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Kumar, Shailendra. "Vertical Characteristics of Reflectivity in Intense Convective Clouds using TRMM PR Data." Environment and Natural Resources Research 7, no. 2 (May 15, 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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Kumar, Shailendra, and G. S. Bhat. "Vertical Profiles of Radar Reflectivity Factor in Intense Convective Clouds in the Tropics." Journal of Applied Meteorology and Climatology 55, no. 5 (May 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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Biondi, R., W. J. Randel, S. P. Ho, T. Neubert, and S. Syndergaard. "Thermal structure of intense convective clouds derived from GPS radio occultations." Atmospheric Chemistry and Physics Discussions 11, no. 10 (October 27, 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, and S. Syndergaard. "Thermal structure of intense convective clouds derived from GPS radio occultations." Atmospheric Chemistry and Physics 12, no. 12 (June 18, 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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Yeh, H.-Y. M., N. Prasad, R. Meneghini, W.-K. Tao, J. A. Jones, and R. F. Adler. "Cloud Model-Based Simulation of Spaceborne Radar Observations." Journal of Applied Meteorology 34, no. 1 (January 1, 1995): 175–97. http://dx.doi.org/10.1175/1520-0450-34.1.175.
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Abstract Simulations of observations from potential spaceborne radars are made based on storm structure generated from the three-dimensional (3D) Goddard cumulus ensemble model simulation of an intense overland convective system. Five frequencies of 3, 10, 14, 35, and 95 GHz are discussed, but the Tropical Rainfall Measuring Mission precipitation radar sensor frequency ( 14 GHz) is the focus of this study. Radar reflectivities and their attenuation in various atmospheric conditions are studied in this simulation. With the attenuation from cloud and precipitation in the estimation of reflectivity factor (dBZ), the reflectivities in the lower atmosphere in the convective coresare significantly reduced. With spatial resolution of 4 km X 4 km, attenuation at 14 GHz may cause as large as a 20-dBZ difference between the simulated measurements of the peak (Zmp) and near-surface reflectivity (Zmp) in the most intense convective region. The Zmp occurs at various altitudes depending on the hydrometeor concentrations and their vertical distribution. Despite the significant attenuation in the intense cores, the presence of the rain maximum is easily detected by using information of Zmp. In the stratiform region, the attenuation is quite limited (usually less than 5 dBZ), and the reduction of reflectivity is mostly related to the actual vertical structure of cloud distribution. Since Zmp suffers severe attenuation and tends to underestimate surface rainfall intensity in convective regions, Zmp can be more representative for rainfall retrieval in the lower atmosphere in these regions. In the stratiform region where attenuation is negligible, however, Zmp tends to overestimate surface rainfall and Zmp is more appropriate for rainfall retrieval. A hybrid technique using a weight between the two rain intensities is testedand found potentially useful for future applications. The estimated surface rain-rate map based on this hybrid approach captures many of the details of the cloud model rain field but still slightly underestimates the rain-rate maximum.
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Zhang, Sidou, Shiyin Liu, and Tengfei Zhang. "Analysis on the Evolution and Microphysical Characteristics of Two Consecutive Hailstorms in Spring in Yunnan, China." Atmosphere 12, no. 1 (January 2, 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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Hartung, Daniel C., Justin M. Sieglaff, Lee M. Cronce, and Wayne F. Feltz. "An Intercomparison of UW Cloud-Top Cooling Rates with WSR-88D Radar Data." Weather and Forecasting 28, no. 2 (April 1, 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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Wapler, Kathrin, Todd P. Lane, Peter T. May, Christian Jakob, Michael J. Manton, and 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, no. 1 (January 1, 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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Bouniol, Dominique, Rémy Roca, Thomas Fiolleau, and D. Emmanuel Poan. "Macrophysical, Microphysical, and Radiative Properties of Tropical Mesoscale Convective Systems over Their Life Cycle." Journal of Climate 29, no. 9 (April 22, 2016): 3353–71. http://dx.doi.org/10.1175/jcli-d-15-0551.1.
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Abstract Mesoscale convective systems (MCSs) are important drivers of the atmospheric large-scale circulation through their associated diabatic heating profile. Taking advantage of recent tracking techniques, this study investigates the evolution of macrophysical, microphysical, and radiative properties over the MCS life cycle by merging geostationary and polar-orbiting satellite data. These observations are performed in three major convective areas: continental West Africa, the adjacent Atlantic Ocean, and the open Indian Ocean. MCS properties are also investigated according to internal subregions (convective, stratiform, and nonprecipitating anvil). Continental MCSs show a specific life cycle, with more intense convection at the beginning. Larger and denser hydrometeors are thus found at higher altitudes, as well as up to the cirriform subregion. Oceanic MCSs have more constant reflectivity values, suggesting a less intense convective updraft, but more persistent intensity. A layer of small crystals is found in all subregions, but with a depth that varies according to the MCS subregion and life cycle. Radiative properties are also examined. It appears that the evolution of large and dense hydrometeors tends to control the evolution of the cloud albedo and the outgoing longwave radiation. The impact of dense hydrometeors, detrained from the convective towers, is also seen in the radiative heating profiles, in particular in the shortwave domain. A dipole of cooling near the cloud top and heating near the cloud base is found in the longwave; this cooling intensifies near the end of the life cycle.
