scholarly journals Evaluation of Mesoscale Convective Systems in Climate Simulations: Methodological Development and Results from MPAS-CAM over the U.S.

2020 ◽  
pp. 1-62
Author(s):  
Zhe Feng ◽  
Fengfei Song ◽  
Koichi Sakaguchi ◽  
L. Ruby Leung
Keyword(s):  
Large Scale ◽  
Precipitation Amount ◽  
Tracking Algorithm ◽  
Convective System ◽  
Low Level ◽  
Climate Simulations ◽  
Mesoscale Convective ◽  
Process Oriented ◽  
The U.S ◽  
Oriented Approach

AbstractA process-oriented approach is developed to evaluate warm-season mesoscale convective system (MCS) precipitation and their favorable large-scale meteorological patterns (FLSMPs) over the U.S. This approach features a novel observation-driven MCS-tracking algorithm using infrared brightness temperature and precipitation feature at 12, 25 and 50 km resolution and metrics to evaluate the model large-scale environment favorable for MCS initiation. The tracking algorithm successfully reproduces the observed MCS statistics from a reference 4-km radar MCS database. To demonstrate the utility of the new methodologies in evaluating MCS in climate simulations with mesoscale resolution, the process-oriented approach is applied to two climate simulations produced by the Variable-Resolution Model for Prediction Across Scales coupled to the Community Atmosphere Model physics, with refined horizontal grid spacing at 50 km and 25 km over North America. With the tracking algorithm applied to simulations and observations at equivalent resolutions, the simulated number of MCS and associated precipitation amount, frequency and intensity are found to be consistently underestimated in the Central U.S., particularly from May to August. The simulated MCS precipitation shows little diurnal variation and lasts too long, while MCS precipitation area is too large and intensity is too weak. The model is able to simulate four types of observed FLSMP associated with frontal systems and low-level jets (LLJ) in spring, but the frequencies are underestimated because of low-level dry bias and weaker LLJ. Precipitation simulated under different FLSMPs peak during daytime, in contrast to the observed nocturnal peak. Implications of these findings for future model development and diagnostics are discussed.

Growth of Mesoscale Convective Systems in Observations and a Seasonal Convection-Permitting Simulation over Argentina

2021 ◽  
Vol 149 (10) ◽  
pp. 3469-3490
Author(s):  
Zhixiao Zhang ◽  
Adam Varble ◽  
Zhe Feng ◽  
Joseph Hardin ◽  
Edward Zipser
Keyword(s):  
Growth Rate ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Vertical Motion ◽  
Rain Gauge ◽  
Convective System ◽  
Low Level ◽  
Environmental Controls ◽  
Mesoscale Convective ◽  
Rain Rates

AbstractA 6.5-month, convection-permitting simulation is conducted over Argentina covering the Remote Sensing of Electrification, Lightning, And Mesoscale/Microscale Processes with Adaptive Ground Observations and Clouds, Aerosols, and Complex Terrain Interactions (RELAMPAGO-CACTI) field campaign and is compared with observations to evaluate mesoscale convective system (MCS) growth prediction. Observed and simulated MCSs are consistently identified, tracked, and separated into growth, mature, and decay stages using top-of-the-atmosphere infrared brightness temperature and surface rainfall. Simulated MCS number, lifetime, seasonal and diurnal cycles, and various cloud-shield characteristics including growth rate are similar to those observed. However, the simulation produces smaller rainfall areas, greater proportions of heavy rainfall, and faster system propagations. Rainfall area is significantly underestimated for long-lived MCSs but not for shorter-lived MCSs, and rain rates are always overestimated. These differences result from a combination of model and satellite retrieval biases, in which simulated MCS rain rates are shifted from light to heavy, while satellite-retrieved rainfall is too frequent relative to rain gauge estimates. However, the simulation reproduces satellite-retrieved MCS cloud-shield evolution well, supporting its usage to examine environmental controls on MCS growth. MCS initiation locations are associated with removal of convective inhibition more than maximized low-level moisture convergence or instability. Rapid growth is associated with a stronger upper-level jet (ULJ) and a deeper northwestern Argentinean low that causes a stronger northerly low-level jet (LLJ), increasing heat and moisture fluxes, low-level vertical wind shear, baroclinicity, and instability. Sustained growth corresponds to similar LLJ, baroclinicity, and instability conditions but is less sensitive to the ULJ, large-scale vertical motion, or low-level shear. Growth sustenance controls MCS maximum extent more than growth rate.

