scholarly journals Microphysical and Thermodynamic Structure and Evolution of the Trailing Stratiform Regions of Mesoscale Convective Systems during BAMEX. Part II: Column Model Simulations

2009 ◽  
Vol 137 (4) ◽  
pp. 1186-1205 ◽  
Author(s):  
Joseph A. Grim ◽  
Greg M. McFarquhar ◽  
Robert M. Rauber ◽  
Andrea M. Smith ◽  
Brian F. Jewett
Keyword(s):  
Mesoscale Convective Systems ◽  
Sharp Change ◽  
Melting Layer ◽  
Thermodynamic Structure ◽  
Column Model ◽  
Convective Systems ◽  
Stratiform Region ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Microphysical Processes

Abstract This study employed a nondynamic microphysical column model to evaluate the degree to which the microphysical processes of sublimation, melting, and evaporation alone can explain the evolution of the relative humidity (RH) and latent cooling profiles within the trailing stratiform region of mesoscale convective systems observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). Simulations revealed that observations of a sharp change in the profile of RH, from saturated air with respect to ice above the melting layer to subsaturated air with respect to water below, developed in response to the rapid increase in hydrometeor fall speeds from 1–2 m s−1 for ice to 2–11 m s−1 for rain. However, at certain times and locations, such as the first spiral descent on 29 June 2003 within the notch of lower reflectivity, the air may remain subsaturated for temperatures (T) < 0°C. Sufficiently strong downdrafts above the melting level, such as the 1–3 m s−1 downdrafts observed in the notch of lower reflectivity on 29 June, could enable this state of sustained subsaturation. Sensitivity tests, where the hydrometeor size distributions and upstream RH profiles were varied within the range of BAMEX observations, revealed that the sharp contrast in the RH field across the melting layer always developed. The simulations also revealed that latent cooling from sublimation and melting resulted in the strongest cooling at altitudes within and above the melting layer for locations where hydrometeors did not reach the ground, such as within the rear anvil region, and where sustained subsaturated air is present for T < 0°C, such as is observed within downdrafts. Within the enhanced stratiform rain region, the air is typically at or near saturation for T < 0°C, whereas it is typically subsaturated for T > 0°C; thus, evaporation and melting result in the primary cooling in this region. The implications of these results for the descent of the rear inflow jet across the trailing stratiform region are discussed.

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

2009 ◽  
Vol 137 (4) ◽  
pp. 1165-1185 ◽  
Author(s):  
Andrea M. Smith ◽  
Greg M. McFarquhar ◽  
Robert M. Rauber ◽  
Joseph A. Grim ◽  
Michael S. Timlin ◽  
...  
Keyword(s):  
Life Cycle ◽  
Mesoscale Convective Systems ◽  
Melting Layer ◽  
Thermodynamic Structure ◽  
Stratiform Rain ◽  
Convective Systems ◽  
Horizontal Flight ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Mesoscale Convective Vortex

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.

scholarly journals Thermodynamic Properties of Mesoscale Convective Systems Observed during BAMEX

2008 ◽  
Vol 136 (11) ◽  
pp. 4242-4271 ◽  
Author(s):  
James Correia ◽  
Raymond W. Arritt
Keyword(s):  
Potential Temperature ◽  
Mesoscale Convective Systems ◽  
Lapse Rate ◽  
Spatiotemporal Variability ◽  
Cold Pool ◽  
Convective Systems ◽  
Stratiform Region ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Lapse Rates

Abstract Dropsonde observations from the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) are used to document the spatiotemporal variability of temperature, moisture, and wind within mesoscale convective systems (MCSs). Onion-type sounding structures are found throughout the stratiform region of MCSs, but the temperature and moisture variability is large. Composite soundings were constructed and statistics of thermodynamic variability were generated within each subregion of the MCS. The calculated air vertical velocity helped identify subsaturated downdrafts. It was found that lapse rates within the cold pool varied markedly throughout the MCS. Layered wet-bulb potential temperature profiles seem to indicate that air within the lowest several kilometers comes from a variety of source regions. It was also found that lapse-rate transitions across the 0°C level were more common than isothermal, melting layers. The authors discuss the implications these findings have and how they can be used to validate future high-resolution numerical simulations of MCSs.