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Oertel, Annika, Michael Sprenger, Hanna Joos, Maxi Boettcher, Heike Konow, Martin Hagen, and 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, no. 1 (February 2, 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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Chernokulsky, Alexander, Andrey Shikhov, Yulia Yarinich, and Alexander Sprygin. "An Empirical Relationship among Characteristics of Severe Convective Storms, Their Cloud-Top Properties and Environmental Parameters in Northern Eurasia." Atmosphere 14, no. 1 (January 13, 2023): 174. http://dx.doi.org/10.3390/atmos14010174.
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Severe convective storms that produce tornadoes and straight-line winds usually develop under particular environmental conditions and have specific signatures on the cloud tops associated with intense updrafts. In this study, we performed a comparative analysis of satellite-derived characteristics, with a focus on cloud-top properties, and ERA5-based environmental parameters of convective storms in forested regions of the western part of Northern Eurasia in 2006–2021. The analyzed sample includes 128 different convective storms that produced 138 tornadoes and 143 linear windstorms. We found most tornadoes and linear windstorms are generated by quasi-linear convective storms or supercells. Such supercells form under lower convective instability and precipitable water content compared to those for other types of storms. We found a significant negative correlation of minimum temperature on the storm cloud top with instability parameters. In turn, the longevity of convective storms significantly correlates with wind shear and storm-relative helicity. About half of the tornadoes and 2/3 of linear windstorms are associated with the presence of cloud-top signatures, such as overshooting tops, cold-ring or cold U/V features. The events associated with such signatures are formed under high values of instability parameters. Our results can be used for further analysis of peculiarities of tornado and linear windstorm formation and to enhance the predictability of such severe events, especially in regions with a lack of weather radar coverage.
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Siqueira, José Ricardo, and 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, no. 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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Rickenbach, Thomas, Paul Kucera, Megan Gentry, Larry Carey, Andrew Lare, Ruei-Fong Lin, Belay Demoz, and 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, no. 10 (October 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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MOHANTY, U. C., N. V. SAM, S. DAS, and S. BASU. "A study on the convective structure of the atmosphere over the West Coast of India during ARMEX-I." MAUSAM 56, no. 1 (January 19, 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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Zhou, Y. P., W. K. Tao, A. Y. Hou, W. S. Olson, C. L. Shie, K. M. Lau, M. D. Chou, X. Lin, and 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, no. 12 (December 1, 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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Rasmussen, Kristen L., and Robert A. Houze. "Orogenic Convection in Subtropical South America as Seen by the TRMM Satellite." Monthly Weather Review 139, no. 8 (August 2011): 2399–420. http://dx.doi.org/10.1175/mwr-d-10-05006.1.
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AbstractExtreme orogenic convective storms in southeastern South America are divided into three categories: storms with deep convective cores, storms with wide convective cores, and storms containing broad stratiform regions. Data from the Tropical Rainfall Measuring Mission satellite’s Precipitation Radar show that storms with wide convective cores are the most frequent, tending to originate near the Sierra de Cordoba range. Downslope flow at upper levels caps a nocturnally enhanced low-level jet, thus preventing convection from breaking out until the jet hits a steep slope of terrain, such as the Sierra de Cordoba Mountains or Andean foothills, so that the moist low-level air is lifted enough to release the instability and overcome the cap. This capping and triggering is similar to the way intense convection is released near the northwestern Himalayas. However, the intense storms with wide convective cores over southeastern South America are unlike their Himalayan counterparts in that they exhibit leading-line/trailing-stratiform organization and are influenced by baroclinic troughs more similar to storms east of the Rocky Mountains in the United States. Comparison of South American storms containing wide convective cores with storms in other parts of the world contributes to a global understanding of how major mountain ranges influence precipitating cloud systems.
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MANDAL, J. C., S. R. KALSI, K. VEERARAGHAVAN, and S. R. HALDER. "Some aspects of Bay of Bengal cyclone of 29 January to 4 February 1987." MAUSAM 41, no. 3 (February 24, 2022): 43–52. http://dx.doi.org/10.54302/mausam.v41i3.2721.
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A satellite study of an unusual tropical cyclone is made to, investigate genesis, intensification, movement and the decay over sea. Dvorak technique has been applied for its Intensity analysis. Satellite cloud imagery analysis indicates that initial genesis was spawned by cross equatorial surges and mechanical subsidence occurring in the relatively cloud free area between deep layer convective cloud masses. Subsequent intensification was favoured by high sea surface temperature and suitable synoptic settings. It appears that initial movement of the vortex was guided by b-effect and subsequent movement by its environmental steering current. New convective cloud mass growth was observed in the direction of its movement and during change of its direction of movement, its speed became slow or it remained stationary for some time. Presence of dry slot in western and southwestern side in its intense stage and elongation of associated cloud mass northeastwards towards the later part of its life indicate its increasing interaction with subtropical westerly flow. This finally led to its dissipation right over sea where sea surface temperature was also relatively less.
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Hagos, Samson, Zhe Feng, Sally McFarlane, and L. Ruby Leung. "Environment and the Lifetime of Tropical Deep Convection in a Cloud-Permitting Regional Model Simulation." Journal of the Atmospheric Sciences 70, no. 8 (August 1, 2013): 2409–25. http://dx.doi.org/10.1175/jas-d-12-0260.1.
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Abstract By applying a cloud-tracking algorithm to tropical convective systems in a regional high-resolution model simulation, this study documents the environmental conditions before and after convective systems are initiated over ocean and land by following them during their lifetime. The comparative roles of various mechanisms of convection–environment interaction on the longevity of convective systems are quantified. The statistics of lifetime, maximum area, and propagation speed of the simulated deep convection agree well with geostationary satellite observations. Among the environmental variables considered, lifetime of convective systems is found to be most related to midtropospheric moisture before as well as after the initiation of convection. Over ocean, convective systems enhance surface fluxes through the associated cooling and drying of the boundary layer as well as increased wind gusts. This process appears to play a minor positive role in the longevity of systems. For systems of equal lifetime, those over land tend to be more intense than those over ocean especially during the early stages of their life cycle. Both over ocean and land, convection is found to transport momentum vertically to increase low-level shear and decrease upper-level shear, but no discernible effect of shear on the lifetime of the convective systems is found.
