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Fritsch, J. Michael. "Modification of Mesoscale Convective Weather Systems". Meteorological Monographs 43 (1.12.1986): 77–86. http://dx.doi.org/10.1175/0065-9401-21.43.77.
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Abstract Modification of mesoscale convective weather systems through ice-phase seeding is briefly reviewed. a simple mathematical framework for estimating the likely mesoscale response to convective cloud modification is presented, and previous mesoscale modification hypotheses are discussed in the context of this mathematical framework. Some basic differences between cloud-scale and mesoscale modification hypotheses are also discussed. Numerical model experiments to test the mesoscale sensitivity of convective weather systems are reviewed, and several focal points for identifying mesoscale modification potential are presented.
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Moncrieff, Mitchell W., i Changhai Liu. "Representing Convective Organization in Prediction Models by a Hybrid Strategy". Journal of the Atmospheric Sciences 63, nr 12 (grudzień 2006): 3404–20. http://dx.doi.org/10.1175/jas3812.1.
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The mesoscale organization of precipitating convection is highly relevant to next-generation global numerical weather prediction models, which will have an intermediate horizontal resolution (grid spacing about 10 km). A primary issue is how to represent dynamical mechanisms that are conspicuously absent from contemporary convective parameterizations. A hybrid parameterization of mesoscale convection is developed, consisting of convective parameterization and explicit convectively driven circulations. This kind of problem is addressed for warm-season convection over the continental United States, although it is argued to have more general application. A hierarchical strategy is adopted: cloud-system-resolving model simulations represent the mesoscale dynamics of convective organization explicitly and intermediate resolution simulations involve the hybrid approach. Numerically simulated systems are physically interpreted by a mechanistic dynamical model of organized propagating convection. This model is a formal basis for approximating mesoscale convective organization (stratiform heating and mesoscale downdraft) by a first-baroclinic heating couplet. The hybrid strategy is implemented using a predictor–corrector strategy. Explicit dynamics is the predictor and the first-baroclinic heating couplet the corrector. The corrector strengthens the systematically weak mesoscale downdrafts that occur at intermediate resolution. When introduced to the Betts–Miller–Janjic convective parameterization, this new hybrid approach represents the propagation and dynamical structure of organized precipitating systems. Therefore, the predictor–corrector hybrid approach is an elementary practical framework for representing organized convection in models of intermediate resolution.
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Lane, Todd P., i Fuqing Zhang. "Coupling between Gravity Waves and Tropical Convection at Mesoscales". Journal of the Atmospheric Sciences 68, nr 11 (1.11.2011): 2582–98. http://dx.doi.org/10.1175/2011jas3577.1.
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Abstract An idealized cloud-system-resolving model simulation is used to examine the coupling between a tropical cloud population and the mesoscale gravity waves that it generates. Spectral analyses of the cloud and gravity wave fields identify a clear signal of coupling between the clouds and a deep tropospheric gravity wave mode with a vertical wavelength that matches the depth of the convection, which is about two-thirds of the tropospheric depth. This vertical wavelength and the period of the waves, defined by a characteristic convective time scale, means that the horizontal wavelength is constrained through the dispersion relation. Indeed, the wave–convection coupling manifests at the appropriate wavelength, with the emergence of quasi-regular cloud-system spacing of order 100 km. It is shown that cloud systems at this spacing achieve a quasi-resonant state, at least for a few convective life cycles. Such regular spacing is a key component of cloud organization and is likely a contributor to the processes controlling the upscale growth of convective systems. Other gravity wave processes are also elucidated, including their apparent role in the maintenance of convective systems by providing a mechanism for renewed convective activity and system longevity.
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Grant, Leah D., Todd P. Lane i Susan C. van den Heever. "The Role of Cold Pools in Tropical Oceanic Convective Systems". Journal of the Atmospheric Sciences 75, nr 8 (20.07.2018): 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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Wei, Junhong, i Fuqing Zhang. "Mesoscale Gravity Waves in Moist Baroclinic Jet–Front Systems". Journal of the Atmospheric Sciences 71, nr 3 (27.02.2014): 929–52. http://dx.doi.org/10.1175/jas-d-13-0171.1.
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Abstract A series of cloud-permitting simulations with the Weather Research and Forecast model (WRF) are performed to study the characteristics and source mechanisms of mesoscale gravity waves in moist baroclinic jet–front systems with varying degrees of convective instability. These idealized experiments are initialized with the same baroclinic jet but with different initial moisture content, which produce different life cycles of moist baroclinic waves, to investigate the relative roles of moist processes and baroclinicity in the generation and propagation of mesoscale gravity waves. The dry experiment with no moisture or convection simulates gravity waves that are consistent with past modeling studies. An experiment with a small amount of moisture produces similar baroclinic life cycles to the dry experiment but with the introduction of weak convective instability. Subsequent initiation of convection, although weak, may considerably amplify the gravity waves that are propagating away from the upper-level jet exit region crossing the ridge to the jet entrance region. The weak convection also generates a new wave mode of shorter-scale wave packets that are believed to interact with, strengthen, and modify the dry gravity wave modes. Further increase of the moisture content (up to 5 times) leads to strong convective instability and vigorous moist convection. Besides a faster-growing moist baroclinic wave, the convectively generated gravity waves emerge much earlier, are more prevalent, and are larger in amplitude; they are fully coupled with, and hardly separable from, the dry gravity wave modes under the complex background moist baroclinic waves.
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Pope, Mick, Christian Jakob i Michael J. Reeder. "Convective Systems of the North Australian Monsoon". Journal of Climate 21, nr 19 (1.10.2008): 5091–112. http://dx.doi.org/10.1175/2008jcli2304.1.
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Abstract The climatology of convection over northern Australia and the surrounding oceans, based on six wet seasons (September–April), is derived from the Japanese Meteorological Agency Geostationary Meteorological Satellite-5 (GMS-5) IR1 channel for the years from 1995/96 to 2000/01. This is the first multiyear study of this kind. Clouds are identified at two cloud-top temperature thresholds: 235 and 208 K. The annual cycle of cloudiness over northern Australia shows an initial (October–November) buildup over the Darwin region before widespread cloudiness develops over the entire region during the monsoon months (December–February), followed by a northward contraction during March and April. Tracking mesoscale convective systems (MCSs) reveals that both the size of the cloud systems and their lifetimes follow power-law distributions. For short-lived MCSs (less than 12 h), the initial expansion of the cloudy area is related to the lifetime, with mergers important for long-lived MCSs (greater than 24 h). During periods of deep zonal flow, which coincide with the active phase of the monsoon, the number of convective elements in the Darwin region peaks in the early afternoon, which is characteristic of the diurnal cycle over land. In contrast, when the zonal flow is deep and easterly and the monsoon is in a break phase, the areal extent of the convective elements in the Darwin region is greatest in the late morning, which is more typical of maritime convection.
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Wapler, Kathrin, Todd P. Lane, Peter T. May, Christian Jakob, Michael J. Manton i Steven T. Siems. "Cloud-System-Resolving Model Simulations of Tropical Cloud Systems Observed during the Tropical Warm Pool-International Cloud Experiment". Monthly Weather Review 138, nr 1 (1.01.2010): 55–73. http://dx.doi.org/10.1175/2009mwr2993.1.
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Abstract Nested cloud-system-resolving model simulations of tropical convective clouds observed during the recent Tropical Warm Pool-International Cloud Experiment (TWP-ICE) are conducted using the Weather Research and Forecasting (WRF) model. The WRF model is configured with a highest-resolving domain that uses 1.3-km grid spacing and is centered over Darwin, Australia. The performance of the model in simulating two different convective regimes observed during TWP-ICE is considered. The first regime is characteristic of the active monsoon, which features widespread cloud cover that is similar to maritime convection. The second regime is a monsoon break, which contains intense localized systems that are representative of diurnally forced continental convection. Many aspects of the model performance are considered, including their sensitivity to physical parameterizations and initialization time, and the spatial statistics of rainfall accumulations and the rain-rate distribution. While the simulations highlight many challenges and difficulties in correctly modeling the convection in the two regimes, they show that provided the mesoscale environment is adequately reproduced by the model, the statistics of the simulated rainfall agrees reasonably well with the observations.
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Besson, L., i Y. Lemaître. "Mesoscale Convective Systems in Relation to African and Tropical Easterly Jets". Monthly Weather Review 142, nr 9 (wrzesień 2014): 3224–42. http://dx.doi.org/10.1175/mwr-d-13-00247.1.