Precipitation charge and size measurements in the stratiform region of two mesoscale convective systems

1995 ◽  
Vol 100 (D8) ◽  
pp. 16341 ◽  
Author(s):  
Monte G. Bateman ◽  
W. David Rust ◽  
Bradley F. Smull ◽  
Thomas C. Marshall
Keyword(s):  
Mesoscale Convective Systems ◽  
Convective Systems ◽  
Stratiform Region ◽  
Mesoscale Convective

Impact of Convectively Generated Low-Frequency Gravity Waves on Evolution of Mesoscale Convective Systems

2020 ◽  
Vol 77 (10) ◽  
pp. 3441-3460
Author(s):  
Rebecca D. Adams-Selin
Keyword(s):  
Gravity Waves ◽  
Low Frequency ◽  
Mesoscale Convective Systems ◽  
Cloud Base ◽  
Mature Stage ◽  
First Order ◽  
Convective Systems ◽  
Stratiform Region ◽  
Mesoscale Convective ◽  
Wave Modes

AbstractIdealized numerical simulations of mesoscale convective systems (MCSs) over a range of instabilities and shears were conducted to examine low-frequency gravity waves generated during initial and mature stages of convection. In all simulations, at initial updraft development a first-order wave was generated by heating extending through the depth of the troposphere. Additional first-order wave modes were generated each time the convective updraft reintensified. Each of these waves stabilized the environment in advance of the system. As precipitation descended below cloud base, and as a stratiform precipitation region developed, second-order wave modes were generated by cooling extending from the midlevels to the surface. These waves destabilized the environment ahead of the system but weakened the 0–5 km shear. Third-order wave modes could be generated by midlevel cooling caused by rear inflow intensification; these wave modes cooled the midlevels destabilizing the environment. The developing stage of each MCS was characterized by a cyclical process: developing updraft, generation of n = 1 wave, increase in precipitation, generation of n = 2 wave, and subsequent environmental destabilization reinvigorating the updraft. After rearward expansion of the stratiform region, the MCSs entered their mature stage and the method of updraft reinvigoration shifted to absorbing discrete convective cells produced in advance of each system. Higher-order wave modes destabilized the environment, making it more favorable to development of these cells and maintenance of the MCS. As initial simulation shear or instability increased, the transition from cyclical wave/updraft development to discrete cell/updraft development occurred more quickly.

scholarly journals Inferring microphysical processes occurring in mesoscale convective systems from radar measurements and isotopic analysis

2008 ◽  
Vol 35 (9) ◽  
Author(s):  
T. Narayana Rao ◽  
B. Radhakrishna ◽  
Rohit Srivastava ◽  
T. Mohan Satyanarayana ◽  
D. Narayana Rao ◽  
...  
Keyword(s):  
Isotopic Analysis ◽  
Mesoscale Convective Systems ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Radar Measurements ◽  
Microphysical Processes

scholarly journals Vertical Variability of Cloud Hydrometeors in the Stratiform Region of Mesoscale Convective Systems and Bow Echoes

2007 ◽  
Vol 135 (10) ◽  
pp. 3405-3428 ◽  
Author(s):  
Greg M. McFarquhar ◽  
Michael S. Timlin ◽  
Robert M. Rauber ◽  
Brian F. Jewett ◽  
Joseph A. Grim ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Slope Parameter ◽  
Melting Layer ◽  
Ambient Relative Humidity ◽  
Minimum Relative Humidity ◽  
Stratiform Region ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
The Impact ◽  
Vertical Variability

