Life Cycle Of Mesoscale Convective Systems Research Articles

The Impact of Topography on the Environment and Life Cycle of Weakly and Strongly Forced MCSs during RELAMPAGO

Abstract Intense deep convection and large mesoscale convective systems (MCSs) are known to occur downstream of the Andes in subtropical South America. Deep convection is often focused along the Sierras de Córdoba (SDC) in the afternoon and then rapidly grows upscale and moves to the east overnight. However, how the Andes and SDC impact the life cycle of MCSs under varying synoptic conditions is not well understood. Two sets of terrain-modification experiments using WRF are used to investigate the impact of topography in different synoptic regimes. The first set is run on the 13–14 December 2018 MCS case from RELAMPAGO, which featured a deep synoptic trough, strong lee cyclogenesis near the SDC, an enhanced low-level jet, and rapid upscale growth of an MCS. When the Andes are reduced by 50%, the lee cyclone and low-level jet that develop are weaker than with the full Andes, and the resulting MCS is weak and moves faster to the east. When the SDC are removed, few differences between the environment and resulting MCS relative to the control run are seen. A second set of experiments are run on the 25–26 January 2019 case in which a large MCS developed over the SDC and remained tied there for an extended period under weak synoptic forcing. The experiment that produces the most similar MCS to the control is when the Andes are reduced by 50% while maintaining the height of the SDC, suggesting the SDC may play a more important role in the MCS life cycle under quiescent synoptic conditions.

A Satellite-Based Climatology of Central and Southeastern U.S. Mesoscale Convective Systems

Abstract A satellite-based climatology is presented of 9607 mesoscale convective systems (MCSs) that occurred over the central and southeastern United States from 1996 to 2017. This climatology is constructed with a fully automated algorithm based on their cold cloud shields, as observed from infrared images taken by GOES-East satellites. The geographical, seasonal, and diurnal patterns of MCS frequency are evaluated, as are the frequency distributions and seasonal variability of duration and maximum size. MCS duration and maximum size are found to be strongly correlated, with coefficients greater than 0.7. Although previous literature has subclassified MCSs based on size and duration, we find no obvious threshold that cleanly categorizes MCSs. The Plains and Deep South are identified as two regional modes of maximum MCS frequency, accounting for 21% and 18% of MCSs, respectively, and these are found to differ in the direction and speed of the MCSs (means of 16 and 13 m s−1), their distributions of duration and size (means of 12.2 h, 176 000 km2 and 9.6 h, 108 000 km2), their initial growth rates (means of 7.6 and 6.1 km2 s−1), and many aspects of the seasonal cycle. The lifetime patterns of MCS movement and growth are evaluated for the full domain and for the two regional modes. The growth patterns and strong correlation between size and duration allow for a parabolic function to represent the MCS life cycle quite well in summary statistics. We show that this satellite-based climatology supports previous studies identifying favorable environments for mesoscale convective systems.

The microphysical contributions to and evolution of latent heating profiles in two MC3E MCSs

AbstractThe shapes and magnitudes of latent heating profiles have been shown to be different within the convective and stratiform regions of mesoscale convective systems (MCSs). Properly representing these distinctions has significant implications for the atmospheric responses to latent heating on various scales. This study details (1) the microphysical process contributions to latent heating profiles within MCS convective, stratiform, and anvil regions and (2) the time evolution of these profiles throughout the MCS lifetime, using cloud‐resolving model simulations. Simulations of two MCS events that occurred during the Midlatitude Continental Convective Clouds Experiment (MC3E) are conducted. Several features of the simulated MCSs are compared to a suite of observations obtained during the MC3E field campaign, and it is concluded that the simulations reasonably reproduce the MCS events. The simulations show that condensation and deposition are the primary contributors to MCS latent warming, as compared to riming and nucleation processes. In terms of MCS latent cooling, sublimation, melting, and evaporation all play significant roles. It is evident that throughout the MCS lifecycle, convective regions demonstrate an approximately linear decrease in the magnitudes of latent heating rates, while latent heating within stratiform regions is associated with transitions between MCS flow regimes. Such information regarding the temporal evolution of latent heating within convective and stratiform MCS regions could be useful in developing parameterizations representing convective organization.