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This paper documents the interaction processes between mesoscale convective systems (MCS), the tropical easterly jet (TEJ), and the African easterly jet (AEJ) over West Africa during the monsoon peak of 2006 observed during the African Monsoon Multidisciplinary Analyses (AMMA) project. The results highlight the importance of the cloud system localization relative to the jets in order to explain their duration and life cycle. A systematical study reveals that intense and long-lived MCSs correspond to a particular pattern where clouds associated with deep convection are located in entrance regions of TEJ and in exit regions of AEJ. A case study on a particularly well-documented convective event characterizes this link and infers the importance of jet streaks in promoting areas of divergence, favoring the persistence of MCSs.
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Mattos, Enrique V., i Luiz A. T. Machado. "Cloud-to-ground lightning and Mesoscale Convective Systems". Atmospheric Research 99, nr 3-4 (marzec 2011): 377–90. http://dx.doi.org/10.1016/j.atmosres.2010.11.007.
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Mathon, Vincent, i Henri Laurent. "Life cycle of Sahelian mesoscale convective cloud systems". Quarterly Journal of the Royal Meteorological Society 127, nr 572 (styczeń 2001): 377–406. http://dx.doi.org/10.1002/qj.49712757208.
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Pope, Mick, Christian Jakob i Michael J. Reeder. "Objective Classification of Tropical Mesoscale Convective Systems". Journal of Climate 22, nr 22 (15.11.2009): 5797–808. http://dx.doi.org/10.1175/2009jcli2777.1.
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Abstract A cluster analysis is applied to the mesoscale convective systems (MCSs) that developed in northern Australia and the surrounding oceans during six wet seasons (September–April) from 1995/96 to 2000/01. During this period, 13 585 MCSs were identified and tracked using an infrared channel (IR1) on the Japanese Meteorological Agency Geostationary Meteorological Satellite 5 (GMS5). Based on the lifetimes of the MCSs, the area covered by cloud, the expansion rate of the cloud, the minimum cloud-top temperature, and their zonal direction of propagation, the MCSs are grouped objectively into four classes. One of the strengths of the analysis is that it objectively condenses a large dataset into a small number of classes, each with its own physical characteristics. MCSs in class 1 (short) are relatively short lived, with 95% having lifetimes less than 5 h, and they are found most frequently over the oceans during the early and late parts of the wet season. MCSs in classes 2 and 3 [long and intermediate west (Int-West)] are longer lived and propagate to the west, developing over continental northwest Australia in deep easterly flow during breaks in the monsoon. These two classes are distinguished principally by their lifetime, with 95% of MCSs in the long class having lifetimes exceeding 4 h. Class 4 (Int-East) comprises MCSs that form over the subtropical latitudes of eastern Australia and in the deep westerly flow over northern parts of the continent during the monsoon and active phases of the MJO.
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Liu, Changhai, i Mitchell W. Moncrieff. "Shear-Parallel Mesoscale Convective Systems in a Moist Low-Inhibition Mei-Yu Front Environment". Journal of the Atmospheric Sciences 74, nr 12 (1.12.2017): 4213–28. http://dx.doi.org/10.1175/jas-d-17-0121.1.
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Abstract Numerical simulations are performed to investigate organized convection observed in the Asian summer monsoon and documented as a category of mesoscale convective systems (MCSs) over the U.S. continent during the warm season. In an idealized low-inhibition and unidirectional shear environment of the mei-yu moisture front, the structure of the simulated organized convection is distinct from that occurring in the classical quasi-two-dimensional, shear-perpendicular, and trailing stratiform (TS) MCS. Consisting of four airflow branches, a three-dimensional, eastward-propagating, downshear-tilted, shear-parallel MCS builds upshear by initiating new convection at its upstream end. The weak cold pool in the low-inhibition environment negligibly affects convection initiation, whereas convectively generated gravity waves are vital. Upstream-propagating gravity waves form a saturated or near-saturated moist tongue, and downstream-propagating waves control the initiation and growth of convection within a preexisting cloud layer. A sensitivity experiment wherein the weak cold pool is removed entirely intensifies the MCS and its interaction with the environment. The horizontal scale, rainfall rate, convective momentum transport, and transverse circulation are about double the respective value in the control simulation. The positive sign of the convective momentum transport contrasts with the negative sign for an eastward-propagating TS MCS. The structure of the simulated convective systems resembles shear-parallel organization in the intertropical convergence zone (ITCZ).
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Siqueira, Jose Ricardo, William B. Rossow, Luiz Augusto Toledo Machado i Cindy Pearl. "Structural Characteristics of Convective Systems over South America Related to Cold-Frontal Incursions". Monthly Weather Review 133, nr 5 (1.05.2005): 1045–64. http://dx.doi.org/10.1175/mwr2888.1.
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Abstract International Satellite Cloud Climatology Project (ISCCP DX) and microwave sensor data collected by the Tropical Rainfall Measuring Mission (TRMM) are used to identify and describe structural characteristics of convective systems (CSs) over continental South America (SA) related to cold-frontal incursions in a 3-yr period. An austral wet-season climatology for CS events of the three most important types of front–tropical convection interaction is built by applying latitude–time diagrams and a cloud-tracking method to DX data. Type 1 is characterized by the penetration of a cold front over subtropical SA that interacts with convection and moves with it into lower tropical latitudes. Type 2 refers to Amazon convection and its enhancement in a quasi-stationary northwest–southeast-oriented band extending from the Amazon to subtropical SA along with the passage of a cold front in the subtropics and characterizes the synoptic formation of the South Atlantic convergence zone. A quasi-stationary cold front over subtropical SA that has only weak interaction with tropical convection corresponds to type 3. Results show that the three types of front–tropical convection interaction strongly modulate deep convection over SA, producing mesoscale CSs with significant fractions of deep convective clouds and rain at their mature phase. Type 2 CSs (type 1 CSs) are constituted of larger deep convective cloud fractions with weaker (stronger) vertical development compared to type 1 CSs (type 3 CSs) in the Tropics (subtropics), resulting in larger rain fractions and less (more) presence of convective rain. Type 1 CSs have larger fractions of deep convective clouds and rain but with weaker vertical development in the subtropics than in the Tropics, showing that cold fronts organize convection more in area in the subtropics, but more in vertical extent in the Tropics. Life cycle variations of CS cloud and rain properties show tropical CSs with a more intense initial development and similar structural differences between the CS types and those found at their mature phase.
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Varble, Adam C., Stephen W. Nesbitt, Paola Salio, Joseph C. Hardin, Nitin Bharadwaj, Paloma Borque, Paul J. DeMott i in. "Utilizing a Storm-Generating Hotspot to Study Convective Cloud Transitions: The CACTI Experiment". Bulletin of the American Meteorological Society 102, nr 8 (sierpień 2021): E1597—E1620. http://dx.doi.org/10.1175/bams-d-20-0030.1.
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AbstractThe Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to improve understanding of orographic cloud life cycles in relation to surrounding atmospheric thermodynamic, flow, and aerosol conditions. The deployment to the Sierras de Córdoba range in north-central Argentina was chosen because of very frequent cumulus congestus, deep convection initiation, and mesoscale convective organization uniquely observable from a fixed site. The C-band Scanning Atmospheric Radiation Measurement (ARM) Precipitation Radar was deployed for the first time with over 50 ARM Mobile Facility atmospheric state, surface, aerosol, radiation, cloud, and precipitation instruments between October 2018 and April 2019. An intensive observing period (IOP) coincident with the RELAMPAGO field campaign was held between 1 November and 15 December during which 22 flights were performed by the ARM Gulfstream-1 aircraft. A multitude of atmospheric processes and cloud conditions were observed over the 7-month campaign, including numerous orographic cumulus and stratocumulus events; new particle formation and growth producing high aerosol concentrations; drizzle formation in fog and shallow liquid clouds; very low aerosol conditions following wet deposition in heavy rainfall; initiation of ice in congestus clouds across a range of temperatures; extreme deep convection reaching 21-km altitudes; and organization of intense, hail-containing supercells and mesoscale convective systems. These comprehensive datasets include many of the first ever collected in this region and provide new opportunities to study orographic cloud evolution and interactions with meteorological conditions, aerosols, surface conditions, and radiation in mountainous terrain.
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Yuan, Jian, Robert A. Houze i Andrew J. Heymsfield. "Vertical Structures of Anvil Clouds of Tropical Mesoscale Convective Systems Observed by CloudSat". Journal of the Atmospheric Sciences 68, nr 8 (1.08.2011): 1653–74. http://dx.doi.org/10.1175/2011jas3687.1.
