scholarly journals Kinematic Observations of Misocyclones along Boundaries during IHOP

2007 ◽  
Vol 135 (5) ◽  
pp. 1749-1768 ◽  
Author(s):  
James N. Marquis ◽  
Yvette P. Richardson ◽  
Joshua M. Wurman
Keyword(s):  
Numerical Models ◽  
Cellular Structures ◽  
Moist Convection ◽  
Important Process ◽  
Vorticity Field ◽  
High Resolution Data ◽  
Air Masses ◽  
Low Level ◽  
Planetary Boundary Layers ◽  
Deep Moist Convection

Abstract During the International H2O Project, mobile radars collected high-resolution data of several 0.5–2-km-wide vertically oriented vortices (or misocyclones) along at least five mesoscale airmass boundaries. This study analyzes the properties of the misocyclones in three of these datasets—3, 10, and 19 June 2002—to verify findings from finescale numerical models and other past observations of misocyclones and to further the understanding of the role that they play in the initiation of deep moist convection and nonsupercell tornadoes. Misocyclones inflect or disjoint the swath of low-level convergence along each boundary to varying degrees depending on the size of their circulations. When several relatively large misocyclones are next to each other, the shape of low-level convergence along each boundary is arranged into a staircase pattern. Mergers of misocyclones are an important process in the evolution of the vorticity field, as a population of small vortices consolidates into a smaller number of larger ones. Additionally, merging misocyclones may affect the mixing of thermodynamic fields in their vicinity when the merger axis is perpendicular to the boundary. Misocyclones interact with linear and cellular structures in the planetary boundary layers (PBLs) of the air masses adjacent to each boundary. Cyclonic low-level vertical vorticity generated by both types of structures makes contact with each boundary and sometimes is incorporated into preexisting misocyclones. Intersections of either type of PBL structure with the boundary result in strengthened pockets of low-level convergence and, typically, strengthened misocyclones.

Quasi-idealized numerical simulations of processes involved in orogenic convection initiation over the Sierras de Córdoba mountains

2021 ◽  
Author(s):  
Christopher A. Davis
Keyword(s):  
Numerical Simulations ◽  
Mountain Range ◽  
Moist Convection ◽  
Low Level ◽  
Physical Mechanisms ◽  
Convergence Line ◽  
Synoptic Conditions ◽  
Deep Moist Convection ◽  
Outflow Boundary ◽  
Convection Initiation

Abstract The Sierras de Córdoba (SDC) mountain range in Argentina is a hotspot of deep moist convection initiation (CI). Radar climatology indicates that 44% of daytime CI events that occur near the SDC in spring and summer seasons and that are not associated with the passage of a cold front or an outflow boundary involve a northerly LLJ, and these events tend to preferentially occur over the southeast quadrant of the main ridge of the SDC. To investigate the physical mechanisms acting to cause CI, idealized convection-permitting numerical simulations with a horizontal grid spacing of 1 km were conducted using CM1. The sounding used for initializing the model featured a strong northerly LLJ, with synoptic conditions resembling those in a previously postulated conceptual model of CI over the region, making it a canonical case study. Differential heating of the mountain caused by solar insolation in conjunction with the low-level northerly flow sets up a convergence line on the eastern slopes of the SDC. The southern portion of this line experiences significant reduction in convective inhibition, and CI occurs over the SDC southeast quadrant. Thesimulated storm soon acquires supercellular characteristics, as observed. Additional simulations with varying LLJ strength also show CI over the southeast quadrant. A simulation without background flow generated convergence over the ridgeline, with widespread CI across the entire ridgeline. A simulation with mid- and upper-tropospheric westerlies removed indicates that CI is minimally influenced by gravity waves. We conclude that the low-level jet is sufficient to focus convection initiation over the southeast quadrant of the ridge.

