the greater sensitivity of CMORPH to ice cloud and indicates that high-intensity rainfall events are associated with systems that are deeper and of a greater spatial scale.
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Grell, G., S. R. Freitas, M. Stuefer i J. Fast. "Inclusion of biomass burning in WRF-Chem: impact of wildfires on weather forecasts". Atmospheric Chemistry and Physics 11, nr 11 (6.06.2011): 5289–303. http://dx.doi.org/10.5194/acp-11-5289-2011.
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Abstract. A plume rise algorithm for wildfires was included in WRF-Chem, and applied to look at the impact of intense wildfires during the 2004 Alaska wildfire season on weather simulations using model resolutions of 10 km and 2 km. Biomass burning emissions were estimated using a biomass burning emissions model. In addition, a 1-D, time-dependent cloud model was used online in WRF-Chem to estimate injection heights as well as the vertical distribution of the emission rates. It was shown that with the inclusion of the intense wildfires of the 2004 fire season in the model simulations, the interaction of the aerosols with the atmospheric radiation led to significant modifications of vertical profiles of temperature and moisture in cloud-free areas. On the other hand, when clouds were present, the high concentrations of fine aerosol (PM2.5) and the resulting large numbers of Cloud Condensation Nuclei (CCN) had a strong impact on clouds and cloud microphysics, with decreased precipitation coverage and precipitation amounts during the first 12 h of the integration. During the afternoon, storms were of convective nature and appeared significantly stronger, probably as a result of both the interaction of aerosols with radiation (through an increase in CAPE) as well as the interaction with cloud microphysics.
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Siqueira, José Ricardo, i Valdo da Silva Marques. "Tracking and short-term forecasting of mesoscale convective cloud clusters over southeast Brazil using satellite infrared imagery". Journal of Southern Hemisphere Earth Systems Science 71, nr 1 (2021): 1. http://dx.doi.org/10.1071/es19050.
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This paper presents the tracking and short-term forecasting of mesoscale convective cloud clusters (CCs) that occurred over southeast Brazil and the adjacent Atlantic Ocean during 2009–17. These events produce intense rainfall and severe storms that impact agriculture, defence, hydroelectricity and offshore oil production. To identify, track and forecast CCs, the Geostationary Operational Environmental Satellite infrared imagery and the Forecasting and Tracking the Evolution of Cloud Clusters method are used. The forecast performance is investigated by applying statistical analyses between the observed and forecasted CCs’ physical properties. A total of 7139 mesoscale convective CCs were identified, tracked and selected for the short-term forecasting at their maturation phases. The CC tracking showed a high frequency of CCs over the Atlantic Ocean and mainly over continental and coastal southeast Brazil during the wet season. This indicates an important role played by the cold fronts and convective diurnal forcing on the organisation of convective cloudiness over that region. The majority of the CCs reached their maturation phases within the first 2h of life cycle, which occurred mostly between the late afternoon and evening. The CCs had short lifetimes and were predominantly in meso-β scales, followed by meso-α convective CCs. The CCs showed cloud-top temperatures typical of clouds with strong vertical development and potential to produce rainfall. The short-term forecasting of CCs at their maturation phases revealed different behaviours of the statistical indices with forecast range. For the 30–60-min timeframe, the forecasts performed relatively well. For longer forecast lead times (90–120min), the forecasts overestimated the occurrences, intensities and growth of the CCs and forecasted the CCs to be further north and east of their actual observed locations. Overall, our results may contribute to improving the forecast quality of these intense weather events.
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Battaglia, Alessandro, Simone Tanelli i Pavlos Kollias. "Polarization Diversity for Millimeter Spaceborne Doppler Radars: An Answer for Observing Deep Convection?" Journal of Atmospheric and Oceanic Technology 30, nr 12 (1.12.2013): 2768–87. http://dx.doi.org/10.1175/jtech-d-13-00085.1.