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Xu, Weixin, Robert F. Adler, and Nai-Yu Wang. "Improving Geostationary Satellite Rainfall Estimates Using Lightning Observations: Underlying Lightning–Rainfall–Cloud Relationships." Journal of Applied Meteorology and Climatology 52, no. 1 (January 2013): 213–29. http://dx.doi.org/10.1175/jamc-d-12-040.1.
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AbstractThis study quantifies the relationships among lightning activity, convective rainfall, and associated cloud properties on both convective-system scale (or storm scale) and satellite-pixel scale (~5 km) on the basis of 13 yr of Tropical Rainfall Measuring Mission measurements of rainfall, lightning, and clouds. Results show that lightning frequency is a good proxy to separate storms of different intensity, identify convective cores, and screen out false convective-core signatures in areas of thick anvil debris. Significant correlations are found between storm-scale lightning parameters and convective rainfall for systems over the southern United States, the focus area of the study. Storm-scale convective rainfall or heavy-precipitation area has the best correlation (coefficient r = 0.75–0.85) with lightning-flash area. It also increases linearly with increasing lightning-flash rate, although correlations between convective/heavy rainfall and lightning-flash rate are somewhat weaker (r = 0.55–0.75). Statistics further show that active lightning and intense precipitation are not well collocated on the pixel scale (5 km); for example, only 50% of the lightning flashes are coincident with heavy-rain cores, and more than 20% are distributed in light-rain areas. Simple positive correlations between lightning-flash rate and precipitation intensity are weak on the pixel scale. Lightning frequency and rain intensity have positive probabilistic relationships, however: the probability of heavy precipitation, especially on a coarser pixel scale (~20 km), increases with increasing lightning-flash density. Therefore, discrete thresholds of lightning density could be applied in a rainfall estimation scheme to assign precipitation in specific rate categories.
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Mazarakis, N., V. Kotroni, K. Lagouvardos, A. A. Argiriou, and C. J. Anderson. "The sensitivity of warm period precipitation forecasts to various modifications of the Kain-Fritsch Convective Parameterization scheme." Natural Hazards and Earth System Sciences 11, no. 5 (May 12, 2011): 1327–39. http://dx.doi.org/10.5194/nhess-11-1327-2011.
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Abstract. The sensitivity of quantitative precipitation forecasts to various modifications of the Kain-Fritsch (KF) convective parameterization scheme (CPS) is examined for twenty selected cases characterized by intense convective activity and widespread precipitation over Greece, during the warm period of 2005–2007. The study is conducted using the MM5 model with a two nested domains strategy, with horizontal grid increments of 24 and 8 km, respectively. Five modifications to the KF CPS, each designed to test the sensitivity of the model to the convective scheme formulation, are discussed. The modifications include: (i) the maximization of the convective scheme precipitation efficiency, (ii) the change of the convective time step, (iii) the forcing of the convective scheme to produce more/less cloud material, (iv) changes to the trigger function and (v) the alteration of the vertical profile of updraft mass flux detrainment. The simulated precipitation from the 8-km grid is verified against raingauge measurements. Although skill scores vary widely among the cases and the precipitation thresholds, model results using the modifications of the convective scheme show improvements in 6-h precipitation totals compared to simulations generated using the unmodified convective scheme. In general, forcing the model to produce less cloud material improves the precipitation forecast for the moderate and high precipitation amounts, while the same modification and the change of the convective time step to 1 min has the same result for the high precipitation thresholds. The increase of convective time step to 15 min, the maximization of precipitation efficiency and the changes to the trigger function give similar results for medium and high precipitation. On the other hand, the forecast for the light precipitation is improved by forcing the model to produce more cloud material as well as by the alteration of the vertical profile of updraft mass flux detrainment.
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Drofa, A. S., V. N. Ivanov, D. Rosenfeld, and A. G. Shilin. "Studying an effect of salt powder seeding used for precipitation enhancement from convective clouds." Atmospheric Chemistry and Physics Discussions 10, no. 4 (April 23, 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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Halverson, J., M. Black, S. Braun, D. Cecil, M. Goodman, A. Heymsfield, G. Heymsfield, et al. "Nasa's Tropical Cloud Systems and Processes Experiment." Bulletin of the American Meteorological Society 88, no. 6 (June 1, 2007): 867–82. http://dx.doi.org/10.1175/bams-88-6-867.
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In July 2005, the National Aeronautics and Space Administration investigated tropical cyclogenesis, hurricane structure, and intensity change in the eastern North Pacific and western Atlantic using its ER-2 high-altitude research aircraft. The campaign, called the Tropical Cloud Systems and Processes (TCSP) experiment, was conducted in conjunction with the National Oceanic and Atmospheric Administration/Hurricane Research Division's Intensity Forecasting Experiment. A number of in situ and remote sensor datasets were collected inside and above four tropical cyclones representing a broad spectrum of tropical cyclone intensity and development in diverse environments. While the TCSP datasets directly address several key hypotheses governing tropical cyclone formation, including the role of vertical wind shear, dynamics of convective bursts, and upscale growth of the initial vortex, two of the storms sampled were also unusually strong, early season storms. Highlights from the genesis missions are described in this article, along with some of the unexpected results from the campaign. Interesting observations include an extremely intense, highly electrified convective tower in the eyewall of Hurricane Emily and a broad region of mesoscale subsidence detected in the lower stratosphere over landfalling Tropical Storm Gert.