scholarly journals Structure of Highly Sheared Tropical Storm Chantal during CAMEX-4

2006 ◽  
Vol 63 (1) ◽  
pp. 268-287 ◽  
Author(s):  
G. M. Heymsfield ◽  
Joanne Simpson ◽  
J. Halverson ◽  
L. Tian ◽  
E. Ritchie ◽  
...  
Keyword(s):  
Large Scale ◽  
Mesoscale Convective System ◽  
Tropical Storm ◽  
Vertical Shear ◽  
Convective System ◽  
Low Level ◽  
Convective Scale ◽  
Mesoscale Convective ◽  
Upper Level ◽  
The Individual

Abstract Tropical Storm Chantal during August 2001 was a storm that failed to intensify over the few days prior to making landfall on the Yucatan Peninsula. An observational study of Tropical Storm Chantal is presented using a diverse dataset including remote and in situ measurements from the NASA ER-2 and DC-8 and the NOAA WP-3D N42RF aircraft and satellite. The authors discuss the storm structure from the larger-scale environment down to the convective scale. Large vertical shear (850–200-hPa shear magnitude range 8–15 m s−1) plays a very important role in preventing Chantal from intensifying. The storm had a poorly defined vortex that only extended up to 5–6-km altitude, and an adjacent intense convective region that comprised a mesoscale convective system (MCS). The entire low-level circulation center was in the rain-free western side of the storm, about 80 km to the west-southwest of the MCS. The MCS appears to have been primarily the result of intense convergence between large-scale, low-level easterly flow with embedded downdrafts, and the cyclonic vortex flow. The individual cells in the MCS such as cell 2 during the period of the observations were extremely intense, with reflectivity core diameters of 10 km and peak updrafts exceeding 20 m s−1. Associated with this MCS were two broad subsidence (warm) regions, both of which had portions over the vortex. The first layer near 700 hPa was directly above the vortex and covered most of it. The second layer near 500 hPa was along the forward and right flanks of cell 2 and undercut the anvil divergence region above. There was not much resemblance of these subsidence layers to typical upper-level warm cores in hurricanes that are necessary to support strong surface winds and a low central pressure. The observations are compared to previous studies of weakly sheared storms and modeling studies of shear effects and intensification. The configuration of the convective updrafts, low-level circulation, and lack of vertical coherence between the upper- and lower-level warming regions likely inhibited intensification of Chantal. This configuration is consistent with modeled vortices in sheared environments, which suggest the strongest convection and rain in the downshear left quadrant of the storm, and subsidence in the upshear right quadrant. The vertical shear profile is, however, different from what was assumed in previous modeling in that the winds are strongest in the lowest levels and the deep tropospheric vertical shear is on the order of 10–12 m s−1.

scholarly journals Dynamics Governing a Simulated Mesoscale Convective System with a Training Convective Line

2016 ◽  
Vol 73 (7) ◽  
pp. 2643-2664 ◽  
Author(s):  
John M. Peters ◽  
Russ S. Schumacher
Keyword(s):  
Large Scale ◽  
Mesoscale Convective System ◽  
Cold Pool ◽  
Convective System ◽  
Low Level ◽  
Lateral Boundary Conditions ◽  
Mesoscale Convective ◽  
Western Side ◽  
Outflow Boundary ◽  
Stationary Behavior