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Abstract Spaceborne Doppler radars have the potential to provide key missing observations of convective vertical air motions especially over the tropical oceans. Such measurements can improve understanding of the role of tropical convection in vertical energy transport and its interaction with the environment. Several millimeter wavelength Doppler radar concepts have been proposed since the 1990s. The Earth Clouds, Aerosols, and Radiation Explorer (EarthCARE) Cloud Profiling Radar (CPR) will be the first Dopplerized atmospheric radar in space but has not been optimized for Doppler measurements in deep convective clouds. The key challenge that constrains the CPR performance in convective clouds is the range–Doppler dilemma. Polarization diversity (PD) offers a solution to this constraint by decoupling the coherency (Doppler) requirement from the unambiguous range requirement. Careful modeling of the radar signal depolarization and its impact on radar receiver channel cross talk is needed to accurately assess the performance of the PD approach. The end-to-end simulator presented in this work allows reproduction of the signal sensed by a Doppler radar equipped with polarization diversity when overpassing realistic three-dimensional convective cells, with all relevant cross-talk sources accounted for. The notional study highlights that multiple scattering is the primary source of cross talk, highly detrimental for millimeter Doppler velocity accuracy. The ambitious scientific requirement of 1 m s−1 accuracy at 500-m integration for reflectivities above −15 dBZ are within reach for a W-band radar with a 2.5-m antenna with optimal values of the pulse-pair interval between 20 and 30 μs but only once multiple scattering and ghost-contaminated regions are screened out. The identification of such areas is key for Doppler accuracies and can be achieved by employing an interlaced pulse-pair mode that measures the cross and the copolar reflectivities. To mitigate the impact of attenuation and multiple scattering, the Ka band has been considered as either alternative or additional to the W band. However, a Ka system produces worse Doppler performances than a W-band system with the same 2.5-m antenna size. Furthermore, in deep convection it results in similar levels of multiple scattering and therefore it does not increase significantly the depth of penetration. In addition, the larger footprint causes stronger nonuniform beam-filling effects. One advantage of the Ka-band option is the larger Nyquist velocity that tends to reduce the Doppler accuracies. More significant benefits are derived from the Ka band when observing precipitation not as intense as the deep convection is considered here. This study demonstrates that polarization diversity indeed represents a very promising methodology capable of significantly reducing aliasing and Doppler moment estimate errors, two main error sources for Doppler velocity estimates in deep convective systems and a key step to achieving typical mission requirements for convection-oriented millimeter radar-based spaceborne missions.
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Seifert, Axel, Alexander Khain, Ulrich Blahak i Klaus D. Beheng. "Possible Effects of Collisional Breakup on Mixed-Phase Deep Convection Simulated by a Spectral (Bin) Cloud Model". Journal of the Atmospheric Sciences 62, nr 6 (1.06.2005): 1917–31. http://dx.doi.org/10.1175/jas3432.1.
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Abstract The effects of the collisional breakup of raindrops are investigated using the Hebrew University Cloud Model (HUCM). The parameterizations, which are combined in the new breakup scheme, are those of Low and List, Beard and Ochs, as well as Brown. A sensitivity study reveals strong effects of collisional breakup on the precipitation formation in mixed-phase deep convective clouds for strong as well as for weak precipitation events. Collisional breakup reduces the number of large raindrops, increases the number of small raindrops, and, as a consequence, decreases surface rain rates and considerably reduces the speed of rain formation. In addition, it was found that including breakup can lead to a more intense triggering of secondary convective cells. But a statistical comparison with observed raindrop size distributions shows that the parameterizations might systematically overestimate collisional breakup.
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Hu, Jiaxi, Daniel Rosenfeld, Alexander Ryzhkov i Pengfei Zhang. "Synergetic Use of the WSR-88D Radars, GOES-R Satellites, and Lightning Networks to Study Microphysical Characteristics of Hurricanes". Journal of Applied Meteorology and Climatology 59, nr 6 (czerwiec 2020): 1051–68. http://dx.doi.org/10.1175/jamc-d-19-0122.1.