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Thayer-Calder, Katherine, and David A. Randall. "The Role of Convective Moistening in the Madden–Julian Oscillation." Journal of the Atmospheric Sciences 66, no. 11 (November 1, 2009): 3297–312. http://dx.doi.org/10.1175/2009jas3081.1.
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Abstract This study compares two models that differ primarily in their cloud parameterizations and produce extremely different simulations of the Madden–Julian oscillation (MJO). The Community Atmosphere Model (CAM) version 3.0 from NCAR uses the Zhang–McFarlane scheme for deep convection and does not produce an MJO. The “superparameterized” version of the CAM (SP-CAM) replaces the cloud parameterizations with a two-dimensional cloud-resolving model (CRM) in each grid column and produces an extremely vigorous MJO. This analysis shows that the CAM is unable to produce high-humidity regions in the mid- to lower troposphere because of a lack of coupling between parameterized convection and environmental relative humidity. The SP-CAM produces an overly moist column due in part to excessive near-surface winds and evaporation during strong convective events. In the real tropics and the SP-CAM, convection within a high-humidity environment produces intense latent heating, which excites the large-scale circulation that is the signature of the MJO. The authors suggest that a model must realistically represent convective processes that moisten the entire tropical troposphere in order to produce a simulation of the MJO.
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Drofa, A. S., V. N. Ivanov, D. Rosenfeld, and A. G. Shilin. "Studying an effect of salt powder seeding used for precipitation enhancement from convective clouds." Atmospheric Chemistry and Physics 10, no. 16 (August 27, 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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Wall, Christina, Edward Zipser, and Chuntao Liu. "An Investigation of the Aerosol Indirect Effect on Convective Intensity Using Satellite Observations." Journal of the Atmospheric Sciences 71, no. 1 (December 27, 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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Singh, Martin S., Zhiming Kuang, Eric D. Maloney, Walter M. Hannah, and Brandon O. Wolding. "Increasing potential for intense tropical and subtropical thunderstorms under global warming." Proceedings of the National Academy of Sciences 114, no. 44 (October 16, 2017): 11657–62. http://dx.doi.org/10.1073/pnas.1707603114.
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Intense thunderstorms produce rapid cloud updrafts and may be associated with a range of destructive weather events. An important ingredient in measures of the potential for intense thunderstorms is the convective available potential energy (CAPE). Climate models project increases in summertime mean CAPE in the tropics and subtropics in response to global warming, but the physical mechanisms responsible for such increases and the implications for future thunderstorm activity remain uncertain. Here, we show that high percentiles of the CAPE distribution (CAPE extremes) also increase robustly with warming across the tropics and subtropics in an ensemble of state-of-the-art climate models, implying strong increases in the frequency of occurrence of environments conducive to intense thunderstorms in future climate projections. The increase in CAPE extremes is consistent with a recently proposed theoretical model in which CAPE depends on the influence of convective entrainment on the tropospheric lapse rate, and we demonstrate the importance of this influence for simulated CAPE extremes using a climate model in which the convective entrainment rate is varied. We further show that the theoretical model is able to account for the climatological relationship between CAPE and a measure of lower-tropospheric humidity in simulations and in observations. Our results provide a physical basis on which to understand projected future increases in intense thunderstorm potential, and they suggest that an important mechanism that contributes to such increases may be present in Earth’s atmosphere.
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Mullendore, Gretchen Louise, and Mariusz Starzec. "Forecast Model Activities for North Dakota Cloud Modification Project." Journal of Weather Modification 48, no. 1 (April 30, 2016): 93–98. http://dx.doi.org/10.54782/jwm.v48i1.546.
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An overview of regional forecast simulations in support of North Dakota Cloud Modification Project (NDCMP) operations is presented. Simulations are run twice daily during the summer season by University of North Dakota. Object-based verification of observed and simulated radar reflectivity is conducted during the off-season. Verification of seasonal performance allows modifications to forecast simulations focused on improving operations for the North Dakota region. NDCMP simulated forecasts are found to biased towards too many convective objects and convection that is too intense and too large. Case studies showed that a change in microphysical scheme and adjustments to cloud droplet concentration lessened the biases.
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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, and YU I. YARINICH. "ATMOSPHERIC SEVERE CONVECTIVE EVENTS IN RUSSIA: CHANGES OBSERVED FROM DIFFERENT DATA." Meteorologiya i Gidrologiya, no. 5 (May 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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Slawinska, Joanna, Olivier Pauluis, Andrew J. Majda, and Wojciech W. Grabowski. "Multiscale Interactions in an Idealized Walker Cell: Simulations with Sparse Space–Time Superparameterization." Monthly Weather Review 143, no. 2 (February 1, 2015): 563–80. http://dx.doi.org/10.1175/mwr-d-14-00082.1.