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Abstract A global study of the vertical structures of the clouds of tropical mesoscale convective systems (MCSs) has been carried out with data from the CloudSat Cloud Profiling Radar. Tropical MCSs are found to be dominated by cloud-top heights greater than 10 km. Secondary cloud layers sometimes occur in MCSs, but outside their primary raining cores. The secondary layers have tops at 6–8 and 1–3 km. High-topped clouds extend outward from raining cores of MCSs to form anvil clouds. Closest to the raining cores, the anvils tend to have broader distributions of reflectivity at all levels, with the modal values at higher reflectivity in their lower levels. Portions of anvil clouds far away from the raining core are thin and have narrow frequency distributions of reflectivity at all levels with overall weaker values. This difference likely reflects ice particle fallout and therefore cloud age. Reflectivity histograms of MCS anvil clouds vary little across the tropics, except that (i) in continental MCS anvils, broader distributions of reflectivity occur at the uppermost levels in the portions closest to active raining areas; (ii) the frequency of occurrence of stronger reflectivity in the upper part of anvils decreases faster with increasing distance in continental MCSs; and (iii) narrower-peaked ridges are prominent in reflectivity histograms of thick anvil clouds close to the raining areas of connected MCSs (superclusters). These global results are consistent with observations at ground sites and aircraft data. They present a comprehensive test dataset for models aiming to simulate process-based upper-level cloud structure around the tropics.
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Rickenbach, Thomas, Paul Kucera, Megan Gentry, Larry Carey, Andrew Lare, Ruei-Fong Lin, Belay Demoz i David O’C Starr. "The Relationship between Anvil Clouds and Convective Cells: A Case Study in South Florida during CRYSTAL-FACE". Monthly Weather Review 136, nr 10 (październik 2008): 3917–32. http://dx.doi.org/10.1175/2008mwr2441.1.
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One of the important goals of NASA’s Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE) was to further the understanding of the evolution of tropical anvil clouds generated by deep convective systems. An important step toward understanding the radiative properties of convectively generated anvil clouds is to study their life cycle. Observations from ground-based radar, geostationary satellite radiometers, aircraft, and radiosondes during CRYSTAL-FACE provided a comprehensive look at the generation of anvil clouds by convective systems over South Florida during July 2002. This study focused on the relationship between convective rainfall and the evolution of the anvil cloud shield associated with convective systems over South Florida on 23 July 2002, during the CRYSTAL-FACE experiment. Anvil clouds emanating from convective cells grew downwind (to the southwest), reaching their maximum area at all temperature thresholds 1–2 h after the active convective cells collapsed. Radar reflectivity data revealed that precipitation-sized anvil particles extended downwind with the cloud tops. The time lag between maximum rainfall and maximum anvil cloud area increased with system size and rainfall. Observations from airborne radar and analysis of in situ cloud particle size distribution measurements in the anvil region suggested that gravitational size sorting of cloud particles dispersed downshear was a likely mechanism in the evolution of the anvil region. Linear regression analysis suggested a positive trend between this time lag and maximum convective rainfall for this case, as well as between the time lag and maximum system cloud cover. The injection of condensate into the anvil region by large areas of intense cells and dispersal in the upper-level winds was a likely explanation to cause the anvil cloud-top area to grow for 1–2 h after the surface convective rainfall began to weaken. In future work these relationships should be evaluated in differing regimes of shear, stability, or precipitation efficiency, such as over the tropical oceans, in order to generalize the results. The results of this study implied that for these cloud systems, the maximum in latent heating (proportional to rainfall) may precede the peak radiative forcing (related to anvil cloud height and area) by a lead time that was proportional to system size and strength. Mesoscale modeling simulations of convective systems on this day are under way to examine anvil evolution and growth mechanisms.
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Bouniol, Dominique, Rémy Roca, Thomas Fiolleau i D. Emmanuel Poan. "Macrophysical, Microphysical, and Radiative Properties of Tropical Mesoscale Convective Systems over Their Life Cycle". Journal of Climate 29, nr 9 (22.04.2016): 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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Rutledge, Steven A., Chungu Lu i Donald R. MacGorman. "Positive Cloud-to-Ground Lightning in Mesoscale Convective Systems". Journal of the Atmospheric Sciences 47, nr 17 (wrzesień 1990): 2085–100. http://dx.doi.org/10.1175/1520-0469(1990)047<2085:pctgli>2.0.co;2.
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Parker, Matthew D., Steven A. Rutledge i Richard H. Johnson. "Cloud-to-Ground Lightning in Linear Mesoscale Convective Systems". Monthly Weather Review 129, nr 5 (maj 2001): 1232–42. http://dx.doi.org/10.1175/1520-0493(2001)129<1232:ctglil>2.0.co;2.
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Reinares Martínez, Irene, i Jean-Pierre Chaboureau. "Precipitation and Mesoscale Convective Systems: Explicit versus Parameterized Convection over Northern Africa". Monthly Weather Review 146, nr 3 (1.03.2018): 797–812. http://dx.doi.org/10.1175/mwr-d-17-0202.1.
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Abstract Precipitating systems are analyzed during a dust event from 9 to 14 June 2006 over northern Africa. A common analysis is applied to satellite observations and two Meso-NH simulations: one convection permitting (grid spacing x = 2.5 km) and the other with parameterized convection (x = 20 km). The precipitating systems are identified as cloud objects and classified as deep convective clouds (DCCs) or other clouds according to their infrared signature. Large DCCs [hereafter named mesoscale convective systems (MCSs)] are tracked, characterized in terms of precipitation and thermodynamic profiles, and analyzed in southern West Africa (SWA), central Africa, and Ethiopia. Precipitation is mostly observed along 0°–15°N, with 71% of the total precipitation produced by all DCCs and 55% by long-lived MCSs. It shows a marked diurnal cycle with a peak in the evening, mainly due to long-lived MCSs, which are characterized by an increase in size, zonal speed, and duration from east to west, with the largest, fastest, and longest-lived ones found over SWA. This is due to an enhanced African easterly jet (AEJ) and monsoon flow leading to stronger shear and greater conditional instability. The simulation with parameterized convection fails to distribute precipitation correctly. The convection-permitting simulation captures most of the observed precipitation features, but lacks the increase in organization of the long-lived MCSs over SWA. Excess moisture in a too zonal AEJ flow suggests that the long-lived MCSs in SWA are poorly located with respect to African easterly waves. The convection-permitting model improves the representation of precipitation but without fully resolving the long-lived MCSs.
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Rossow, William B., Ademe Mekonnen, Cindy Pearl i Weber Goncalves. "Tropical Precipitation Extremes". Journal of Climate 26, nr 4 (15.02.2013): 1457–66. http://dx.doi.org/10.1175/jcli-d-11-00725.1.
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Abstract Classifying tropical deep convective systems by the mesoscale distribution of their cloud properties and sorting matching precipitation measurements over an 11-yr period reveals that the whole distribution of instantaneous precipitation intensity and daily average accumulation rate is composed of (at least) two separate distributions representing distinctly different types of deep convection associated with different meteorological conditions (the distributions of non-deep-convective situations are also shown for completeness). The two types of deep convection produce very different precipitation intensities and occur with very different frequencies of occurrence. Several previous studies have shown that the interaction of the large-scale tropical circulation with deep convection causes switching between these two types, leading to a substantial increase of precipitation. In particular, the extreme portion of the tropical precipitation intensity distribution, above 2 mm h−1, is produced by 40% of the larger, longer-lived mesoscale-organized type of convection with only about 10% of the ordinary convection occurrences producing such intensities. When average precipitation accumulation rates are considered, essentially all of the values above 2 mm h−1 are produced by the mesoscale systems. Yet today’s atmospheric models do not represent mesoscale-organized deep convective systems that are generally larger than current-day circulation model grid cell sizes but smaller than the resolved dynamical scales and last longer than the typical physics time steps. Thus, model-based arguments for how the extreme part of the tropical precipitation distribution might change in a warming climate are suspect.
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Zhang, Sidou, Shiyin Liu i Tengfei Zhang. "Analysis on the Evolution and Microphysical Characteristics of Two Consecutive Hailstorms in Spring in Yunnan, China". Atmosphere 12, nr 1 (2.01.2021): 63. http://dx.doi.org/10.3390/atmos12010063.
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By using products of the cloud model, National Centers for Environmental Prediction (NCEP) Final Operational Global Analysis (FNL) reanalysis data, and Doppler weather radar data, the mesoscale characteristics, microphysical structure, and mechanism of two hail cloud systems which occurred successively within 24 h in southeastern Yunnan have been analyzed. The results show that under the influence of two southwest jets in front of the south branch trough (SBT) and the periphery of the western Pacific subtropical high (WPSH), the northeast-southwest banded echoes affect the southeastern Yunnan of China twice. Meanwhile, the local mesoscale radial wind convergence and uneven wind speed lead to the intense development of convective echoes and the occurrence of hail. The simulated convective cloud bands are similar to the observation. The high-level mesoscale convergence line leads to the development of convective cloud bands. The low-level wind direction or wind speed convergence and the high-level wind speed divergence form a deep tilted updraft, with the maximum velocity of 15 m·s−1 at the −40~−10 °C layer, resulting in the intense development of local convective clouds. The hail embryos form through the conversion or collision growth of cloud water and snowflakes and have little to do with rain and ice crystals. Abundant cloud water, especially the accumulation region of high supercooled water (cloud water) near the 0 °C layer, is the key to the formation of hail embryos, in which qc is up to 1.92 g·kg−1 at the −4~−2 °C layer. The hail embryos mainly grow by collision-coalescence (collision-freezing) with cloud water (supercooled cloud drops) and snow crystal riming.