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AbstractThis study analyzes the microphysics and precipitation pattern of Hurricanes Harvey (2017) and Florence (2018) in both the eyewall and outer rainband regions. From the retrievals by a satellite red–green–blue scheme, the outer rainbands show a strong convective structure while the inner eyewall has less convective vigor (i.e., weaker upper-level reflectivities and electrification), which may be related to stronger vertical wind shear that hinders fast vertical motions. The WSR-88D column-vertical profiles further confirm that the outer rainband clouds have strong vertical motion and large ice-phase hydrometeor formation aloft, which correlates well with 3D Lightning Mapping Array source counts in height and time. From the results from this study, it is determined that the inner eyewall region is dominated by warm rain, whereas the external rainband region contains intense mixed-phase precipitation. External rainbands are defined here as those that reside outside of the main hurricane circulation, associated with surface tropical storm wind speeds. The synergy of satellite and radar dual-polarization parameters is instrumental in distinguishing between the key microphysical features of intense convective rainbands and the warm-rain-dominated eyewall regions within the hurricanes. Substantial amounts of ice aloft and intense updrafts in the external rainbands are indicative of heavy surface precipitation, which can have important implications for severe weather warnings and quantitative precipitation forecasts. The novel part of this study is to combine ground-based radar measurement with satellite observations to study hurricane microphysical structure from surface to cloud top so as to fill in the gaps between the two observational techniques.
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Argüeso, D., R. Romero i V. Homar. "Precipitation Features of the Maritime Continent in Parameterized and Explicit Convection Models". Journal of Climate 33, nr 6 (15.03.2020): 2449–66. http://dx.doi.org/10.1175/jcli-d-19-0416.1.
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AbstractThe Maritime Continent is the largest archipelago in the world and a region of intense convective activity that influences Earth’s general circulation. The region features one of the warmest oceans, very complex topography, dense vegetation, and an intricate configuration of islands, which together result in very specific precipitation characteristics, such as a marked diurnal cycle. Atmospheric models poorly resolve deep convection processes that generate rainfall in the archipelago and show fundamental errors in simulating precipitation. Spatial resolution and the use of convective schemes required to represent subgrid convective circulations have been pointed out as culprits of these errors. However, models running at the kilometer scale explicitly resolve most convective systems and thus are expected to contribute to solve the challenge of accurately simulating rainfall in the Maritime Continent. Here we investigate the differences in simulated precipitation characteristics for different representations of convection, including parameterized and explicit, and at various spatial resolutions. We also explore the vertical structure of the atmosphere in search of physical mechanisms that explain the main differences identified in the rainfall fields across model experiments. Our results indicate that both increased resolution and representing convection explicitly are required to produce a more realistic simulation of precipitation features, such as a correct diurnal cycle both over land and ocean. We found that the structures of deep and shallow clouds are the main differences across experiments and thus they are responsible for differences in the timing and spatial distribution of rainfall patterns in the various convection representation experiments.
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Wu, Ruoting, i Guixing Chen. "Contrasting Cloud Regimes and Associated Rainfall over the South Asian and East Asian Monsoon Regions". Journal of Climate 34, nr 9 (maj 2021): 3663–81. http://dx.doi.org/10.1175/jcli-d-20-0992.1.