Convective Initiation near the Andes in Subtropical South America

Abstract Satellite radar and radiometer data indicate that subtropical South America has some of the deepest and most extreme convective storms on Earth. This study uses the full 15-yr TRMM Precipitation Radar dataset in conjunction with high-resolution simulations from the Weather Research and Forecasting Model to better understand the physical factors that control the climatology of high-impact weather in subtropical South America. The occurrence of intense storms with an extreme horizontal dimension is generally associated with lee cyclogenesis and a strengthening South American low-level jet (SALLJ) in the La Plata basin. The orography of the Andes is critical, and model sensitivity calculations removing and/or reducing various topographic features indicate the orographic control on the initiation of convection and its upscale growth into mesoscale convective systems (MCSs). Reduced Andes experiments show more widespread convective initiation, weaker average storm intensity, and more rapid propagation of the MCS to the east (reminiscent of the MCS life cycle downstream of lower mountains such as the Rockies). With reduced Andes, lee cyclogenesis and SALLJ winds are weaker, while they are stronger in increased Andes runs. The presence of the Sierras de Córdoba (secondary mountain range east of the Andes in Argentina) focuses convective initiation and results in more intense storms in experiments with higher Andes. Average CAPE and CIN values for each terrain modification simulation show that reduced Andes runs had lower CIN and CAPE, while increased Andes runs had both stronger CAPE and CIN. From this research, a conceptual model for convective storm environments leading to convective initiation has been developed for subtropical South America.

항공기 안전 운항에 영향을 미치는 중규모 대류계 사례 연구(II)

Heavy Rainfall event accompanying with Mesoscale Convective Systems(MCSs) inducing flash flooding and Muan and Kunsan Airport closing over Jeollabuk-do area was investigated this study. Comparing to previous study(I), this heavy rainfall event was characterized by much abundant moisture from Typhoon, strong conditional convective instability, and cluster type MCSs. It almost impossible to make accurate forecasting of precipitation amounts and life cycle of MCSs unless proper analysis.

An automated nowcasting system of mesoscale convective systems for the Mediterranean basin using Meteosat imagery. Part I: System description

This study presents the methodologies used to develop a nowcasting system of Mesoscale Convective Systems (MCSs) over the Mediterranean region on the basis of Meteosat Second Generation (MSG) imagery. The nowcasting system is an algorithm that detects and tracks MCSs in Meteosat images and then forecasts the movement and the evolution of the physical properties of a selected MCS through its entire lifecycle, at 15 min intervals. The forecasting procedure combines a linear extrapolation method of the MCS life cycle history and information extracted from conceptual models. As a final output, the system generates a complete life cycle forecast of the temporal evolution of several physical characteristics of the MCS, such as areal extent, displacement, mean brightness temperature and convective potential, and visualizes the forecast by drawing ellipses that represent the MCS with 15 min time steps. Forecasts of a complete life cycle are updated every 15 min in accordance to the acquisition of a new satellite image.

Severe weather reports and proximity to deep convection over Northern Argentina

Conventional surface data and quantitative estimations of precipitation are used to document the occurrence and spatial distribution of severe weather phenomena associated with deep moist convection over southeastern South America. Data used in this paper are 24-hour rainfall, maximum hourly gusts and present weather reports from the surface station network for Argentina to the north of 40°S and cover the period 2000–2005. Hourly rainfall estimated with the CMORPH technique (CPC MORPHing technique, R. J. Joyce et al., 2004) is included in the analysis in order to increase the density of the precipitation database from January 2003 to December 2005. Extreme events are detected by means of a 95th-percentile analysis of the 24-hour rainfall and wind; values greater than 30 mm and 25 m s −1 respectively are considered extreme in the study area. These results are related to the presence of deep convection by considering the 235 K and 218 K cloud shield evolution in Geostationary Operational Environmental Satellite-12 Infrared (GOES-IR) imagery evaluated by the Forecasting and Tracking of Cloud Cluster (FORTRACC) technique. Rainfall above 30 mm day −1 and present convection-related weather events tend to occur in the northeast of the country. Finally, an analysis is made of the relationship between severe phenomena and the location and lifecycle of Mesoscale Convective Systems (MCSs) defined by the 218 K or 235 K levels. According to the reports, favorable locations for severe weather concentrate to the northeast of the cloud shield anvil centroid although most of the cases are found in the northwest. This feature can be seen in systems with anvil areas larger than 250,000 km 2 in association to the predominant mid-level wind shear direction from the northwest over the area. Moreover, systems with centers located north of 30°S present a more circular shape while those to the south are more elongated with a NW–SE main axis clearly related to the presence and interaction with frontal zones over the area. Most of the events occur previous to the moment when the systems reach their maximum extension, between 2 and 10 h after the initiation of the system depending on the size of the MCSs.