Abstract This research investigates the dynamics of a simulated training line/adjoining stratiform (TL/AS) mesoscale convective system (MCS), with composite atmospheric fields used as initial and lateral boundary conditions for the simulation. An initial forward-propagating MCS developed within a region of elevated convective instability and low-level lifting associated with warm-air advection along the terminus of the low-level jet. The environmental conditions external to the MCS continued to provide lift, moisture, and instability to the western side of the forward-propagating MCS, and these conditions were initially responsible for backbuilding on the system’s western side. Most parcels that encountered the southwestern outflow boundary were lifted insufficiently far to reach their levels of free convection (LFCs), and their LFC heights were increased by latent heating above them. These parcels continued northeastward beyond the surface outflow boundary (OFB), were gradually lifted, and initiated convection 80–100 km beyond encountering the OFB. Eventually the surface cold pool became sufficiently deep so that gradual ascent of parcels with moisture and instability over the OFB began initiating new convection close to the OFB—this drove backbuilding during the later portion of the MCS lifetime. These results disentangle the relative contributions of large-scale environmental factors and storm-scale processes on the quasi-stationary behavior of the MCS and show that both contributed to upstream backbulding at different times during the MCS life cycle.

Contrasting Spring and Summer Large-Scale Environments Associated with Mesoscale Convective Systems over the U.S. Great Plains

2019 ◽  
Vol 32 (20) ◽  
pp. 6749-6767 ◽  
Author(s):  
Fengfei Song ◽  
Zhe Feng ◽  
L. Ruby Leung ◽  
Robert A. Houze Jr. ◽  
Jingyu Wang ◽  
...  
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
Explanatory Power ◽  
Convective Available Potential Energy ◽  
Precipitation Amount ◽  
Mesoscale Convective Systems ◽  
Self Organizing Maps ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
The U.S

Abstract Mesoscale convective systems (MCSs) are frequently observed over the U.S. Great Plains during boreal spring and summer. Here, four types of synoptically favorable environments for spring MCSs and two types each of synoptically favorable and unfavorable environments for summer MCSs are identified using self-organizing maps (SOMs) with inputs from observational data. During spring, frontal systems providing a lifting mechanism and an enhanced Great Plains low-level jet (GPLLJ) providing anomalous moisture are important features identified by SOM analysis for creating favorable dynamical and thermodynamic environments for MCS development. During summer, the composite MCS environment shows small positive convective available potential energy (CAPE) and convective inhibition (CIN) anomalies, which are in stark contrast with the large positive CAPE and negative CIN anomalies in spring. This contrast suggests that summer convection may occur even with weak large-scale dynamical and thermodynamic perturbations so MCSs may be inherently less predictable in summer. The two synoptically favorable environments identified in summer have frontal characteristics and an enhanced GPLLJ, but both shift north compared to spring. The two synoptically unfavorable environments feature enhanced upper-level ridges, but differ in the strength of the GPLLJ. In both seasons, MCS precipitation amount, area, and rate are much larger in the frontal-related MCSs than in nonfrontal MCSs. A large-scale index constructed using pattern correlation between large-scale environments and the synoptically favorable SOM types is found to be skillful for estimating MCS number, precipitation rate, and area in spring, but its explanatory power decreases significantly in summer. The low predictability of summer MCSs deserves further investigation in the future.

scholarly journals Origin and Maintenance of the Long-Lasting, Outer Mesoscale Convective System in Typhoon Fengshen (2008)

2014 ◽  
Vol 142 (8) ◽  
pp. 2838-2859 ◽  
Author(s):  
Buo-Fu Chen ◽  
Russell L. Elsberry ◽  
Cheng-Shang Lee
Keyword(s):  
Inner Core ◽  
Outer Region ◽  
Vertical Wind Shear ◽  
Leading Edge ◽  
Cold Pool ◽  
Convective System ◽  
Rain Area ◽  
Characteristic Structure ◽  
Low Level ◽  
Mesoscale Convective