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AbstractThe Asian monsoon has large spatial and temporal variabilities in winds and precipitation. This study reveals that the Asian monsoon also exhibits pronounced regional differences in cloud regimes and cloud–rainfall relationship at a wide range of time scales from diurnal to seasonal to interannual. Over South (East) Asia, the convectively active regime of deep convection (CD) occurs frequently in June–September (March–September) with a late-afternoon peak (morning feature). The intermediate mixture (IM) regime over South Asia mainly occurs in summer and maximizes near noon. It develops as CD at late afternoon and dissipates as convective cirrus (CC) after midnight, showing a life cycle of thermal convection in response to solar radiation. Over East Asia, IM is dominant in cold seasons with a small diurnal cycle, indicating a prevalence of midlevel stratiform clouds. Further analyses show that CD and CC contribute 80%–90% of the rainfall amount and most of the intense rainfall in the two key regions. The CD-related rainfall also accounts for the pronounced diurnal cycles of summer rainfall with a late-afternoon peak (morning feature) over northern India (Southeast China). The afternoon CD-related rainfall mainly results from thermal convection under the moderate humidity but warm conditions particularly over northern India, while the morning CD-related rainfall over Southeast China is more related to the processes with high humidity. The CD/CC-related rainfall also exhibits large interannual variations that explain ~90% of the interannual variance of summer rainfall. The interannual variations of CD/CC occurrence are positively correlated with the moist southerlies and induced convergence, especially over Southeast China, suggesting a close relationship between cloud regimes and monsoon activities.
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Gayet, J. F., G. Mioche, L. Bugliaro, A. Protat, A. Minikin, M. Wirth, A. Dörnbrack i in. "On the observation of unusual high concentration of small chain-like aggregate ice crystals and large ice water contents near the top of a deep convective cloud during the CIRCLE-2 experiment". Atmospheric Chemistry and Physics Discussions 11, nr 8 (25.08.2011): 23911–58. http://dx.doi.org/10.5194/acpd-11-23911-2011.
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Abstract. During the CIRCLE-2 experiment carried out over Western Europe in May 2007, combined in situ and remote sensing observations allowed to describe microphysical and optical properties near-top of an overshooting convective cloud (11 080 m/−58 °C). The airborne measurements were performed with the DLR Falcon aircraft specially equipped with a unique set of instruments for the extensive in situ cloud measurements of microphysical and optical properties (Polar Nephelometer, FSSP-300, Cloud Particle Imager and PMS 2D-C) and nadir looking remote sensing observations (DLR WALES Lidar). Quasi-simultaneous space observations from MSG/SEVIRI, CALIPSO/CALIOP-WFC-IIR and CloudSat/CPR combined with airborne RASTA radar reflectivity from the French Falcon aircraft flying above the DLR Falcon depict very well convective cells which overshoot by up to 600 m the tropopause level. Unusual high values of the concentration of small ice particles, extinction, ice water content (up to 70 cm−3, 30 km−1 and 0.5 g m−3, respectively) are experienced. This very dense cloud causes a strong attenuation of the WALES and CALIOP lidar returns. The mean effective diameter is of 43 μm and the maximum particle size is about 300 μm. The SEVIRI retrieved parameters confirm the occurrence of small ice crystals at the top of the convective cell. Smooth and featureless phase functions with asymmetry factors of 0.776 indicate fairly uniform optical properties. Due to small ice crystals the power-law relationship between ice water content (IWC) and radar reflectivity appears to be very different from those usually found in cirrus and anvil clouds. For a given equivalent reflectivity factor, IWCs are significantly larger for the overshooting cell than for the cirrus. Assuming the same prevalent microphysical properties over the depth of the overshooting cell, RASTA reflectivity profiles scaled into ice water content show that retrieved IWC up to 1 g m−3 may be observed near the cloud top. Extrapolating the relationship for stronger convective clouds with similar ice particles, IWC up to 5 g m−3 could be experienced with reflectivity factors no larger than about 20 dBZ. This means that for similar situations, indication of rather weak radar echo does not necessarily warn the occurrence of high ice water content carried by small ice crystals. All along the cloud penetration the shape of the ice crystals is dominated by chain-like aggregates of frozen droplets. Our results confirm previous observations that the chains of ice crystals are found in a continental deep convective systems which are known generally to generate intense electric fields causing efficient ice particle aggregation processes. Vigorous updrafts could lift supercooled droplets which are frozen extremely rapidly by homogeneous nucleation near the −37 °C level, producing therefore high concentrations of very small ice particles at upper altitudes. They are sufficient to deplete the water vapour and suppress further nucleation as confirmed by humidity measurements. These observations address scientific issues related to the microphysical properties and structure of deep convective clouds and confirm that particles smaller than 50 μm may control the radiative properties in convective-related clouds. These unusual observations may also provide some possible insights regarding engineering issues related to the failure of jet engines commonly used on commercial aircraft during flights through areas of high ice water content.