Evaluating the conservation of energy variables in simulations of deep moist convection

2021 ◽  
Author(s):  
John M. Peters ◽  
Daniel R. Chavas
Keyword(s):  
Heat Capacity ◽  
Numerical Models ◽  
Deep Convection ◽  
Squall Line ◽  
Moist Convection ◽  
Conservation Of Energy ◽  
Deep Moist Convection ◽  
Static Energy ◽  
Hydrostatic Balance ◽  
Latent Heats

AbstractIt is often assumed in parcel theory calculations, numerical models, and cumulus parameterizations that moist static energy (MSE) is adiabatically conserved. However, the adiabatic conservation of MSE is only approximate because of the assumption of hydrostatic balance. Two alternative variables are evaluated here: MSE −IB and MSE +KE, wherein IB is the path integral of buoyancy (B) and KE is kinetic energy. Both of these variables relax the hydrostatic assumption and are more precisely conserved than MSE. This article quantifies the errors that result from assuming that the aforementioned variables are conserved in large eddy simulations (LES) of both disorganized and organized deep convection. Results show that both MSE −IB and MSE +KE better predict quantities along trajectories than MSE alone. MSE −IB is better conserved in isolated deep convection, whereas MSE −IB and MSE +KE perform comparably in squall line simulations. These results are explained by differences between the pressure perturbation behavior of squall lines and isolated convection. Errors in updraft B diagnoses are universally minimized when MSE−IB is assumed to be adiabatically conserved, but only when moisture dependencies of heat capacity and temperature dependency of latent heating are accounted for. When less accurate latent heat and heat capacity formulae were used, MSE−IB yielded poorer B predictions than MSE due to compensating errors. Our results suggest that various applications would benefit from using either MSE −IB or MSE +KE instead of MSE with properly formulated heat capacities and latent heats.

scholarly journals Image Processing of Radar Mosaics for the Climatology of Convection Initiation in South China

2020 ◽  
Vol 59 (1) ◽  
pp. 65-81 ◽  
Author(s):  
Lanqiang Bai ◽  
Guixing Chen ◽  
Ling Huang
Keyword(s):  
South China ◽  
Numerical Models ◽  
Early Morning ◽  
Moist Convection ◽  
Late Night ◽  
Morning Peak ◽  
Spatial Modes ◽  
Triggering Mechanisms ◽  
Deep Moist Convection ◽  
Convection Initiation

AbstractA dataset of convection initiation (CI) is of great value in studying the triggering mechanisms of deep moist convection and evaluating the performances of numerical models. In recent years, the data quality of the operationally generated radar mosaics over China has been greatly improved, which provides an opportunity to retrieve a CI dataset from that region. In this work, an attempt is made to reveal the potential of applying a simple framework of objective CI detection for the study of CI climatology in China. The framework was tested using radar mosaic maps in South China that were accessible online. The identified CI events were validated in both direct and indirect ways. On the basis of a direct manual check, nearly all of the identified CI cells had an organized motion. The precipitation echoes of the cells had a median duration of approximately 2.5 h. The CI occurrences were further compared with rainfall estimates to ensure physical consistency. The diurnal cycle of CI occurrence exhibits three major modes: a late-night-to-morning peak at the windward coasts and offshore, a noon-to-late-afternoon peak on the coastal land, and an evening-to-early-morning peak over the northwestern highland. These spatial modes agree well with those of rainfall, indirectly suggesting the reliability of the CI statistics. By processing radar mosaic maps, such a framework could be applied for studying CI climatology over China and other regions.

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.

A Lagrangian Perspective on Parameterizing Deep Convection

2019 ◽  
Vol 147 (11) ◽  
pp. 4127-4149 ◽  
Author(s):  
Ron McTaggart-Cowan ◽  
Paul A. Vaillancourt ◽  
Ayrton Zadra ◽  
Leo Separovic ◽  
Shawn Corvec ◽  
...  
Keyword(s):  
Numerical Models ◽  
Spatial Scales ◽  
Deep Convection ◽  
Convective Precipitation ◽  
Moist Convection ◽  
Gray Zone ◽  
Convective Initiation ◽  
Intermittent Behavior ◽  
Cloud Properties ◽  
Deep Moist Convection