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Abstract This paper discusses the sparse space–time superparameterization (SSTSP) algorithm and evaluates its ability to represent interactions between moist convection and the large-scale circulation in the context of a Walker cell flow over a planetary scale two-dimensional domain. The SSTSP represents convective motions in each column of the large-scale model by embedding a cloud-resolving model, and relies on a sparse sampling in both space and time to reduce computational cost of explicit simulation of convective processes. Simulations are performed varying the spatial compression and/or temporal acceleration, and results are compared to the cloud-resolving simulation reported previously. The algorithm is able to reproduce a broad range of circulation features for all temporal accelerations and spatial compressions, but significant biases are identified. Precipitation tends to be too intense and too localized over warm waters when compared to the cloud-resolving simulations. It is argued that this is because coherent propagation of organized convective systems from one large-scale model column to another is difficult when superparameterization is used, as noted in previous studies. The Walker cell in all simulations exhibits low-frequency variability on a time scale of about 20 days, characterized by four distinctive stages: suppressed, intensification, active, and weakening. The SSTSP algorithm captures spatial structure and temporal evolution of the variability. This reinforces the confidence that SSTSP preserves fundamental interactions between convection and the large-scale flow, and offers a computationally efficient alternative to traditional convective parameterizations.
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Klein, Cornelia, Francis Nkrumah, Christopher M. Taylor, and Elijah A. Adefisan. "Seasonality and Trends of Drivers of Mesoscale Convective Systems in Southern West Africa." Journal of Climate 34, no. 1 (January 2021): 71–87. http://dx.doi.org/10.1175/jcli-d-20-0194.1.
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AbstractMesoscale convective systems (MCSs) are the major source of extreme rainfall over land in the tropics and are expected to intensify with global warming. In the Sahel, changes in surface temperature gradients and associated changes in wind shear have been found to be important for MCS intensification in recent decades. Here we extend that analysis to southern West Africa (SWA) by combining 34 years of cloud-top temperatures with rainfall and reanalysis data. We identify clear trends in intense MCSs since 1983 and their associated atmospheric drivers. We also find a marked annual cycle in the drivers, linked to changes in the convective regime during the progression of the West African monsoon. Before the peak of the first rainy season, we identify a shear regime where increased temperature gradients play a crucial role for MCS intensity trends. From June onward, SWA moves into a less unstable, moist regime during which MCS trends are mainly linked to frequency increase and may be more influenced by total column water vapor. However, during both seasons we find that MCSs with the most intense convection occur in an environment with stronger wind shear, increased low-level humidity, and drier midlevels. Comparing the sensitivity of MCS intensity and peak rainfall to low-level moisture and wind shear conditions preceding events, we find a dominant role for wind shear. We conclude that MCS trends are directly linked to a strengthening of two distinct convective regimes that cause the seasonal change of SWA MCS characteristics. However, the convective environment that ultimately produces the most intense MCSs remains the same.
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Aumann, H. H., and S. G. DeSouza-Machado. "Deep convective clouds at the tropopause." Atmospheric Chemistry and Physics Discussions 10, no. 7 (July 2, 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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Zavolgenskiy, M. V., and P. B. Rutkevich. "Tornado funnel-shaped cloud as convection in a cloudy layer." Advances in Science and Research 3, no. 1 (April 2, 2009): 17–21. http://dx.doi.org/10.5194/asr-3-17-2009.
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Abstract. Analytical model of convection in a thick horizontal cloud layer with free upper and lower boundaries is constructed. The cloud layer is supposed to be subjected to the Coriolis force due to the cloud rotation, which is a typical condition for tornado formation. It is obtained that convection in such system can look as just one rotating cell in contrast to the usual many-cells Benard convection. The tornado-type vortex is different from spatially periodic convective cells because their amplitudes vanish with distance from the vortex axis. The lower boundary at this convection can substantially move out of the initially horizontal cloud layer forming a single vertical vortex with intense upward and downward flows. The results are also applicable to convection in water layer with negative temperature gradient.
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Grell, G., S. R. Freitas, M. Stuefer, and J. Fast. "Inclusion of biomass burning in WRF-Chem: impact of wildfires on weather forecasts." Atmospheric Chemistry and Physics 11, no. 11 (June 6, 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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Varble, Adam C., Stephen W. Nesbitt, Paola Salio, Joseph C. Hardin, Nitin Bharadwaj, Paloma Borque, Paul J. DeMott, et al. "Utilizing a Storm-Generating Hotspot to Study Convective Cloud Transitions: The CACTI Experiment." Bulletin of the American Meteorological Society 102, no. 8 (August 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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Grant, Leah D., Todd P. Lane, and Susan C. van den Heever. "The Role of Cold Pools in Tropical Oceanic Convective Systems." Journal of the Atmospheric Sciences 75, no. 8 (July 20, 2018): 2615–34. http://dx.doi.org/10.1175/jas-d-17-0352.1.
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Abstract The processes governing organized tropical convective systems are not completely understood despite their important influences on the tropical atmosphere and global circulation. In particular, cold pools are known to influence the structure and maintenance of midlatitude systems via Rotunno–Klemp–Weisman (RKW) theory, but cold pools may interact differently with tropical convection because of differences in cold pool strength and environmental shear. In this study, the role of cold pools in organized oceanic tropical convective systems is investigated, including their influence on system intensity, mesoscale structure, and propagation. To accomplish this goal, high-resolution idealized simulations are performed for two different systems that are embedded within a weakly sheared cloud population approaching radiative–convective equilibrium. The cold pools are altered by changing evaporation rates below cloud base in a series of sensitivity tests. The simulations demonstrate surprising findings: when cold pools are weakened, the convective systems become more intense. However, their propagation speeds and mesoscale structure are largely unaffected by the cold pool changes. Passive tracers introduced into the cold pools indicate that the convection intensifies when cold pools are weakened because cold pool air is entrained into updrafts, thereby reducing updraft intensity via the cold pools’ initial negative buoyancy. Gravity waves, rather than cold pools, appear to be the important modulators of system propagation and mesoscale structure. These results reconfirm that RKW theory does not fully explain the behavior of tropical oceanic convective systems, even those that otherwise appear consistent with RKW thinking.