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Gayet, J. F., G. Mioche, L. Bugliaro, A. Protat, A. Minikin, M. Wirth, A. Dörnbrack i in. "On the observation of unusual high concentration of small chain-like aggregate ice crystals and large ice water contents near the top of a deep convective cloud during the CIRCLE-2 experiment". Atmospheric Chemistry and Physics 12, nr 2 (16.01.2012): 727–44. http://dx.doi.org/10.5194/acp-12-727-2012.
Pełny tekst źródłaStreszczenie:
Abstract. During the CIRCLE-2 experiment carried out over Western Europe in May 2007, combined in situ and remote sensing observations allowed to describe microphysical and optical properties near-top of an overshooting convective cloud (11 080 m/−58 °C). The airborne measurements were performed with the DLR Falcon aircraft specially equipped with a unique set of instruments for the extensive in situ cloud measurements of microphysical and optical properties (Polar Nephelometer, FSSP-300, Cloud Particle Imager and PMS 2-D-C) and nadir looking remote sensing observations (DLR WALES Lidar). Quasi-simultaneous space observations from MSG/SEVIRI, CALIPSO/CALIOP-WFC-IIR and CloudSat/CPR combined with airborne RASTA radar reflectivity from the French Falcon aircraft flying above the DLR Falcon depict very well convective cells which overshoot by up to 600 m the tropopause level. Unusual high values of the concentration of small ice particles, extinction, ice water content (up to 70 cm−3, 30 km−1 and 0.5 g m−3, respectively) are experienced. The mean effective diameter and the maximum particle size are 43 μm and about 300 μm, respectively. This very dense cloud causes a strong attenuation of the WALES and CALIOP lidar returns. The SEVIRI retrieved parameters confirm the occurrence of small ice crystals at the top of the convective cell. Smooth and featureless phase functions with asymmetry factors of 0.776 indicate fairly uniform optical properties. Due to small ice crystals the power-law relationship between ice water content (IWC) and radar reflectivity appears to be very different from those usually found in cirrus and anvil clouds. For a given equivalent reflectivity factor, IWCs are significantly larger for the overshooting cell than for the cirrus. Assuming the same prevalent microphysical properties over the depth of the overshooting cell, RASTA reflectivity profiles scaled into ice water content show that retrieved IWC up to 1 g m−3 may be observed near the cloud top. Extrapolating the relationship for stronger convective clouds with similar ice particles, IWC up to 5 g m−3 could be experienced with reflectivity factors no larger than about 20 dBZ. This means that for similar situations, indication of rather weak radar echo does not necessarily warn the occurrence of high ice water content carried by small ice crystals. All along the cloud penetration the shape of the ice crystals is dominated by chain-like aggregates of frozen droplets. Our results confirm previous observations that the chains of ice crystals are found in a continental deep convective systems which are known generally to generate intense electric fields causing efficient ice particle aggregation processes. Vigorous updrafts could lift supercooled droplets which are frozen extremely rapidly by homogeneous nucleation near the −37 °C level, producing therefore high concentrations of very small ice particles at upper altitudes. They are sufficient to deplete the water vapour and suppress further nucleation as confirmed by humidity measurements. These observations address scientific issues related to the microphysical properties and structure of deep convective clouds and confirm that particles smaller than 50 μm may control the radiative properties in convective-related clouds. These unusual observations may also provide some possible insights regarding engineering issues related to the failure of jet engines commonly used on commercial aircraft during flights through areas of high ice water content. However, large uncertainties of the measured and derived parameters limit our observations.