Abstract During the Bow Echo and Mesoscale Convective Vortex Experiment, the NOAA P-3 research aircraft executed 17 spiral descents to the rear of convective lines to document the vertical variability of hydrometeors above, within, and below the stratiform melting layer. Ten spirals were behind lines that exhibited bowing at some stage in their evolution. Although quick descents on some spirals forced sampling of different particle zones, clear trends with respect to temperature were seen. For 16 spirals, the ambient relative humidity with respect to ice was in the range of 100% ± 4% at temperatures between −10°C and the melting layer, but exhibited steady decreases below the melting layer to an average relative humidity with respect to water of 77% ± 15% at 9°C. In contrast, one spiral conducted on 29 June 2003 directly behind a developing bow echo had a relative humidity with respect to ice averaging 85% at heights above the 0°C level and relative humidity with respect to ice further decreased below the 0°C level to a minimum relative humidity with respect to water of 48% at 9°C. Vertical profiles of particle shapes, size distributions (SDs), total mass contents (TMC), number concentrations, and parameters of gamma distributions fit to SDs were computed using optical array probe data in conjunction with measurements of radar reflectivity from the P-3 X-band tail radar. For spirals with humidity at or near saturation above the melting layer, melting particles occurred through about 300 m of cloud depth between 0° and 2° or 3°C. Above the melting layer, number concentrations, dominated by smaller crystals, decreased at 19% ± 10% °C−1, faster than the 10% ± 7% °C−1 decrease of TMC dominated by larger particles. Increases in the numbers of crystals with a maximum dimension <2 mm (N<2) and in the slope parameter with temperature also occurred. To the extent that in-cloud heterogeneity did not complicate observed trends, these trends suggest aggregation dominated the evolution of SDs. Observations on 29 June differ from other days and are explained by the unique position and timing of the spiral in subsaturated air behind a developing bow. On 29 June the presence of an isothermal layer at 2.5°C suggested that sublimative cooling delayed the onset of melting. Ice at 7°C showed that melting particles were present through 500 m of cloud depth. A slight decrease in N<2, but no decrease in the slope parameter, with temperature suggested that sublimation modified the impact of aggregation. Sublimative cooling would only have been significant at the location of the 29 June spiral. For other spirals, evaporative cooling below the melting layer in subsaturated regions was the most important diabatic processes in the stratiform regions at the time of the observations.

scholarly journals Total Lightning Signatures of Thunderstorm Intensity over North Texas. Part II: Mesoscale Convective Systems

2007 ◽  
Vol 135 (10) ◽  
pp. 3303-3324 ◽  
Author(s):  
Scott M. Steiger ◽  
Richard E. Orville ◽  
Lawrence D. Carey
Keyword(s):  
Mesoscale Convective Systems ◽  
Research Network ◽  
Fort Worth ◽  
Convective Systems ◽  
Source Density ◽  
Stratiform Region ◽  
Straight Line ◽  
Lightning Detection ◽  
Mesoscale Convective ◽  
Total Lightning

Abstract Total lightning data from the Lightning Detection and Ranging (LDAR II) research network in addition to cloud-to-ground flash data from the National Lightning Detection Network (NLDN) and data from the Dallas–Fort Worth, Texas, Weather Surveillance Radar-1988 Doppler (WSR-88D) station (KFWS) were examined from individual cells within mesoscale convective systems that crossed the Dallas–Fort Worth region on 13 October 2001, 27 May 2002, and 16 June 2002. LDAR II source density contours were comma shaped, in association with severe wind events within mesoscale convective systems (MCSs) on 13 October 2001 and 27 May 2002. This signature is similar to the radar reflectivity bow echo. The source density comma shape was apparent 15 min prior to a severe wind report and lasted more than 20 min during the 13 October storm. Consistent relationships between severe straight-line winds, radar, and lightning storm cell characteristics (e.g., lightning heights) were not found for cells within MCSs as was the case for severe weather in supercells in Part I of this study. Cell interactions within MCSs are believed to weaken these relationships as reflectivity and lightning from nearby storms contaminate the cells of interest. Another hypothesis for these weak relations is that system, not individual cell, processes are responsible for severe straight-line winds at the surface. Analysis of the total lightning structure of the 13 October 2001 MCS showed downward-sloping source density contours behind the main convective line into the stratiform region. This further supports a charge advection mechanism in developing the stratiform charge structure. Bimodal vertical source density distributions were observed within MCS convection close to the center of the LDAR II network, while the lower mode was not detected at increasing range.

scholarly journals The Mesoscale Convective Systems with bow echo radar signatures as an example of extremely severe and widespread geohazard in Poland

2018 ◽  
Vol 6 (1) ◽  
pp. 10-16 ◽  
Author(s):  
Artur Widawski ◽  
Wojciech Pilorz
Keyword(s):  
Radar Reflectivity ◽  
Mesoscale Convective Systems ◽  
Material Damage ◽  
Pressure System ◽  
Convective Systems ◽  
Radar Images ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Strong Winds ◽  
Echo Radar

AbstractIn the last two decades we can notice a significant increase of severe anemological events, which are mostly connected with mesoscale convective systems and a cold front of a deep low-pressure system. One of them are very strong winds with speeds more than 25 m/s. They caused material damage and threatening people's lives. The most dangerous are winds generated by mesoscale convective systems where radar reflectivity signatures of bow echo/derecho appeared. In this paper the area of occurrence of such phenomenon in Poland are described and the features of bow echo signatures on radar images are presented and explained. Additionally one of the most severe event and still very weakly known episode of 11th August 2017 derecho in Poland is analysed. The damage data from European Severe Weather Database (ESWD) were analysed to confirm if the August 11th storm met derecho criteria. To identify the radar reflectivity signatures inside MCC the data from the Polish Institute of Meteorology and Water Management shared on the radar-opadow.pl site were used. The CAPPI 1 km data were very useful to determine the convective forms. After that the data from synoptic station were examined for presenting the running of selected meteorological elements. Finally, some information about material damage in infrastructures and forests are mentioned.