Abstract The parameterization of deep moist convection as a subgrid-scale process in numerical models of the atmosphere is required at resolutions that extend well into the convective “gray zone,” the range of grid spacings over which such convection is partially resolved. However, as model resolution approaches the gray zone, the assumptions upon which most existing convective parameterizations are based begin to break down. We focus here on one aspect of this problem that emerges as the temporal and spatial scales of the model become similar to those of deep convection itself. The common practice of static tendency application over a prescribed adjustment period leads to logical inconsistencies at resolutions approaching the gray zone, while more frequent refreshment of the convective calculations can lead to undesirable intermittent behavior. A proposed parcel-based treatment of convective initiation introduces memory into the system in a manner that is consistent with the underlying physical principles of convective triggering, thus reducing the prevalence of unrealistic gradients in convective activity in an operational model running with a 10 km grid spacing. The subsequent introduction of a framework that considers convective clouds as persistent objects, each possessing unique attributes that describe physically relevant cloud properties, appears to improve convective precipitation patterns by depicting realistic cloud memory, movement, and decay. Combined, this Lagrangian view of convection addresses one aspect of the convective gray zone problem and lays a foundation for more realistic treatments of the convective life cycle in parameterization schemes.

scholarly journals A Five-Year Radar-Based Climatology of Tropopause Folds and Deep Convection over Wales, United Kingdom

2013 ◽  
Vol 141 (5) ◽  
pp. 1693-1707 ◽  
Author(s):  
Bogdan Antonescu ◽  
Geraint Vaughan ◽  
David M. Schultz
Keyword(s):  
United Kingdom ◽  
Deep Convection ◽  
Moist Convection ◽  
Isolated Cells ◽  
Very High Frequency ◽  
High Resolution Data ◽  
Convective Storms ◽  
Deep Moist Convection ◽  
Upper Level ◽  
Western Side

AbstractA five-year (2006–10) radar-based climatology of tropopause folds and convective storms was constructed for Wales, United Kingdom, to determine how deep, moist convection is modulated by tropopause folds. Based on the continuous, high-resolution data from a very high frequency (VHF) wind-profiling radar located at Capel Dewi, Wales, 183 tropopause folds were identified. Tropopause folds were most frequent in January with a secondary maximum in July. Based on data from the U.K. weather radar network, a climatology of 685 convective storms was developed. The occurrence of convective storms was relatively high year-round except for an abrupt minimum in February–April. Multicellular lines (43.5%) were the most common morphology with a maximum in October, followed by isolated cells (33.1%) with a maximum in May–September, and nonlinear clusters (23.4%) with a maximum in November–January. Convective storms were associated with 104 (56.8%) of the tropopause folds identified in this study, with the association strongest in December. Of the 55 tropopause folds observed on the eastern side of an upper-level trough, 37 (67.3%) were associated with convective storms, most commonly in the form of multicellular lines. Of the 128 tropopause folds observed on the western side of an upper-level trough, 42 (32.8%) were associated with convective storms, most commonly isolated cells. These results suggest that more organized storms tend to form in environments favorable for synoptic-scale ascent.

scholarly journals Environment Associated with Deep Moist Convection under SALLJ Conditions: A Case Study

2010 ◽  
Vol 25 (3) ◽  
pp. 970-984 ◽  
Author(s):  
Paloma Borque ◽  
Paola Salio ◽  
Matilde Nicolini ◽  
Yanina García Skabar
Keyword(s):  
Frontal Zone ◽  
Mesoscale Convective Systems ◽  
South American ◽  
Moist Convection ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Low Level Jet ◽  
Deep Moist Convection

Abstract The present work focuses on the study of the environmental conditions preceding the development of a group of subtropical mesoscale convective systems over central and northern Argentina on 6–7 February 2003 during the South American Low Level Jet Experiment. This period was characterized by an extreme northerly low-level flow along the eastern Andes foothills [South American low-level jet (SALLJ)]. The entire studied episode was dominated by the presence of a very unstable air mass over northern Argentina and a frontal zone near 40°S. The SALLJ generated an important destabilization of the atmosphere due to the strong humidity and differential temperature advection. Orography provided an extra lifting motion to the configuration of the regional wind field, which was efficient in forcing the initiation of convection. Once convection developed, it moved and regenerated in regions where the convective instability was horizontally homogeneous and stronger.