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NAGORSKII, P. M., D. F. ZHUKOV, M. S. KARTAVYKH, M. V. OGLEZNEVA, K. N. PUSTOVALOV i S. V. SMIRNOV. "PROPERTIES AND STRUCTURE OF MESOSCALE CONVECTIVE SYSTEMS OVER WESTERN SIBERIA ACCORDING TO REMOTE OBSERVATIONS". Meteorologiya i Gidrologiya, nr 12 (grudzień 2022): 45–55. http://dx.doi.org/10.52002/0130-2906-2022-12-45-55.
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Many natural hazards are associated with deep convective clouds. Among them, mesoscale convective systems characterized by a large size and a long duration are the most dangerous. The estimates of their area, cloud top height, moisture content, duration, and intensity of related thunderstorm activity for Western Siberia were obtained using the data of radio and optical (passive and active) satellite sounding (for the summer months in 2010-2019) and World Wide Lightning Location Network (WWLLN, 2016-2020).
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Moncrieff, Mitchell W., i Todd P. Lane. "Long-Lived Mesoscale Systems in a Low–Convective Inhibition Environment. Part II: Downshear Propagation". Journal of the Atmospheric Sciences 72, nr 11 (1.11.2015): 4319–36. http://dx.doi.org/10.1175/jas-d-15-0074.1.
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Abstract Part II of this study of long-lived convective systems in a tropical environment focuses on forward-tilted, downshear-propagating systems that emerge spontaneously from idealized numerical simulations. These systems differ in important ways from the standard mesoscale convective system that is characterized by a rearward-tilted circulation with a trailing stratiform region, an overturning updraft, and a mesoscale downdraft. In contrast to this standard mesoscale system, the downshear-propagating system considered here does not feature a mesoscale downdraft and, although there is a cold pool it is of secondary importance to the propagation and maintenance of the system. The mesoscale downdraft is replaced by hydraulic-jump-like ascent beneath an elevated, forward-tilted overturning updraft with negligible convective available potential energy. Therefore, the mesoscale circulation is sustained almost entirely by the work done by the horizontal pressure gradient and the kinetic energy available from environmental shear. This category of organization is examined by cloud-system-resolving simulations and approximated by a nonlinear archetypal model of the quasi-steady Lagrangian-mean mesoscale circulation.
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Laing, Arlene G., Richard E. Carbone i Vincenzo Levizzani. "Cycles and Propagation of Deep Convection over Equatorial Africa". Monthly Weather Review 139, nr 9 (wrzesień 2011): 2832–53. http://dx.doi.org/10.1175/2011mwr3500.1.
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Long-term statistics of organized convection are vital to improved understanding of the hydrologic cycle at various scales. Satellite observations are used to understand the timing, duration, and frequency of deep convection in equatorial Africa, a region with some of the most intense thunderstorms. Yet little has been published about the propagation characteristics of mesoscale convection in that region. Diurnal, subseasonal, and seasonal cycles of cold cloud (proxy for convective precipitation) are examined on a continental scale. Organized deep convection consists of coherent structures that are characteristic of systems propagating under a broad range of atmospheric conditions. Convection is triggered by heating of elevated terrain, sea/land breezes, and lake breezes. Coherent episodes of convection result from regeneration of convection through multiple diurnal cycles while propagating westward. They have an average 17.6-h duration and 673-km span; most have zonal phase speeds of 8–16 m s−1. Propagating convection occurs in the presence of moderate low-level shear that is associated with the southwesterly monsoonal flow and midlevel easterly jets. Convection is also modulated by eastward-moving equatorially trapped Kelvin waves, which have phase speeds of 12–22 m s−1 over equatorial Africa. Westward propagation of mesoscale convection is interrupted by the dry phase of convectively coupled Kelvin waves. During the wet phase, daily initiation and westward propagation continues within the Kelvin wave and the cold cloud shields are larger. Mesoscale convection is more widespread during the active phase of the Madden–Julian oscillation (MJO) but with limited westward propagation. The study highlights multiscale interaction as a major source of variability in convective precipitation during the critical rainy seasons in equatorial Africa.
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Zeng, Xiping, Wei-Kuo Tao, Scott W. Powell, Robert A. Houze, Paul Ciesielski, Nick Guy, Harold Pierce i Toshihisa Matsui. "A Comparison of the Water Budgets between Clouds from AMMA and TWP-ICE". Journal of the Atmospheric Sciences 70, nr 2 (1.02.2013): 487–503. http://dx.doi.org/10.1175/jas-d-12-050.1.
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Abstract Two field campaigns, the African Monsoon Multidisciplinary Analysis (AMMA) and the Tropical Warm Pool–International Cloud Experiment (TWP-ICE), took place in 2006 near Niamey, Niger, and Darwin, Northern Territory, Australia, providing extensive observations of mesoscale convective systems (MCSs) near a desert and a tropical coast, respectively. Under the constraint of their observations, three-dimensional cloud-resolving model simulations are carried out and presented in this paper to replicate the basic characteristics of the observed MCSs. All of the modeled MCSs exhibit a distinct structure having deep convective clouds accompanied by stratiform and anvil clouds. In contrast to the approximately 100-km-scale MCSs observed in TWP-ICE, the MCSs in AMMA have been successfully simulated with a scale of about 400 km. These modeled AMMA and TWP-ICE MCSs offer an opportunity to understand the structure and mechanism of MCSs. Comparing the water budgets between AMMA and TWP-ICE MCSs suggests that TWP-ICE convective clouds have stronger ascent while the mesoscale ascent outside convective clouds in AMMA is stronger. A case comparison, with the aid of sensitivity experiments, also suggests that vertical wind shear and ice crystal (or dust aerosol) concentration can significantly impact stratiform and anvil clouds (e.g., their areas) in MCSs. In addition, the obtained water budgets quantitatively describe the transport of water between convective, stratiform, and anvil regions as well as water sources/sinks from microphysical processes, providing information that can be used to help determine parameters in the convective and cloud parameterizations in general circulation models (GCMs).
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Prasetyo, Suwignyo. "Synoptic and Mesoscale Analysis of Extreme Rainfall Event in Cilacap Meteorological Station, Indonesia on December 7, 2018". Jurnal Ilmu dan Inovasi Fisika 5, nr 2 (9.08.2021): 121–31. http://dx.doi.org/10.24198/jiif.v5i2.31258.
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The highest rainfall for the last five years (2016-2020) was recorded at 199.5 mm in twenty-four hours at the Cilacap Meteorological Station. This study examines the dynamics of the atmosphere with a focus on the synoptic scale and the meso scale. This is done because high rainfall with a long duration is usually caused by a wider scale atmospheric circulation than just local convection scale. The rush of cold air masses from the Asian highlands that propagates across the equator is the main cause on the synoptic scale. In addition, the air flow from the south meets the air mass flow from the north right on the island of Java. On the meso scale, numerical simulations have not been able to properly estimate rainfall with values that tend to be underestimated. However, the value of convective available potential energy is high enough to support the growth of convective clouds. Based on himawari-8 satellite imagery, it is clearly observed that the clouds formed due to atmospheric dynamics are meso-scale convective cloud systems with a life span of more than six hours. The cloud growth is quite massive, which is indicated by the cloud top temperature value being lower than -80C in the mature phase. Thus, the resulting rainfall is quite heavy, causing flooding in parts of Cilacap
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Ziv, Baruch, Yoav Yair, Karin Presman i Martin Füllekrug. "Assessment of the Aviation Weather Center Global Forecasts of Mesoscale Convective Systems*". Journal of Applied Meteorology 43, nr 5 (1.05.2004): 720–26. http://dx.doi.org/10.1175/2097.1.