Microphysical and Thermodynamic Structure and Evolution of the Trailing Stratiform Regions of Mesoscale Convective Systems during BAMEX. Part I: Observations

Abstract This study used airborne and ground-based radar and optical array probe data from the spiral descent flight patterns and horizontal flight legs of the NOAA P-3 aircraft in the trailing stratiform regions (TSRs) of mesoscale convective systems (MCSs) observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) to characterize microphysical and thermodynamic variations within the TSRs in the context of the following features: the transition zone, the notch region, the enhanced stratiform rain region, the rear anvil region, the front-to-rear flow, the rear-to-front flow, and the rear inflow jet axis. One spiral from the notch region, nine from the enhanced stratiform rain region, and two from the rear anvil region were analyzed along with numerous horizontal flight legs that traversed these zones. The spiral performed in the notch region on 29 June occurred early in the MCS life cycle and exhibited subsaturated conditions throughout its depth. The nine spirals performed within the enhanced stratiform rain region exhibited saturated conditions with respect to ice above and within the melting layer and subsaturated conditions below the melting layer. Spirals performed in the rear anvil region showed saturation until the base of the anvil, near −1°C, and subsaturation below. These data, together with analyses of total number concentration and the slope to gamma fits to size distributions, revealed that sublimation above the melting layer occurs early in the MCS life cycle but then reduces in importance as the environment behind the convective line is moistened from the top down. Evaporation below the melting layer was insufficient to attain saturation below the melting layer at any time or location within the MCS TSRs. Relative humidity was found to have a strong correlation to the component of wind parallel to the storm motion, especially within air flowing from front to rear.

Basis for a Rainfall Estimation Technique Using IR–VIS Cloud Classification and Parameters over the Life Cycle of Mesoscale Convective Systems

Abstract This paper discusses the basis for a new rainfall estimation method using geostationary infrared and visible data. The precipitation radar on board the Tropical Rainfall Measuring Mission satellite is used to train the algorithm presented (which is the basis of the estimation method) and the further intercomparison. The algorithm uses daily Geostationary Operational Environmental Satellite infrared–visible (IR–VIS) cloud classifications together with radiative and evolution properties of clouds over the life cycle of mesoscale convective systems (MCSs) in different brightness temperature (Tb) ranges. Despite recognition of the importance of the relationship between the life cycle of MCSs and the rainfall rate they produce, this relationship has not previously been quantified precisely. An empirical relationship is found between the characteristics that describe the MCSs’ life cycle and the magnitude of rainfall rate they produce. Numerous earlier studies focus on this subject using cloud-patch or pixel-based techniques; this work combines the two techniques. The algorithm performs reasonably well in the case of convective systems and also for stratiform clouds, although it tends to overestimate rainfall rates. Despite only using satellite information to initialize the algorithm, satisfactory results were obtained relative to the hydroestimator technique, which in addition to the IR information uses extra satellite data such as moisture and orographic corrections. This shows that the use of IR–VIS cloud classification and MCS properties provides a robust basis for creating a future estimation method incorporating humidity Eta field outputs for a moisture correction, digital elevation models combined with low-level moisture advection for an orographic correction, and a nighttime cloud classification.

Oceanic Cyclogenesis as Induced by a Mesoscale Convective System Moving Offshore. Part II: Genesis and Thermodynamic Transformation

The genesis of intense cyclonic vorticity in the boundary layer and the transformation of a low-level cold pool to a warm-core anomaly associated with the long-lived mesoscale convective systems (MCSs), which produced the July 1977 Johnstown flash flood and later developed into a tropical storm, are examined using a 90-h real-data simulation of the evolution from a continental MCS/vortex to an oceanic cyclone/storm system. It is shown that the midlevel vortex/trough at the end of the continental MCS's life cycle is characterized by a warm anomaly above and a cold anomaly below. The mesovortex, as it drifts toward the warm Gulf Stream water, plays an important role in initiating and organizing a new MCS and a cyclonic (shear) vorticity band at the southern periphery of the previously dissipated MCS. It is found from the vorticity budget that the vorticity band is amplified through stretching of absolute vorticity as it is wrapped around in a slantwise manner toward the cyclone center. Then, the associated shear vorticity is converted to curvature vorticity near the center, leading to the formation of a “comma-shaped” vortex and the rapid spinup of the surface cyclone to tropical storm intensity. Thermodynamic budgets reveal that the vertical transfer of surface fluxes from the warm ocean and the convectively induced grid-scale transport are responsible for the development of a high-θe tongue, which is wrapped around in a fashion similar to the vorticity band, causing conditional instability and further organization of the convective storm. Because the genesis occurs at the southern periphery of the vortex/trough, the intensifying cyclonic circulation tends to advect the pertinent cold air in the north-to-northwesterly flow into the convective storm and the ambient warmer air into the cyclone center, thereby transforming the low-level cold anomaly to a warm-cored structure near the cyclone core. It is shown that the transformation and the evolution of the surface cyclone are mainly driven by the low-level vorticity concentrations. It is found that many of the cyclogenesis scenarios in the present case are similar to those noted in previous tropical cyclogenesis studies and observed at the early stages of tropical cyclogenesis from MCSs during the Tropical Experiment in Mexico. Therefore, the results have significant implications with regard to tropical cyclogenesis from MCSs.