High Resolution HIRLAM Simulations of the Role of Low-Level Sea-Breeze Convergence in Initiating Deep Moist Convection in the Eastern Iberian Peninsula

2014 ◽  
Vol 154 (1) ◽  
pp. 81-100 ◽  
Author(s):  
Cesar Azorin-Molina ◽  
Sander Tijm ◽  
Elizabeth E. Ebert ◽  
Sergio-M. Vicente-Serrano ◽  
Maria-Jose Estrela
Keyword(s):  
High Resolution ◽  
Iberian Peninsula ◽  
Sea Breeze ◽  
Moist Convection ◽  
Low Level ◽  
Deep Moist Convection

Practical Predictability of the 20 May 2013 Tornadic Thunderstorm Event in Oklahoma: Sensitivity to Synoptic Timing and Topographical Influence

2015 ◽  
Vol 143 (8) ◽  
pp. 2973-2997 ◽  
Author(s):  
Yunji Zhang ◽  
Fuqing Zhang ◽  
David J. Stensrud ◽  
Zhiyong Meng
Keyword(s):  
Boundary Layer ◽  
Vertical Mixing ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Moist Convection ◽  
Atmospheric Conditions ◽  
Low Level ◽  
Deep Moist Convection ◽  
Simulation Time

Abstract The practical predictability of severe convective thunderstorms during the 20 May 2013 severe weather event that produced the catastrophic enhanced Fujita scale 5 (EF-5) tornado in Moore, Oklahoma, was explored using ensembles of convective-permitting model simulations. The sensitivity of initiation and the subsequent organization and intensity of the thunderstorms to small yet realistic uncertainties in boundary layer and topographical influence within a few hours preceding the thunderstorm event was examined. It was found that small shifts in either simulation time or terrain configuration led to considerable differences in the atmospheric conditions within the boundary layer. Small shifts in simulation time led to changes in low-level moisture and instability, primarily through the vertical distribution of moisture within the boundary layer due to vertical mixing during the diurnal cycle as well as advection by low-level jets, thereby influencing convection initiation. Small shifts in terrain led to changes in the wind field, low-level vertical wind shear, and storm-relative environmental helicity, altering locally enhanced convergence that may trigger convection. After initiation, an upscale growth of errors resulting from deep moist convection led to large forecast uncertainties in the timing, intensity, structure, and organization of the developing mesoscale convective system and its embedded supercells.

scholarly journals Low-level Mesoscale and Cloud-scale Interactions Promoting Deep Convection Initiation

2021 ◽  
Author(s):  
James N. Marquis ◽  
Adam C. Varble ◽  
Paul Robinson ◽  
T. Connor. Nelson ◽  
Katja Friedrich
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Surface Wind ◽  
Horizontal Wind ◽  
Moist Convection ◽  
Surface Precipitation ◽  
Low Level ◽  
Deep Moist Convection ◽  
Convection Initiation

AbstractData from scanning radars, radiosondes, and vertical profilers deployed during three field campaigns are analyzed to study interactions between cloud-scale updrafts associated with initiating deep moist convection and the surrounding environment. Three cases are analyzed in which the radar networks permitted dual-Doppler wind retrievals in clear air preceding and during the onset of surface precipitation. These observations capture the evolution of: i) the mesoscale and boundary layer flow, and ii) low-level updrafts associated with deep moist convection initiation (CI) events yielding sustained or short-lived precipitating storms.The elimination of convective inhibition did not distinguish between sustained and unsustained CI events, though the vertical distribution of convective available potential energy may have played a role. The clearest signal differentiating the initiation of sustained versus unsustained precipitating deep convection was the depth of the low-level horizontal wind convergence associated with the mesoscale flow feature triggering CI, a sharp surface wind shift boundary or orographic upslope flow. The depth of the boundary layer relative to the height of the LFC failed to be a consistent indicator of CI potential. Widths of the earliest detectable low-level updrafts associated with sustained precipitating deep convection were ~3-5 km, larger than updrafts associated with surrounding boundary layer turbulence (~1-3-km wide). It is hypothesized that updrafts of this larger size are important for initiating cells to survive the destructive effects of buoyancy dilution via entrainment.

Sign in / Sign up

Export Citation Format

Share Document