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Wang, Chun-Chih, and Daniel J. Kirshbaum. "Thermally Forced Convection over a Mountainous Tropical Island." Journal of the Atmospheric Sciences 72, no. 6 (May 27, 2015): 2484–506. http://dx.doi.org/10.1175/jas-d-14-0325.1.
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Abstract Observations from the Dominica Experiment (DOMEX) and cloud-resolving numerical simulations are used to study a thermally forced convection event over the Caribbean island of Dominica on 18 April 2011. A clear diurnal cycle of island thermal forcing and cumulus convection was observed, with cumuli initiating over the southwestern flank of the ridge and deepening as they drifted eastward. Apart from errors in cloud fraction and (notably) precipitation, the simulations verified well against the observations, provided horizontal grid spacings of 500 m or less were used. The simulated flows developed an island-scale solenoidal circulation with an organized and intense updraft over the ridge that focused convective initiation. Sensitivity tests investigated the impacts of topographic forcing, subcloud winds, and cloud–radiative feedbacks on the island-scale horizontal inflow and cloud vertical mass flux. These experiments confirmed that thermal forcing drove the island convection and that the inflow and cloud mass flux were maximized under weak ambient cross-island winds. The simulations also indicated that cloud shading and precipitation each reduced the island inflow by ~20% while cloud latent heat release enhanced it by ~20%. However, precipitation caused a much smaller reduction in cloud mass flux (10%) than did cloud shading (50%) owing to effective secondary convective initiation by subcloud cold pools. Thermodynamic heat-engine theory provided accurate predictions of the simulated solenoidal updraft magnitudes in selected cases. It also provided a simple explanation for the weakening of the simulated thermal circulation in the presence of island orography: a shallower mixed layer reduced the efficiency of the thermal circulation.
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Herbert, Ross, and Philip Stier. "Satellite observations of smoke–cloud–radiation interactions over the Amazon rainforest." Atmospheric Chemistry and Physics 23, no. 7 (April 17, 2023): 4595–616. http://dx.doi.org/10.5194/acp-23-4595-2023.
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Abstract. The Amazon rainforest routinely experiences intense and long-lived biomass burning events that result in smoke plumes that cover vast regions. The spatial and temporal extent of the plumes and the complex pathways through which they interact with the atmosphere have proved challenging to measure for purposes of gaining a representative understanding of smoke impacts on the Amazonian atmosphere. In this study, we use multiple collocated satellite sensors on board AQUA and TERRA platforms to study the underlying smoke–cloud–radiation interactions during the diurnal cycle. An 18-year time series for both morning and afternoon overpasses is constructed, providing collocated measurements of aerosol optical depth (AOD; column-integrated aerosol extinction), cloud properties, top-of-atmosphere radiative fluxes, precipitation, and column water vapour content from independent sources. The long-term time series reduces the impact of interannual variability and provides robust evidence that smoke significantly modifies the Amazonian atmosphere. Low loadings of smoke (AOD ≤ 0.4) enhance convective activity, cloudiness, and precipitation, but higher loadings (AOD > 0.4) strongly suppress afternoon convection and promote low-level cloud occurrence. Accumulated precipitation increases with convective activity but remains elevated under high smoke loadings, suggesting fewer but more intense convective cells. Contrasting morning and afternoon cloud responses to smoke are observed, in line with recent simulations. Observations of top-of-atmosphere radiative fluxes support the findings and show that the response of low-level cloud properties and cirrus coverage to smoke results in a pronounced and consistent increase in top-of-atmosphere outgoing radiation (cooling) of up to 50 W m−2 for an AOD perturbation of +1.0. The results demonstrate that smoke strongly modifies the atmosphere over the Amazon via widespread changes to the cloud field properties. Rapid adjustments work alongside instantaneous radiative effects to drive a stronger cooling effect from smoke than previously thought, whilst contrasting morning and afternoon responses of liquid and ice water paths highlight a potential method for constraining aerosol impacts on climate. Increased drought susceptibility, land use change, and deforestation will have important and widespread impacts on the region over the coming decades. Based on this analysis, we anticipate that further increases in anthropogenic fire activity will associated with an overall reduction in regional precipitation and a negative forcing (cooling) on the Earth's energy budget.
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Braun, Scott A., Michael T. Montgomery, Kevin J. Mallen, and Paul D. Reasor. "Simulation and Interpretation of the Genesis of Tropical Storm Gert (2005) as Part of the NASA Tropical Cloud Systems and Processes Experiment." Journal of the Atmospheric Sciences 67, no. 4 (April 1, 2010): 999–1025. http://dx.doi.org/10.1175/2009jas3140.1.