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Abstract This paper examines the precision of location and top height of mesoscale convective systems, as forecast by the Aviation Weather Center (AWC). The examination was motivated by the Mediterranean Israeli Dust Experiment (MEIDEX) on the space shuttle Columbia, aimed to image transient luminous events (TLEs), such as sprites, jets, and elves, from orbit. Mesoscale convective systems offer a high probability for the occurrence of TLEs above active thunderstorms. Because the operational methodology was planned around a 24-h cycle, there was a need for a global forecast of areas with a high probability of massive thunderstorms that are prone to exhibit TLE activity. The forecast was based on the high-level significant weather (SIGWX) maps, commonly used for civil aviation, provided by the AWC on the Internet. To estimate the operational skill of this forecast for successfully detecting clouds with a high probability for producing TLEs, predictions for selected dates were compared with satellite observations. The locations of 66 mesoscale cloud systems on Significant Weather Maps, produced for eight different dates in August 2001, were compared with satellite global IR images for these dates. Operational skill was determined as the percentage of observed cloud systems found within a 5° range in the regions that appeared on the forecast maps as having the potential to contain thunderclouds and was found to be 92%. No consistent error was found in location. The predicted size of the convective system was typically larger than the observed size. Cloud-top heights of 53 systems were examined on four dates in October–November 2001, using IR radiances converted to brightness temperatures. For each convective system, the coldest cloud-top temperature was converted to height, using the NCEP–NCAR reanalysis data for the respective location and time. The standard error in the forecast heights was 2516 m. Because the purpose was to get true alerts of potential TLE occurrences, operational forecast skill was defined as the percentage of forecasts that were accurate within 1000 m or higher than observed. The 1000-m tolerance was allowed because of inevitable uncertainties underlying this method of analysis. Operational skill was found to be only 43%. During the “STS-107” mission flown in January 2003, the forecasted areas of main convective centers were transmitted daily to the crew and helped them in pointing the cameras and targeting thunderstorms. This ensured the success of the MEIDEX sprite observations that recorded numerous events in many different geographical locations.
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Tulich, Stefan N., i Brian E. Mapes. "Multiscale Convective Wave Disturbances in the Tropics: Insights from a Two-Dimensional Cloud-Resolving Model". Journal of the Atmospheric Sciences 65, nr 1 (1.01.2008): 140–55. http://dx.doi.org/10.1175/2007jas2353.1.
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Abstract Multiscale convective wave disturbances with structures broadly resembling observed tropical waves are found to emerge spontaneously in a nonrotating, two-dimensional cloud model forced by uniform cooling. To articulate the dynamics of these waves, model outputs are objectively analyzed in a discrete truncated space consisting of three cloud types (shallow convective, deep convective, and stratiform) and three dynamical vertical wavelength bands. Model experiments confirm that diabatic processes in deep convective and stratiform regions are essential to the formation of multiscale convective wave patterns. Specifically, upper-level heating (together with low-level cooling) serves to preferentially excite discrete horizontally propagating wave packets with roughly a full-wavelength structure in troposphere and “dry” phase speeds cn in the range 16–18 m s−1. These wave packets enhance the triggering of new deep convective cloud systems, via low-level destabilization. The new convection in turn causes additional heating over cooling, through delayed development of high-based deep convective cells with persistent stratiform anvils. This delayed forcing leads to an intensification and then widening of the low-level cold phases of wave packets as they move through convecting regions. Additional widening occurs when slower-moving (∼8 m s−1) “gust front” wave packets excited by cooling just above the boundary layer trigger additional deep convection in the vicinity of earlier convection. Shallow convection, meanwhile, provides positive forcing that reduces convective wave speeds and destroys relatively small-amplitude-sized waves. Experiments with prescribed modal wind damping establish the critical role of short vertical wavelengths in setting the equivalent depth of the waves. However, damping of deep vertical wavelengths prevents the clustering of mesoscale convective wave disturbances into larger-scale envelopes, so these circulations are important as well.
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Tromeur, Eric, i William B. Rossow. "Interaction of Tropical Deep Convection with the Large-Scale Circulation in the MJO". Journal of Climate 23, nr 7 (1.04.2010): 1837–53. http://dx.doi.org/10.1175/2009jcli3240.1.
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Abstract To better understand the interaction between tropical deep convection and the Madden–Julian oscillation (MJO), tropical cloud regimes are defined by cluster analysis of International Satellite Cloud Climatology Project (ISCCP) cloud-top pressure—optical thickness joint distributions from the D1 dataset covering 21.5 yr. An MJO index based solely on upper-level wind anomalies is used to study variations of the tropical cloud regimes. The MJO index shows that MJO events are present almost all the time; instead of the MJO event being associated with “on or off” deep convection, it is associated with weaker or stronger mesoscale organization of deep convection. Atmospheric winds and humidity from NCEP–NCAR reanalysis 1 are used to characterize the large-scale dynamics of the MJO; the results show that the large-scale motions initiate an MJO event by moistening the lower troposphere by horizontal advection. Increasingly strong convection transports moisture into the upper troposphere, suggesting a reinforcement of the convection itself. The change of convection organization shown by the cloud regimes indicates a strong interaction between the large-scale circulation and deep convection. The analysis is extended to the complete atmospheric diabatic heating by precipitation, radiation, and surface fluxes. The wave organizes stronger convective heating of the tropical atmosphere, which results in stronger winds, while there is only a passive response of the surface, directly linked to cloud radiative effects. Overall, the results suggest that an MJO event is an amplification of large-scale wave motions by stronger convective heating, which results from a dynamic reorganization of scattered deep convection into more intense mesoscale systems.
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Martínez, Irene Reinares, i Jean-Pierre Chaboureau. "Precipitation and Mesoscale Convective Systems: Radiative Impact of Dust over Northern Africa". Monthly Weather Review 146, nr 9 (30.08.2018): 3011–29. http://dx.doi.org/10.1175/mwr-d-18-0103.1.
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Abstract The radiative effect of dust on precipitation and mesoscale convective systems (MCSs) is examined during a case of dust emission and transport from 9 to 14 June 2006 over northern Africa. The same method to identify and track different cloud types is applied to satellite observations and two convection-permitting simulations (with grid mesh of 2.5 km), with and without the radiative effect of dust, performed with the MesoNH model. The MCSs produce most of the observed total precipitation (66%), and the long-lived systems (lasting 6 h or more) are responsible for 55% of the total. Both simulations reproduce the observed distribution of precipitation between the cloud categories but differ due to the radiative effects of dust. The overall impacts of dust are a warming of the midtroposphere; a cooling of the near surface, primarily in the western parts of northern Africa; and a decrease in precipitation due to a too-low number of long-lived MCSs. The drop in their number is due to the stabilization of the lower atmosphere, which inhibits the triggering of convection. The long-lived MCSs are a little longer lived, faster, and more efficient in rainfall production when accounting for the dust–radiation interaction. This higher degree of organization is due to the larger convective available potential energy and an intensified African easterly jet. The latter is, in turn, a response to the variation in the meridional gradient of the temperature induced by the dust.
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Blamey, R. C., i C. J. C. Reason. "Mesoscale Convective Complexes over Southern Africa". Journal of Climate 25, nr 2 (15.01.2012): 753–66. http://dx.doi.org/10.1175/jcli-d-10-05013.1.
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Abstract The maximum spatial correlation technique (MASCOTTE) is an objective and automated method developed to simultaneously determine both the structural properties and evolution (tracking) of cloud shields of convective systems. Originally designed to monitor systems over the Amazon region, this method has now been adapted for subtropical southern Africa. In this paper, a detailed climatology of 70 mesoscale convective complexes (MCCs) that occurred during the austral summer months over southern Africa during the 1998–2006 period are presented. Most MCCs are clustered along the eastern regions of southern Africa, adjacent to the warm waters of the Mozambique Channel and Agulhas Current. A few infrequent systems are found to be developing in Namibia and Botswana. The systems are found to predominantly occur during the months of November–February, with maximum activity occurring in November and December. The transition from a more midlatitude-dominated circulation to a tropical circulation over the region during the late summer leads to an uncharacteristic equatorward migration of the MCC distribution then. The analysis also suggests that there is variability in MCC frequency on monthly and seasonal time scales. Although fewer in number (about nine per season) compared to MCC populations in other regions, the systems do tend to follow the nocturnal life cycle as documented elsewhere.
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Pritchard, Michael S., Mitchell W. Moncrieff i Richard C. J. Somerville. "Orogenic Propagating Precipitation Systems over the United States in a Global Climate Model with Embedded Explicit Convection". Journal of the Atmospheric Sciences 68, nr 8 (1.08.2011): 1821–40. http://dx.doi.org/10.1175/2011jas3699.1.