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Andari, Bayu Retna Tri, Nurjanna Joko Trilaksono i Muhammad Arif Munandar. "Turbulence analysis on the flight of Etihad airways in Bangka Island using the WRF case study May 4, 2016". Jurnal Meteorologi dan Geofisika 23, nr 3 (8.08.2022): 65. http://dx.doi.org/10.31172/jmg.v23i3.912.
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<p>Accurate weather forecasts should support the increase in safety of aviation operations in Indonesia. This weather forecast is needed, especially in detecting turbulence, considering that geographically Indonesia has effective solar radiation resulting in convective cloud formation. Convective clouds can trigger turbulence then produce disruption and even accidents on flights. This research uses a case study on the Etihad Airways flight on Bangka Island on May 4, 2016. At the time of the incident, there was turbulence at 39,000 feet altitude, and the aircraft did not enter the cloudy area. The Weather Research and Forecasting (WRF) model is used to simulate the turbulence in this study, which is downscaled up to 3 km with a microphysics parameterization of WRF Single Moment 6 Class (WSM6). The results were then verified using correlation and linear regression for temperature, wind direction, wind speed, and pattern resemblance between cloud fraction and the convective nuclei distribution. The turbulence is analyzed from the south-north and west-east vertical airflow. The turbulence spotted at 06.40 UTC when there is a quite strong updraft which can cause turbulence. The turbulence parameters used, such as the eddy dissipation rate (EDR) parameter, which has a value of 0.05 , Richardson number with a value of less than 0.25, and turbulence index (TI 1) with a maximum value of 4 x 10<sup>-7</sup> s<sup>-2</sup> found that turbulence was in a strong category. The turbulence that occurs in this study is identified as near cloud turbulence (NCT) event due to cloud formation observed in the west of the turbulence and intense updraft activity at the location of turbulence.</p>
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Siburian, R., I. J. A. Saragih, M. Situmorang, K. Tarigan, K. Sembiring, M. Sinambela i S. Humaidi. "Simulation of atmospheric dynamics during heavy rain events on Nias Island using WRF model and Himawari-8 satellite data". Journal of Physics: Conference Series 2019, nr 1 (1.10.2021): 012099. http://dx.doi.org/10.1088/1742-6596/2019/1/012099.
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Abstract Nias is the largest island in the Indian Ocean west of Sumatra. The geographical condition of Nias Island which is a small island surrounded by waters causes strong weather dynamics and high intensity of rainfall. This study was conducted to determine changes in weather dynamics conditions during high rainfall on Nias Island, including the parameters of the vertical profile of air humidity, vorticity, divergence, vertical velocity, reflectivity; and cloud top temperatures. The simulation was carried out on 4 days of heavy rain in 2020, each representing each season period, namely 7 February 2020 for December-January-February (DJF), 30 April 2020 for March-April-May (MAM), 3 August 2020 for June-July-August (JJA), and 8 October 2020 for September-October-November (SON). The data used are Final Analysis Data (FNL) with a spatial resolution of 1°x1° as input data for the Weather Research and Forecast (WRF) model, IR1 data (band#13 – 10.4µm) Himawari-8 satellite, and observational rainfall data from the Binaka and Global Meteorological Stations. Precipitation Measurement – The Integrated Multi-Satellite Retrievals for GPM (GPM IMERG) with a spatial resolution of 0.1°x0.1°. The results showed that the presence of Cumulonimbus convective clouds caused heavy rain, with cloud top temperatures reaching -60°C to -80°C. The relatively humid atmosphere, accompanied by the convection mechanism that occurs, causes the convective activity on Nias Island to be quite intense.
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Zuidema, Paquita, Brian Mapes, Jialin Lin, Chris Fairall i Gary Wick. "The Interaction of Clouds and Dry Air in the Eastern Tropical Pacific". Journal of Climate 19, nr 18 (15.09.2006): 4531–44. http://dx.doi.org/10.1175/jcli3836.1.