Abstract Outer mesoscale convective systems (OMCSs) are long-lasting, heavy rainfall events separate from the inner-core rainfall that have previously been shown to occur in 22% of western North Pacific tropical cyclones (TCs). Environmental conditions accompanying the development of 62 OMCSs are contrasted with the conditions in TCs that do not include an OMCS. The development, kinematic structure, and maintenance mechanisms of an OMCS that occurred to the southwest of Typhoon Fengshen (2008) are studied with Weather Research and Forecasting Model simulations. Quick Scatterometer (QuikSCAT) observations and the simulations indicate the low-level TC circulation was deflected around the Luzon terrain and caused an elongated, north–south moisture band to be displaced to the west such that the OMCS develops in the outer region of Fengshen rather than spiraling into the center. Strong northeasterly vertical wind shear contributed to frictional convergence in the boundary layer, and then the large moisture flux convergence in this moisture band led to the downstream development of the OMCS when the band interacted with the monsoon flow. As the OMCS developed in the region of low-level monsoon westerlies and midlevel northerlies associated with the outer circulation of Fengshen, the characteristic structure of a rear-fed inflow with a leading stratiform rain area in the cross-line direction (toward the south) was established. A cold pool (Δθ < −3 K) associated with the large stratiform precipitation region led to continuous formation of new cells at the leading edge of the cold pool, which contributed to the long duration of the OMCS.

scholarly journals An Analysis of Moisture Fluxes into the Gulf of California

2009 ◽  
Vol 22 (8) ◽  
pp. 2216-2239 ◽  
Author(s):  
Man-Li C. Wu ◽  
Siegfried D. Schubert ◽  
Max J. Suarez ◽  
Norden E. Huang
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Gulf Of California ◽  
Large Scale ◽  
Moisture Flux ◽  
Easterly Waves ◽  
Low Level ◽  
Moisture Fluxes ◽  
The Caribbean ◽  
The U.S

Abstract This study examines the nature of episodes of enhanced warm-season moisture flux into the Gulf of California. Both spatial structure and primary time scales of the fluxes are examined using the 40-yr ECMWF Re-Analysis data for the period 1980–2001. The analysis approach consists of a compositing technique that is keyed on the low-level moisture fluxes into the Gulf of California. The results show that the fluxes have a rich spectrum of temporal variability, with periods of enhanced transport over the gulf linked to African easterly waves on subweekly (3–8 day) time scales, the Madden–Julian oscillation (MJO) at intraseasonal time scales (20–90 day), and intermediate (10–15 day) time-scale disturbances that appear to originate primarily in the Caribbean Sea–western Atlantic Ocean. In the case of the MJO, enhanced low-level westerlies and large-scale rising motion provide an environment that favors large-scale cyclonic development near the west coast of Central America that, over the course of about 2 weeks, expands northward along the coast eventually reaching the mouth of the Gulf of California where it acts to enhance the southerly moisture flux in that region. On a larger scale, the development includes a northward shift in the eastern Pacific ITCZ, enhanced precipitation over much of Mexico and the southwestern United States, and enhanced southerly/southeasterly fluxes from the Gulf of Mexico into Mexico and the southwestern and central United States. In the case of the easterly waves, the systems that reach Mexico appear to redevelop/reorganize on the Pacific coast and then move rapidly to the northwest to contribute to the moisture flux into the Gulf of California. The most intense fluxes into the gulf on these time scales appear to be synchronized with a midlatitude short-wave trough over the U.S. West Coast and enhanced low-level southerly fluxes over the U.S. Great Plains. The intermediate (10–15 day) time-scale systems have zonal wavelengths roughly twice that of the easterly waves, and their initiation appears to be linked to an extratropical U.S. East Coast ridge and associated northeasterly winds that extend well into the Caribbean Sea during their development phase. The short (3–8 day) and, to a lesser extent, the intermediate (10–15 day) time-scale fluxes tend to be enhanced when the convectively active phase of the MJO is situated over the Americas.