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Abstract In the lee of major mountain chains worldwide, diurnal physics of organized propagating convection project onto seasonal and climate time scales of the hydrologic cycle, but this phenomenon is not represented in conventional global climate models (GCMs). Analysis of an experimental version of the superparameterized (SP) Community Atmosphere Model (CAM) demonstrates that propagating orogenic nocturnal convection in the central U.S. warm season is, however, representable in GCMs that use the embedded explicit convection model approach [i.e., multiscale modeling frameworks (MMFs)]. SP-CAM admits propagating organized convective systems in the lee of the Rockies during synoptic conditions similar to those that generate mesoscale convective systems in nature. The simulated convective systems exhibit spatial scales, phase speeds, and propagation speeds comparable to radar observations, and the genesis mechanism in the model agrees qualitatively with established conceptual models. Convective heating and condensate structures are examined on both resolved scales in SP-CAM, and coherently propagating cloud “metastructures” are shown to transcend individual cloud-resolving model arrays. In reconciling how this new mode of diurnal convective variability is admitted in SP-CAM despite the severe idealizations in the cloud-resolving model configuration, an updated discussion is presented of what physics may transcend the re-engineered scale interface in MMFs. The authors suggest that the improved diurnal propagation physics in SP-CAM are mediated by large-scale first-baroclinic gravity wave interactions with a prognostic organization life cycle, emphasizing the physical importance of preserving “memory” at the inner resolved scale.
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Yuan, Jian, i Robert A. Houze. "Deep Convective Systems Observed by A-Train in the Tropical Indo-Pacific Region Affected by the MJO". Journal of the Atmospheric Sciences 70, nr 2 (1.02.2013): 465–86. http://dx.doi.org/10.1175/jas-d-12-057.1.
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Abstract In the Indo-Pacific region, mesoscale convective systems (MCSs) occur in a pattern consistent with the eastward propagation of the large-scale convective envelope of the Madden–Julian oscillation (MJO). MCSs are major contributors to the total precipitation. Over the open ocean they tend to be merged or connected systems, while over the Maritime Continent area they tend to be separated or discrete. Over all regions affected by the MJO, connected systems increase in frequency during the active phase of the MJO. Characteristics of each type of MCS (separated or connected) do not vary much over MJO-affected regions. However, separated and connected MCSs differ in structure from each other. Connected MCSs have a larger size and produce less but colder-topped anvil cloud. For both connected and separated MCSs, larger systems tend to have colder cloud tops and less warmer-topped anvil cloud. The maximum height of MCS precipitating cores varies only slightly, and the variation is related to sea surface temperature. Enhanced large-scale convection, greater frequency of occurrence of connected MCSs, and increased midtroposphere moisture coincide, regardless of the region, season, or large-scale conditions (such as the concurrent phase of the MJO), suggesting that the coexistence of these phenomena is likely the nature of deep convection in this region. The increase of midtroposphere moisture observed in all convective regimes during large-scale convectively active phases suggests that the source of midtroposphere moisture is not local or instantaneous and that the accumulation of midtroposphere moisture over MJO-affected regions needs to be better understood.
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Coniglio, Michael C., Harold E. Brooks, Steven J. Weiss i Stephen F. Corfidi. "Forecasting the Maintenance of Quasi-Linear Mesoscale Convective Systems". Weather and Forecasting 22, nr 3 (1.06.2007): 556–70. http://dx.doi.org/10.1175/waf1006.1.
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Abstract The problem of forecasting the maintenance of mesoscale convective systems (MCSs) is investigated through an examination of observed proximity soundings. Furthermore, environmental variables that are statistically different between mature and weakening MCSs are input into a logistic regression procedure to develop probabilistic guidance on MCS maintenance, focusing on warm-season quasi-linear systems that persist for several hours. Between the mature and weakening MCSs, shear vector magnitudes over very deep layers are the best discriminators among hundreds of kinematic and thermodynamic variables. An analysis of the shear profiles reveals that the shear component perpendicular to MCS motion (usually parallel to the leading line) accounts for much of this difference in low levels and the shear component parallel to MCS motion accounts for much of this difference in mid- to upper levels. The lapse rates over a significant portion of the convective cloud layer, the convective available potential energy, and the deep-layer mean wind speed are also very good discriminators and collectively provide a high level of discrimination between the mature and dissipation soundings as revealed by linear discriminant analysis. Probabilistic equations developed from these variables used with short-term numerical model output show utility in forecasting the transition of an MCS with a solid line of 50+ dBZ echoes to a more disorganized system with unsteady changes in structure and propagation. This study shows that empirical forecast tools based on environmental relationships still have the potential to provide forecasters with improved information on the qualitative characteristics of MCS structure and longevity. This is especially important since the current and near-term value added by explicit numerical forecasts of convection is still uncertain.
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Feng, Zhe, Joseph Hardin, Hannah C. Barnes, Jianfeng Li, L. Ruby Leung, Adam Varble i Zhixiao Zhang. "PyFLEXTRKR: a flexible feature tracking Python software for convective cloud analysis". Geoscientific Model Development 16, nr 10 (23.05.2023): 2753–76. http://dx.doi.org/10.5194/gmd-16-2753-2023.
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Abstract. This paper describes the new open-source framework PyFLEXTRKR (Python FLEXible object TRacKeR), a flexible atmospheric feature tracking software package with specific capabilities to track convective clouds from a variety of observations and model simulations. This software can track any atmospheric 2D objects and handle merging and splitting explicitly. The package has a collection of multi-object identification algorithms, scalable parallelization options, and has been optimized for large datasets including global high-resolution data. We demonstrate applications of PyFLEXTRKR on tracking individual deep convective cells and mesoscale convective systems from observations and model simulations ranging from large-eddy resolving (∼100s m) to mesoscale (∼10s km) resolutions. Visualization, post-processing, and statistical analysis tools are included in the package. New Lagrangian analyses of convective clouds produced by PyFLEXTRKR applicable to a wide range of datasets and scales facilitate advanced model evaluation and development efforts as well as scientific discovery.
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Zovko-Rajak, Dragana, i Todd P. Lane. "The Generation of Near-Cloud Turbulence in Idealized Simulations". Journal of the Atmospheric Sciences 71, nr 7 (20.06.2014): 2430–51. http://dx.doi.org/10.1175/jas-d-13-0346.1.
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Abstract This study explores the generation of turbulence in the upper outflow regions of simulated idealized mesoscale convective systems. The simulated storms are shown to generate parameterized turbulence that occurs significant distances (>100 km) from the main convective regions, in both the clear air surrounding the convection and low simulated reflectivity regions with cloud ice but negligible amounts of graupel and snow. The source of the turbulence is related to Kelvin–Helmholtz instabilities that occur in the shear zones above and below the storm-induced upper-level outflow jet that is centered near the tropopause; the model produces resolved-scale billows within regions of low gradient Richardson number. Short-scale gravity waves are also coincident with the regions of turbulence, become trapped within the jet core, and appear to be generated by the shear instability. Additional experiments with different initial upper-level wind shear show similar mechanisms to those simulations with no initial upper-level shear. These results help elucidate the dynamics of turbulence generation near convection, which has important implications for the aviation industry and the fundamental understanding of how convective clouds interact with their environment.
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Chen, Shu-Hua, i Yuh-Lang Lin. "Effects of Moist Froude Number and CAPE on a Conditionally Unstable Flow over a Mesoscale Mountain Ridge". Journal of the Atmospheric Sciences 62, nr 2 (1.02.2005): 331–50. http://dx.doi.org/10.1175/jas-3380.1.
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Abstract In this study, idealized simulations are performed for a conditionally unstable flow over a two-dimensional mountain ridge in order to investigate the propagation and types of cloud precipitation systems controlled by the unsaturated moist Froude number (Fw) and the convective available potential energy (CAPE). A two-dimensional moist flow regime diagram, based on Fw and CAPE, is proposed for a conditionally unstable flow passing over a two-dimensional mesoscale mountain ridge. The characteristics of these flow regimes are 1) regime I: flow with an upstream-propagating convective system and an early, slowly moving convective system over the mountain; 2) regime II: flow with a long-lasting orographic convective system over the mountain peak, upslope, or lee slope; 3) regime III: flow with an orographic convective or mixed convective and stratiform precipitation system over the mountain and a downstream-propagating convective system; and 4) regime IV: flow with an orographic stratiform precipitation system over the mountain and possibly a downstream-propagating cloud system. Note that the fourth regime was not included in the flow regimes proposed by Chu and Lin and Chen and Lin. The propagation of the convective systems is explained by the orographic blocking and density current forcing associated with the cold-air outflow produced by evaporative cooling acting against the basic flow, which then determines the propagation and cloud types of the simulated precipitation systems.
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Holder, Christopher T., Sandra E. Yuter, Adam H. Sobel i Anantha R. Aiyyer. "The Mesoscale Characteristics of Tropical Oceanic Precipitation during Kelvin and Mixed Rossby–Gravity Wave Events". Monthly Weather Review 136, nr 9 (1.09.2008): 3446–64. http://dx.doi.org/10.1175/2008mwr2350.1.