Baroclinic Transition of a Long-Lived Mesoscale Convective Vortex

2009 ◽  
Vol 137 (2) ◽  
pp. 562-584 ◽  
Author(s):  
Thomas J. Galarneau ◽  
Lance F. Bosart ◽  
Christopher A. Davis ◽  
Ron McTaggart-Cowan
Keyword(s):  
Heavy Precipitation ◽  
Transition Process ◽  
Sea Level Pressure ◽  
Convective Systems ◽  
Stratiform Region ◽  
Surface Cyclone ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Baroclinic Energy Conversion ◽  
Mesoscale Convective Vortex

Abstract The period 5–15 June 2003, during the field phase of the Bow Echo and Mesoscale Convective Vortex (MCV) Experiment (BAMEX), was noteworthy for the wide variety of mesoscale convective systems (MCSs) that occurred. Of particular interest was a long-lived MCV that formed in the trailing stratiform region of an MCS over west Texas at 0600 UTC 10 June. This MCV was noteworthy for its (i) longevity as it can be tracked from 0600 UTC 10 June to 1200 UTC 14 June, (ii) development of a surface cyclonic circulation and attendant −2- to −4-hPa sea level pressure perturbation, (iii) ability to retrigger convection and produce widespread rains over several diurnal heating cycles, and (iv) transition into a baroclinic surface cyclone with distinct frontal features. Baroclinic transition, defined here as the acquisition of surface fronts, occurred as the MCV interacted with a remnant cold front, left behind by a predecessor extratropical cyclone, over the Great Lakes region. Although the MCV developed well-defined frontal structure, which helped to focus heavy precipitation, weakening occurred throughout the baroclinic transition process. Energetics calculations indicated that weakening occurred as the diabatic and baroclinic energy conversion terms approached zero just prior and during baroclinic transition. This weakening can be attributed to (i) an increase in environmental wind shear, (ii) the development of a downshear tilt and associated anticyclonic vorticity advection over the surface low center, and (iii) the eastward relative movement of organized convection away from the MCV center.

scholarly journals A Simple Lagrangian Parcel Model for the Initiation of Summer-time Mesoscale Convective Systems over the Central United States

2021 ◽  
Author(s):  
Qiu Yang ◽  
L. Ruby Leung ◽  
Zhe Feng ◽  
Fengfei Song ◽  
Xingchao Chen
Keyword(s):  
United States ◽  
Simple Model ◽  
Mesoscale Convective Systems ◽  
Cold Pool ◽  
Column Model ◽  
Convective Systems ◽  
Single Column ◽  
Central United States ◽  
Mesoscale Convective ◽  
Summer Time

AbstractMesoscale convective systems (MCSs) account for more than 50% of summer-time precipitation over the central United States (US) and have a significant impact on local weather and hydrologic cycle. It is hypothesized that the inadequate treatment of MCSs is responsible for the longstanding warm and dry bias over the central US in coarse-resolution general circulation model (GCM) simulations. In particular, a better understanding of MCS initiation is still lacking. Here a single-column Lagrangian parcel model is first developed to simulate the basic features of a rising parcel. This simple model demonstrates the collective effects of boundary layer moistening and dynamical lifting in triggering convective initiation and reproduces successfully its early afternoon peak with surface equivalent potential temperature as a controlling factor. It also predicts that convection is harder to trigger in the future climate under global warming, consistent with the results from convection-permitting regional climate simulations. Then a multi-column model that includes an array of single-column models aligned in the east-west direction and incorporates idealized cold pool interaction mechanisms is developed. The multi-column model captures readily the cold pool induced upscale growth feature in MCS genesis from initially scattered convection that is organized into a mesoscale cluster in a few hours. It also highlights the crucial role of lifting effects due to cold pool collision and spreading, subsidence effect, and gust front propagation speed in controlling the final size of mesoscale clusters and cold pool regions. This simple model should be useful for understanding fundamental mechanisms of MCS initiation and providing guidance for improving MCS simulations in GCMs.

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