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Abstract Several hypotheses have been put forward for the mechanisms of generation of surface circulation associated with tropical cyclones. This paper examines high-resolution simulations of Tropical Storm Gert (2005), which formed in the Gulf of Mexico during NASA’s Tropical Cloud Systems and Processes Experiment, to investigate the development of low-level circulation and its relationship to the precipitation evolution. Two simulations are examined: one that better matches available observations but underpredicts the storm’s minimum sea level pressure and a second one that somewhat overintensifies the storm but provides a set of simulations that encapsulates the overall genesis and development characteristics of the observed storm. The roles of convective and stratiform precipitation processes within the mesoscale precipitation systems that formed Gert are discussed. During 21–25 July, two episodes of convective system development occurred. In each, precipitation system evolution was characterized by intense and deep convective upward motions followed by increasing stratiform-type vertical motions (upper-level ascent, low-level descent). Potential vorticity (PV) in convective regions was strongest at low levels while stratiform-region PV was strongest at midlevels, suggesting that convective processes acted to spin up lower levels prior to the spinup of middle levels by stratiform processes. Intense vortical hot towers (VHTs) were prominent features of the low-level cyclonic vorticity field. The most prominent PV anomalies persisted more than 6 h and were often associated with localized minima in the sea level pressure field. A gradual aggregation of the cyclonic PV occurred as existing VHTs near the center continually merged with new VHTs, gradually increasing the mean vorticity near the center. Nearly concurrently with this VHT-induced development, stratiform precipitation processes strongly enhanced the mean inflow and convergence at middle levels, rapidly increasing the midlevel vorticity. However, the stratiform vertical motion profile is such that while it increases midlevel vorticity, it decreases vorticity near the surface as a result of low-level divergence. Consequently, the results suggest that while stratiform precipitation regions may significantly increase cyclonic circulation at midlevels, convective vortex enhancement at low to midlevels is likely necessary for genesis.
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Sieglaff, Justin M., Lee M. Cronce, and Wayne F. Feltz. "Improving Satellite-Based Convective Cloud Growth Monitoring with Visible Optical Depth Retrievals." Journal of Applied Meteorology and Climatology 53, no. 2 (February 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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Lane, Todd P., and 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, no. 11 (November 1, 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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Matsui, Toshi, Brenda Dolan, Takamichi Iguchi, Steven A. Rutledge, Wei-Kuo Tao, and Stephen Lang. "Polarimetric Radar Characteristics of Simulated and Observed Intense Convective Cores for a Midlatitude Continental and Tropical Maritime Environment." Journal of Hydrometeorology 21, no. 3 (March 2020): 501–17. http://dx.doi.org/10.1175/jhm-d-19-0185.1.
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AbstractThis study contrasts midlatitude continental and tropical maritime deep convective cores using polarimetric radar observables and retrievals from selected deep convection episodes during the MC3E and TWPICE field campaigns. The continental convective cores produce stronger radar reflectivities throughout the profiles, while maritime convective cores produce more positive differential reflectivity Zdr and larger specific differential phase Kdp above the melting level. Hydrometeor identification retrievals revealed the presence of large fractions of rimed ice particles (snow aggregates) in the continental (maritime) convective cores, consistent with the Zdr and Kdp observations. The regional cloud-resolving model simulations with bulk and size-resolved bin microphysics are conducted for the selected cases, and the simulation outputs are converted into polarimetric radar signals and retrievals identical to the observational composites. Both the bulk and the bin microphysics reproduce realistic land and ocean (L-O) contrasts in reflectivity, polarimetric variables of rain drops, and hydrometeor profiles, but there are still large uncertainties in describing Zdr and Kdp of ice crystals associated with the ice particle shapes/orientation assumptions. Sensitivity experiments are conducted by swapping background aerosols between the continental and maritime environments, revealing that background aerosols play a role in shaping the distinct L-O contrasts in radar reflectivity associated with raindrop sizes, in addition to the dominant role of background thermodynamics.
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Siqueira, Jose Ricardo, William B. Rossow, Luiz Augusto Toledo Machado, and Cindy Pearl. "Structural Characteristics of Convective Systems over South America Related to Cold-Frontal Incursions." Monthly Weather Review 133, no. 5 (May 1, 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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Vendrasco, Eder P., Luiz A. T. Machado, Bruno Z. Ribeiro, Edmilson D. Freitas, Rute C. Ferreira, and Renato G. Negri. "Cloud-Resolving Model Applied to Nowcasting: An Evaluation of Radar Data Assimilation and Microphysics Parameterization." Weather and Forecasting 35, no. 6 (December 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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Seifert, Axel, Alexander Khain, Ulrich Blahak, and 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, no. 6 (June 1, 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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SHIVHARE, R. P. "Episodes of aircraft icing during ARMEX phase-I." MAUSAM 56, no. 1 (January 19, 2022): 83–88. http://dx.doi.org/10.54302/mausam.v56i1.865.
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In-flight icing is one of the major weather hazards to aviation. During ARMEX Phase-I, there were three occasions out of twenty sorties when in-flight icing was encountered while flying over Arabian Sea in the Russian made transport aircraft AN-32. The icing episodes were studied vis-à-vis the prevailing synoptic situations and the convective cloud features. It was found that the aircraft was flying in the vicinity of convective cells associated with considerable horizontal wind shear. The temperature at the flight level was observed to vary from -6 to -8° C. The presence of large amount of supercooled water droplets can be assumed to be associated with the active and intense convection that is usually found under the active monsoon conditions.
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Besson, L., and Y. Lemaître. "Mesoscale Convective Systems in Relation to African and Tropical Easterly Jets." Monthly Weather Review 142, no. 9 (September 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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Johnston, M. S., S. Eliasson, P. Eriksson, R. M. Forbes, A. Gettelman, P. Räisänen, and M. D. Zelinka. "Diagnosing the average spatio-temporal impact of convective systems – Part 2: A model intercomparison using satellite data." Atmospheric Chemistry and Physics 14, no. 16 (August 26, 2014): 8701–21. http://dx.doi.org/10.5194/acp-14-8701-2014.