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Abstract Precipitation structures within Kelvin and mixed Rossby–gravity (MRG) wave troughs near Kwajalein Atoll during the 1999–2003 rainy seasons are analyzed using three-dimensional ground-based radar data and upper-air sounding data. Consistent with previous work, wave troughs are preferred locations for precipitation and typically yield 1.3 times more rain area compared to the overall rainy season climatology. Although the contiguous areas of cold cloudiness associated with tropical wave troughs are large and long lived, the underlying precipitation structure is most frequently small, isolated convection from mixed-phase clouds. This mismatch in instantaneous cold cloudiness area versus radar-observed precipitation area indicates differences in the rate and nature of evolution between the mesoscale anvil cloud and the underlying precipitating portion of the cloud. Mesoscale convective systems (MCSs) were identified during portions of 32 of the 39 wave trough events examined. Convective cells are frequently embedded within stratiform regions. Reflectivity holes or pores in contiguous radar echo have been frequently observed in other regions but are quantified for the first time in this study. Based on characteristics such as total size of precipitating area and occurrence of convective lines, MCSs within Kelvin troughs are slightly more organized than those occurring within MRG troughs. Similar to the west Pacific warm pool region, there is a well-defined separation between observed and unobserved stratiform area fraction and convective precipitation area, each as a function of total precipitation area. At precipitation area sizes near 40% of the radar domain, the maximum observed convective area changes from increasing to decreasing with increasing precipitation area. The maximum observed convective precipitation area occupied ∼20% of the radar domain. These characteristics suggest that the atmosphere in the west Pacific can sustain a limited area of updrafts capable of supporting precipitation growth by collision/coalescence and riming.
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Shikhov, A. N., A. V. Chernokulsky, A. A. Sprygin i I. O. Azhigov. "Identification of mesoscale convective cloud systems with tornadoes using satellite data". Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa 16, nr 1 (2019): 223–36. http://dx.doi.org/10.21046/2070-7401-2019-16-1-223-236.
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MacGorman, Donald R., i Carolyn D. Morgenstern. "Some characteristics of cloud-to-ground lightning in mesoscale convective systems". Journal of Geophysical Research: Atmospheres 103, nr D12 (1.06.1998): 14011–23. http://dx.doi.org/10.1029/97jd03221.
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Bell, Michael M., i Michael T. Montgomery. "Mesoscale Processes during the Genesis of Hurricane Karl (2010)". Journal of the Atmospheric Sciences 76, nr 8 (11.07.2019): 2235–55. http://dx.doi.org/10.1175/jas-d-18-0161.1.
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Abstract Observations from the Pre-Depression Investigation of Cloud Systems in the Tropics (PREDICT), Genesis and Rapid Intensification Processes (GRIP), and Intensity Forecast Experiment (IFEX) field campaigns are analyzed to investigate the mesoscale processes leading to the tropical cyclogenesis of Hurricane Karl (2010). Research aircraft missions provided Doppler radar, in situ flight level, and dropsonde data documenting the structural changes of the predepression disturbance. Following the pre-Karl wave pouch, variational analyses at the meso-β and meso-α scales suggest that the convective cycle in Karl alternately built the low- and midlevel circulations leading to genesis episodically rather than through a sustained lowering of the convective mass flux from increased stabilization. Convective bursts that erupt in the vorticity-rich environment of the recirculating pouch region enhance the low-level meso-β- and meso-α-scale circulation through vortex stretching. As the convection wanes, the resulting stratiform precipitation strengthens the midlevel circulation through convergence associated with ice microphysical processes, protecting the disturbance from the intrusion of dry environmental air. Once the column saturation fraction returns to a critical value, a subsequent convective burst below the midlevel circulation further enhances the low-level circulation, and the convective cycle repeats. The analyses suggest that the onset of deep convection and associated low-level spinup were closely related to the coupling of the vorticity and moisture fields at low and midlevels. Our interpretation of the observational analysis presented in this study reaffirms a primary role of deep convection in the genesis process and provides a hypothesis for the supporting role of stratiform precipitation and the midlevel vortex.
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Kyaw Than Oo. "Review of the History of Mesoscale Convective System Forecasts on Aviation". Journal of Airline Operations and Aviation Management 2, nr 1 (15.08.2023): 68–85. http://dx.doi.org/10.56801/jaoam.v2i1.4.
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Airports are important national resources, and Aviation Weather Services are critical to the aviation industry's success. According to the National Transportation Safety Board's (NTSB) analysis of weather-related circumstances that influence near- surface aircraft operations, wind and turbulence caused 1381 accidents, visibility, ceiling height (hc), and precipitation-related accidents occurred 485 times, and aircraft icing caused 150 accidents between 2003 and 2007. Mesoscale convective systems (MCSs) arise when cumulonimbus clouds merge into a single entity that can span hundreds of miles and continue for hours, posing a higher threat to aviation due to its size and duration. The mesoscale downdraft of a squall-line MCS's stratiform area sometimes merges with the convective downdrafts in the leading line of convection, and these mergers can produce strong effects, with the gust front surging forward and triggering new convection in the form of a “bow echo," according to Doppler radar. Bow echo events are of particular concern to forecasters because they are typically associated with strong, damaging surface winds. Because MCSs are still a major socioeconomic issue, it's critical to construct climate models that incorporate them, whether through cloud-resolving modeling or parameterization. MCS characteristics are influenced by the increasingly contaminated aerosol environment in most parts of the world, and as the Earth warms, MCS patterns will certainly change.
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Stubenrauch, Claudia J., Giacomo Caria, Sofia E. Protopapadaki i Friederike Hemmer. "3D radiative heating of tropical upper tropospheric cloud systems derived from synergistic A-Train observations and machine learning". Atmospheric Chemistry and Physics 21, nr 2 (26.01.2021): 1015–34. http://dx.doi.org/10.5194/acp-21-1015-2021.
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Abstract. Upper tropospheric (UT) cloud systems constructed from Atmospheric Infrared Sounder (AIRS) cloud data provide a horizontal emissivity structure, allowing the convective core to be linked to anvil properties. By using machine learning techniques, we composed a horizontally complete picture of the radiative heating rates deduced from CALIPSO lidar and CloudSat radar measurements, which are only available along narrow nadir tracks. To train the artificial neural networks, we combined the simultaneous AIRS, CALIPSO and CloudSat data with ERA-Interim meteorological reanalysis data in the tropics over a period of 4 years. The resulting non-linear regression models estimate the radiative heating rates as a function of about 40 cloud, atmospheric and surface properties, with a column-integrated mean absolute error (MAE) of 0.8 K d−1 (0.5 K d−1) for cloudy scenes and 0.4 K d−1 (0.3 K d−1) for clear sky in the longwave (shortwave) spectral domain. Developing separate models for (i) high opaque clouds, (ii) cirrus, (iii) mid- and low-level clouds and (iv) clear sky, independently over ocean and over land, leads to a small improvement, when considering the profiles. These models were applied to the whole AIRS cloud dataset, combined with ERA-Interim, to build 3D radiative heating rate fields. Over the deep tropics, UT clouds have a net radiative heating effect of about 0.3 K d−1 throughout the troposphere from 250 hPa downward. This radiative heating enhances the column-integrated latent heating by about 22±3 %. While in warmer regions the net radiative heating profile is nearly completely driven by deep convective cloud systems, it is also influenced by low-level clouds in the cooler regions. The heating rates of the convective systems in both regions also differ: in the warm regions the net radiative heating by the thicker cirrus anvils is vertically more extended, and their surrounding thin cirrus heat the entire troposphere by about 0.5 K d−1. The 15-year time series reveal a slight increase of the vertical heating in the upper and middle troposphere by convective systems with tropical surface temperature warming, which can be linked to deeper systems. In addition, the layer near the tropopause is slightly more heated by increased thin cirrus during periods of surface warming. While the relative coverage of convective systems is relatively stable with surface warming, their depth increases, measured by a decrease of their near-top temperature of -3.4±0.2 K K−1. Finally, the data reveal a connection of the mesoscale convective system (MCS) heating in the upper and middle troposphere and the (low-level) cloud cooling in the lower atmosphere in the cool regions, with a correlation coefficient equal to 0.72, which consolidates the hypothesis of an energetic connection between the convective regions and the subsidence regions.
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Crespo, Juan A., i Derek J. Posselt. "A-Train-Based Case Study of Stratiform–Convective Transition within a Warm Conveyor Belt". Monthly Weather Review 144, nr 6 (6.05.2016): 2069–84. http://dx.doi.org/10.1175/mwr-d-15-0435.1.