scholarly journals Mesoscale Convective Vortex Formation in a Weakly Sheared Moist Neutral Environment

2007 ◽  
Vol 64 (5) ◽  
pp. 1443-1466 ◽  
Author(s):  
Robert J. Conzemius ◽  
Richard W. Moore ◽  
Michael T. Montgomery ◽  
Christopher A. Davis
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Tangential Velocity ◽  
Lower Troposphere ◽  
Primary Objective ◽  
Vertical Shear ◽  
Convective System ◽  
Field Campaign ◽  
Mesoscale Convective ◽  
Mesoscale Convective Vortex

Abstract Idealized simulations of a diabatic Rossby vortex (DRV) in an initially moist neutral baroclinic environment are performed using the fifth-generation National Center for Atmospheric Research–Pennsylvania State University (NCAR–PSU) Mesoscale Model (MM5). The primary objective is to test the hypothesis that the formation and maintenance of midlatitude warm-season mesoscale convective vortices (MCVs) are largely influenced by balanced flow dynamics associated with a vortex that interacts with weak vertical shear. As a part of this objective, the simulated DRV is placed within the context of the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) field campaign by comparing its tangential velocity, radius of maximum winds, CAPE, and shear with the MCVs observed in BAMEX. The simulations reveal two distinct scales of development. At the larger scale, the most rapidly growing moist baroclinic mode is excited, and exponential growth of this mode occurs during the simulation. Embedded within the large-scale baroclinic wave is a convective system exhibiting the characteristic DRV development, with a positive potential vorticity (PV) anomaly in the lower troposphere and a negative PV anomaly in the upper troposphere, and the positive/negative PV doublet tilted downshear with height. The DRV warm-air advection mechanism is active, and the resulting deep convection helps to reinforce the DRV against the deleterious effects of environmental shear, causing an eastward motion of the convective system as a whole. The initial comparisons between the simulated DRVs and the BAMEX MCVs show that the simulated DRVs grew within background conditions of CAPE and shear similar to those observed for BAMEX MCVs and suggest that the same dynamical mechanisms are active. Because the BAMEX field campaign sampled MCVs in different backgrounds of CAPE and shear, the comparison also demonstrates the need to perform additional simulations to explore these different CAPE and shear regimes and to understand their impacts on the intensity and longevity of MCVs. Such a study has the additional benefit of placing MCV dynamics in an appropriate context for exploring their relevance to tropical cyclone formation.

scholarly journals A Subtropical Oceanic Mesoscale Convective Vortex Observed during SoWMEX/TiMREX

2011 ◽  
Vol 139 (8) ◽  
pp. 2367-2385 ◽  
Author(s):  
Hsiao-Wei Lai ◽  
Christopher A. Davis ◽  
Ben Jong-Dao Jou
Keyword(s):  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Southwest Monsoon ◽  
Convective System ◽  
Vortex Center ◽  
Moist Convection ◽  
Low Level ◽  
Mesoscale Convective ◽  
Deep Moist Convection ◽  
Mesoscale Convective Vortex

AbstractThis study examines a subtropical oceanic mesoscale convective vortex (MCV) that occurred from 1800 UTC 4 June to 1200 UTC 6 June 2008 during intensive observing period (IOP) 6 of the Southwest Monsoon Experiment (SoWMEX) and the Terrain-influenced Monsoon Rainfall Experiment (TiMREX). A dissipating mesoscale convective system reorganized within a nearly barotropic vorticity strip, which formed as a southwesterly low-level jet developed to the south of subsiding easterly flow over the southern Taiwan Strait. A cyclonic circulation was revealed on the northern edge of the mesoscale rainband with a horizontal scale of 200 km. An inner subvortex, on a scale of 25–30 km with maximum shear vorticity of 3 × 10−3 s−1, was embedded in the stronger convection. The vortex-relative southerly flow helped create local potential instability favorable for downshear convection enhancement. Strong low-level convergence suggests that stretching occurred within the MCV. Higher θe air, associated with significant potential and conditional instability, and high reflectivity signatures near the vortex center suggest that deep moist convection was responsible for the vortex stretching. Dry rear inflow penetrated into the MCV and suppressed convection in the upshear direction. A mesolow was also roughly observed within the larger vortex. The presence of intense vertical wind shear in the higher troposphere limited the vortex vertical extent to about 6 km.