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Abstract. The representation of the effect of tropical deep convective (DC) systems on upper-tropospheric moist processes and outgoing longwave radiation is evaluated in the EC-Earth3, ECHAM6, and CAM5 (Community Atmosphere Model) climate models using satellite-retrieved data. A composite technique is applied to thousands of deep convective systems that are identified using local rain rate maxima in order to focus on the temporal evolution of the deep convective processes in the model and satellite-retrieved data. The models tend to over-predict the occurrence of rain rates that are less than ≈ 3 mm h−1 compared to Tropical Rainfall Measurement Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA). While the diurnal distribution of oceanic rain rate maxima in the models is similar to the satellite-retrieved data, the land-based maxima are out of phase. Despite having a larger climatological mean upper-tropospheric relative humidity, models closely capture the satellite-derived moistening of the upper troposphere following the peak rain rate in the deep convective systems. Simulated cloud fractions near the tropopause are larger than in the satellite data, but the ice water contents are smaller compared with the satellite-retrieved ice data. The models capture the evolution of ocean-based deep convective systems fairly well, but the land-based systems show significant discrepancies. Over land, the diurnal cycle of rain is too intense, with deep convective systems occurring at the same position on subsequent days, while the satellite-retrieved data vary more in timing and geographical location. Finally, simulated outgoing longwave radiation anomalies associated with deep convection are in reasonable agreement with the satellite data, as well as with each other. Given the fact that there are strong disagreements with, for example, cloud ice water content, and cloud fraction, between the models, this study supports the hypothesis that such agreement with satellite-retrieved data is achieved in the three models due to different representations of deep convection processes and compensating errors.
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Hu, Jiaxi, Daniel Rosenfeld, Alexander Ryzhkov, and 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, no. 6 (June 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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Johnston, M. S., S. Eliasson, P. Eriksson, R. M. Forbes, A. Gettelman, P. Räisänen, and M. D. Zelinka. "Diagnosing the average spatio-temporal impact of convective systems – Part 2: A model inter-comparison using satellite data." Atmospheric Chemistry and Physics Discussions 14, no. 7 (April 4, 2014): 9155–201. http://dx.doi.org/10.5194/acpd-14-9155-2014.
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Abstract. The representation of the effect of tropical deep convective (DC) systems on upper-tropospheric moist processes and outgoing longwave radiation (OLR) is evaluated in the climate models EC-Earth, ECHAM6, and CAM5 using satellite observations. A composite technique is applied to thousands of deep convective systems that are identified using local rain rate (RR) maxima in order to focus on the temporal evolution of the deep convective processes in the model and observations. The models tend to over-produce rain rates less than about 3 mm h−1 and underpredict the occurrence of more intense rain. While the diurnal distribution of oceanic rain rate maxima in the models is similar to the observations, the land-based maxima are out of phase. Over land, the diurnal cycle of rain is too intense, with DC events occurring at the same position on subsequent days, while the observations vary more in timing and geographical location. Despite having a larger climatological mean upper tropospheric relative humidity, models closely capture the observed moistening of the upper troposphere following the peak rain rate in the deep convective systems. A comparison of the evolution of vertical profiles of ice water content and cloud fraction shows significant differences between models and with the observations. Simulated cloud fractions near the tropopause are also larger than observed, but the corresponding ice water contents are smaller compared to the observations. EC-Earth's CF at pressure levels > 300 hPa are generally less than the obervations while the other models tend to have larger CF for similar altitudes. The models' performance for ocean-based systems seems to capture the evolution of DC systems fairly well, but the land-based systems show significant discrepancies. In particular, the models have a significantly stronger diurnal cycle at the same geo-spatial position. Finally, OLR anomalies associated with deep convection are in reasonable agreement with the observations. This study shows that such agreement with observations can be achieved in different ways in the three models due to different representations of deep convection processes and compensating errors.
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Klein, Cornelia, Emily R. Potter, Cornelia Zauner, Wolfgang Gurgiser, Rolando Cruz Encarnación, Alejo Cochachín Rapre, and Fabien Maussion. "Farmers’ first rain: investigating dry season rainfall characteristics in the Peruvian Andes." Environmental Research Communications 5, no. 7 (July 1, 2023): 071004. http://dx.doi.org/10.1088/2515-7620/ace516.
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Abstract In the Peruvian Andes, the first light rainfalls towards the end of the dry season in August-September are known as pushpa. Softening soils and improving sowing conditions, these rains are crucial for planting dates and agricultural planning. Yet pushpa remains to date unexplored in the literature. This study uses observations and convection-permitting model simulations to describe the characteristics of pushpa in the Rio Santa valley (Peru). Comparing an observed pushpa case in August 2018 with a dry and wet event of the same season, we find pushpa to coincide with upper-level westerly winds that are otherwise characteristic for dry periods. These conditions impose an upper-level dry layer that favours small-scale, vertically-capped convection, explaining the low rainfall intensities that are reportedly typical for pushpa. Climatologically, we find 83% of pushpa-type events to occur under westerly winds, dominating in August, when 60% of the modelled spatial rainfall extent is linked to pushpa. Larger, more intense deep-convective events gradually increase alongside more easterly winds in September, causing the relative pushpa cloud coverage to drop to ̃20%. We note high inter-annual and -decadal variability in this balance between pushpa and intense convective rainfall types, with the spatial extent of pushpa rainfall being twice as high during 2000-2009 than for the 2010-2018 decade over the key sowing period. This result may explain farmers’ perception in the Rio Santa valley, who recently reported increased challenges due to delayed but more intense pushpa rains before the rainy season start. We thus conclude that the sowing and germination season is crucially affected by the balance of pushpa-type and deep-convective rain, resulting in a higher probability for late first rains to be more intense.