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Abstract Clouds are both produced by and interact with the mesoscale and synoptic-scale structure of extratropical cyclones (ETCs) in ways that are still not well understood. Cloud-scale radiative and latent heating modifies the thermal environment, leading to a response in the dynamics that can in turn feed back on cloud distribution and microphysical properties. Key to the structure of ETCs is the warm conveyor belt (WCB); the poleward-ascending airstream that produces the bulk of the clouds and precipitation. This paper examines a long-lived WCB that persisted over the western North Atlantic Ocean in nearly the same location for several days. During this time, the storm was sampled multiple times by NASA’s A-Train satellite constellation, and a clear transition from stratiform to convective clouds was observed. Examination of coincident temperature and water vapor data reveals destabilization of the thermodynamic profile after the cyclone reached maturity. CloudSat radar reflectivity from two sequential overpasses of the warm front depicts a change from stratiform to convective cloud structure, and high-frequency microwave data reveal an increase in the amount of ice hydrometeors. The presence of convection may serve to strengthen the warm frontal trough while slowing the movement of the primary low pressure center. The stratiform–convective transition cannot be detected from passive measurements of cloud-top pressure. The results demonstrate the effectiveness of multivariate satellite observations for examining the outcome of dynamic processes in ETCs, and highlight the need for more rapid temporal profiling in future remote sensing observing systems.
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Xu, Weixin, i Steven A. Rutledge. "Convective Variability Associated with the Boreal Summer Intraseasonal Oscillation in the South China Sea Region". Journal of Climate 31, nr 18 (wrzesień 2018): 7363–83. http://dx.doi.org/10.1175/jcli-d-18-0091.1.
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This study investigates the convective cloud population, precipitation microphysics, and lightning activity associated with the boreal summer intraseasonal oscillation (BSISO) over the South China Sea (SCS) and surrounding landmasses. SCS rainfall shows a marked 30–60-day intraseasonal variability. This variability is less evident over land. The population of mesoscale convective systems (MCSs) and the stratiform rain fraction over the SCS, Philippines, and Indochina increase remarkably after the onset of BSISO. Convection over the SCS during inactive periods exhibits a trimodal population including shallow cumulus, congestus, and deep convection, mirroring the situation over tropical open oceans. The shallow mode is absent over land. Shallow cumulus clouds rapidly transition to congestus clouds over the SCS under active BSISO conditions. Over land, deep convection and lightning lead total rainfall and MCSs by 2–3 BSISO phases, whereas they are somewhat in phase over the SCS. Although convective instability over the SCS is larger during active periods compared to inactive periods, variability in convective intensity and precipitation microphysics is minimal, with active periods showing only higher frequency of moderate ice scattering and 30-dB Z heights extending to −10°C. Over the Philippines and Indochina, inactive phases exhibit substantially stronger ice scattering signatures, robust mixed-phase microphysics, and higher lightning flash rates, possibly due to greater convective instability and a stronger convective diurnal cycle. Total rainfall, convective environments, and convective structures over Borneo are all out of phase with that over the Philippines and Indochina, while southern China shows little BSISO variability on convective intensity and lightning frequency.
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Jackson, Robert C., Scott M. Collis, Valentin Louf, Alain Protat i Leon Majewski. "A 17 year climatology of the macrophysical properties of convection in Darwin". Atmospheric Chemistry and Physics 18, nr 23 (13.12.2018): 17687–704. http://dx.doi.org/10.5194/acp-18-17687-2018.
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Abstract. The validation of convective processes in global climate models (GCMs) could benefit from the use of large datasets that provide long-term climatologies of the spatial statistics of convection. To that regard, echo top heights (ETHs), convective areas, and frequencies of mesoscale convective systems (MCSs) from 17 years of data from a C-band polarization (CPOL) radar are analyzed in varying phases of the Madden–Julian Oscillation (MJO) and northern Australian monsoon in order to provide ample validation statistics for GCM validation. The ETHs calculated using velocity texture and reflectivity provide similar results, showing that the ETHs are insensitive to various techniques that can be used. Retrieved ETHs are correlated with those from cloud top heights retrieved by Multifunctional Transport Satellites (MTSATs), showing that the ETHs capture the relative variability in cloud top heights over seasonal scales. Bimodal distributions of ETH, likely attributable to the cumulus congestus clouds and mature stages of convection, are more commonly observed when the active phase of the MJO is over Australia due to greater mid-level moisture during the active phase of the MJO. The presence of a convectively stable layer at around 5 km altitude over Darwin inhibiting convection past this level can explain the position of the modes at around 2–4 km and 7–9 km. Larger cells were observed during break conditions compared to monsoon conditions, but only during the inactive phase of the MJO. The spatial distributions show that Hector, a deep convective system that occurs almost daily during the wet season over the Tiwi Islands, and sea-breeze convergence lines are likely more common in break conditions. Oceanic MCSs are more common during the night over Darwin. Convective areas were generally smaller and MCSs more frequent during active monsoon conditions. In general, the MJO is a greater control on the ETHs in the deep convective mode observed over Darwin, with higher distributions of ETH when the MJO is active over Darwin.
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Flossmann, Andrea I., Michael Manton, Ali Abshaev, Roelof Bruintjes, Masataka Murakami, Thara Prabhakaran i Zhanyu Yao. "Review of Advances in Precipitation Enhancement Research". Bulletin of the American Meteorological Society 100, nr 8 (sierpień 2019): 1465–80. http://dx.doi.org/10.1175/bams-d-18-0160.1.
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AbstractThis paper provides a summary of the assessment report of the World Meteorological Organization (WMO) Expert Team on Weather Modification that discusses recent progress on precipitation enhancement research. The progress has been underpinned by advances in our understanding of cloud processes and interactions between clouds and their environment, which, in turn, have been enabled by substantial developments in technical capabilities to both observe and simulate clouds from the microphysical to the mesoscale. We focus on the two cloud types most commonly seeded in the past: winter orographic cloud systems and convective cloud systems. A key issue for cloud seeding is the extension from cloud-scale research to water catchment–scale impacts on precipitation on the ground. Consequently, the requirements for the design, implementation, and evaluation of a catchment-scale precipitation enhancement campaign are discussed. The paper concludes by indicating the most important gaps in our knowledge. Some recommendations regarding the most urgent research topics are given to stimulate further research.
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Min, Q. L., R. Li, B. Lin, E. Joseph, S. Wang, Y. Hu, V. Morris i F. Chang. "Evidence of mineral dust altering cloud microphysics and precipitation". Atmospheric Chemistry and Physics Discussions 8, nr 6 (3.11.2008): 18893–910. http://dx.doi.org/10.5194/acpd-8-18893-2008.
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Abstract. Multi-platform and multi-sensor observations are employed to investigate the impact of mineral dust on cloud microphysical and precipitation processes in mesoscale convective systems. It is clearly evident that for a given convection strength,small hydrometeors were more prevalent in the stratiform rain regions with dust than in those regions that were dust free. Evidence of abundant cloud ice particles in the dust sector, particularly at altitudes where heterogeneous nucleation process of mineral dust prevails, further supports the observed changes of precipitation. The consequences of the microphysical effects of the dust aerosols were to shift the precipitation size spectrum from heavy precipitation to light precipitation and ultimately suppressing precipitation.
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Jeong, J. H., D. I. Lee, C. C. Wang, S. M. Jang, C. H. You i M. Jang. "Environment and morphology of mesoscale convective systems associated with the Changma front during 9–10 July 2007". Annales Geophysicae 30, nr 8 (22.08.2012): 1235–48. http://dx.doi.org/10.5194/angeo-30-1235-2012.
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Abstract. To understand the different environment and morphology for heavy rainfall during 9–10 July 2007, over the Korean Peninsula, mesoscale convective systems (MCSs) that accompanied the Changma front in two different regions were investigated. The sub-synoptic conditions were analysed using mesoscale analysis data (MANAL), reanalysis data, weather charts and Multi-functional Transport Satellite (MTSAT-IR) data. Dual-Doppler radar observations were used to analyse the wind fields within the precipitation systems. During both the case periods, the surface low-pressure field intensified and moved northeastward along the Changma front. A low-level warm front gradually formed with an east-west orientation, and the cold front near the low pressure was aligned from northeast to southwest. The northern convective systems (meso-α-scale) were embedded within an area of stratiform cloud north of the warm front. The development of low-level pressure resulted in horizontal and vertical wind shear due to cyclonic circulation. The wind direction was apparently different across the warm front. In addition, the southeasterly flow (below 4 km) played an important role in generating new convective cells behind the prevailing convective cell. Each isolated southern convective cell (meso-β-scale) moved along the line ahead of the cold front within the prefrontal warm sector. These convective cells developed when a strong southwesterly low-level jet (LLJ) intensified and moisture was deeply advected into the sloping frontal zone. A high equivalent potential temperature region transported warm moist air in a strong southwesterly flow, where the convectively unstable air led to updraft and downdraft with a strong reflectivity core.