scholarly journals A mesoscale convective system trapped along the Spanish Mediterranean Coast

2006 ◽  
Vol 7 ◽  
pp. 153-156 ◽  
Author(s):  
J. M. Sánchez-Laulhé
Keyword(s):  
Convective Instability ◽  
Heavy Rainfall ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Precipitable Water ◽  
Mediterranean Coast ◽  
Convective System ◽  
Convective Storm ◽  
Low Level ◽  
Mesoscale Convective

Abstract. This paper describes the evolution of a mesoscale convective system (MCS) developed over the Alboran Sea on 7 February 2005, using surface, upper-air stations, radar and satellite observations, and also data from an operational numerical model. The system developed during the night as a small convective storm line in an environment with slight convective instability, low precipitable water and strong low-level vertical wind shear near coast. The linear MCS moved northwards reaching the Spanish coast. Then it remained trapped along the coast for more than twelve hours, following the coast more than five hundred kilometres. The MCS here described had a fundamental orographic character due to: (1) the generation of a low-level storm inflow parallel to the coast, formed by blocking of the onshore flow by coastal mountains and (2) the orientation of both the mesoscale ascent from the sea towards the coastal mountains and the midlevel rear inflow from the coastal mountains to the sea. The main motivation of this work was to obtain a better understanding of the mechanisms relevant to the formation of heavy rainfall episodes occurring at Spanish Mediterranean coast associated with this kind of stationary or slowly moving MCSs.

scholarly journals Evolution of Pre- and Postconvective Environmental Profiles from Mesoscale Convective Systems during PECAN

2019 ◽  
Vol 147 (7) ◽  
pp. 2329-2354 ◽  
Author(s):  
Stacey M. Hitchcock ◽  
Russ S. Schumacher ◽  
Gregory R. Herman ◽  
Michael C. Coniglio ◽  
Matthew D. Parker ◽  
...  
Keyword(s):  
Potential Temperature ◽  
Cold Pool ◽  
Temperature Perturbation ◽  
Convective System ◽  
Equivalent Potential Temperature ◽  
Wind Maximum ◽  
Low Level ◽  
Equivalent Potential ◽  
Mesoscale Convective ◽  
Low Levels

Abstract During the Plains Elevated Convection at Night (PECAN) field campaign, 15 mesoscale convective system (MCS) environments were sampled by an array of instruments including radiosondes launched by three mobile sounding teams. Additional soundings were collected by fixed and mobile PECAN integrated sounding array (PISA) groups for a number of cases. Cluster analysis of observed vertical profiles established three primary preconvective categories: 1) those with an elevated maximum in equivalent potential temperature below a layer of potential instability; 2) those that maintain a daytime-like planetary boundary layer (PBL) and nearly potentially neutral low levels, sometimes even well after sunset despite the existence of a southerly low-level wind maximum; and 3) those that are potentially neutral at low levels, but have very weak or no southerly low-level winds. Profiles of equivalent potential temperature in elevated instability cases tend to evolve rapidly in time, while cases in the potentially neutral categories do not. Analysis of composite Rapid Refresh (RAP) environments indicate greater moisture content and moisture advection in an elevated layer in the elevated instability cases than in their potentially neutral counterparts. Postconvective soundings demonstrate significantly more variability, but cold pools were observed in nearly every PECAN MCS case. Following convection, perturbations range between −1.9 and −9.1 K over depths between 150 m and 4.35 km, but stronger, deeper stable layers lead to structures where the largest cold pool temperature perturbation is observed above the surface.

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