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Abstract Cloud radar observations of eastern Pacific intertropical convergence zone cloud vertical structure are interpreted in light of soundings, 100-km-scale divergence profiles calculated from precipitation radar Doppler velocities, and surface rain gauge data, from a ship at 10°N, 95°W during the 2001 East Pacific Investigation of Climate (EPIC) experiment. The transition from convective to stratiform rain is clear in all four datasets, indicating a coherence from local to 100-km scale. A novel finding is dry air intrusions at altitudes of 6–8 km, often undercutting upper-level ice clouds. Two distinct dry air source regions are identified. One is a relatively dry area overlying the cooler waters of the Costa Rica oceanic thermocline dome, centered approximately 400 km east-northeast of the ship site. The other is the even drier near-equatorial subsidence zone south of 6°–7°N. The former source is somewhat peculiar to this specific ship location, so that the ship sample is not entirely representative of the region. The 20–25 September period is studied in detail, as it depicts two influences of the dry air on cloud vertical structure. One is the modulation of small-scale surface-based convection, evident as a weakening and narrowing of cloud radar reflectivity features. The other springs from intense sublimation cooling as differential advection brought snowing anvil clouds over the dry layers. During one half-day period of strong sublimation, the cooling rate is inferred to be several tens of degrees per day over a 100-hPa layer, based on a heat budget estimate at 100-km scale involving the horizontal wind divergence data. This is consistent with fluxing ice water contents of 0.05–0.10 g m−3 derived from the cloud radar reflectivities. The temperature profile shows the dynamically expected response to this cooling, a positive–negative–positive temperature anomaly pattern centered on the sublimating layer. A buoyancy-sorting diagnostic model of convection indicates that these upper-troposphere temperature anomalies can cause premature detrainment of updrafts into the lower part of the cloudy layer, a feedback that may actively maintain these long-lasting dense anvils. Middle-troposphere southerly dry air inflow is also evident in large-scale analysis. Given the proximity of the dry equatorial subsidence zone to the eastern tropical Pacific, the differential advection of dry and cloudy air, the ensuing sublimation, and its dynamical aftereffects may play a role in establishing the region’s climate, although the extent of their significance needs to be further established.
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Machado, Luiz A. T., Maria A. F. Silva Dias, Carlos Morales, Gilberto Fisch, Daniel Vila, Rachel Albrecht, Steven J. Goodman i in. "The Chuva Project: How Does Convection Vary across Brazil?" Bulletin of the American Meteorological Society 95, nr 9 (1.09.2014): 1365–80. http://dx.doi.org/10.1175/bams-d-13-00084.1.
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CHUVA, meaning “rain” in Portuguese, is the acronym for the Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud-Resolving Modeling and to the Global Precipitation Measurement (GPM). The CHUVA project has conducted five field campaigns; the sixth and last campaign will be held in Manaus in 2014. The primary scientific objective of CHUVA is to contribute to the understanding of cloud processes, which represent one of the least understood components of the weather and climate system. The five CHUVA campaigns were designed to investigate specific tropical weather regimes. The first two experiments, in Alcantara and Fortaleza in northeastern Brazil, focused on warm clouds. The third campaign, which was conducted in Belém, was dedicated to tropical squall lines that often form along the sea-breeze front. The fourth campaign was in the Vale do Paraiba of southeastern Brazil, which is a region with intense lightning activity. In addition to contributing to the understanding of cloud process evolution from storms to thunderstorms, this fourth campaign also provided a high-fidelity total lightning proxy dataset for the NOAA Geostationary Operational Environmental Satellite (GOES)-R program. The fifth campaign was carried out in Santa Maria, in southern Brazil, a region of intense hailstorms associated with frequent mesoscale convective complexes. This campaign employed a multimodel high-resolution ensemble experiment. The data collected from contrasting precipitation regimes in tropical continental regions allow the various cloud processes in diverse environments to be compared. Some examples of these previous experiments are presented to illustrate the variability of convection across the tropics.