scholarly journals Wave Disturbances and Their Role in the Maintenance, Structure, and Evolution of a Mesoscale Convection System

2019 ◽  
Vol 77 (1) ◽  
pp. 51-77 ◽  
Author(s):  
Shushi Zhang ◽  
David B. Parsons ◽  
Yuan Wang
Keyword(s):  
Great Plains ◽  
Wave Energy ◽  
Deep Convection ◽  
Inversion Layer ◽  
Mesoscale Convective System ◽  
Vertical Shear ◽  
Cold Pool ◽  
Convective System ◽  
Convective Initiation ◽  
Mesoscale Convective

Abstract This study investigates a nocturnal mesoscale convective system (MCS) observed during the Plains Elevated Convection At Night (PECAN) field campaign. A series of wavelike features were observed ahead of this MCS with extensive convective initiation (CI) taking place in the wake of one of these disturbances. Simulations with the WRF-ARW Model were utilized to understand the dynamics of these disturbances and their impact on the MCS. In these simulations, an “elevated bore” formed within an inversion layer aloft in response to the layer being lifted by air flowing up and over the cold pool. As the bore propagated ahead of the MCS, the lifting created an environment more conducive to deep convection allowing the MCS to discretely propagate due to CI in the bore’s wake. The Scorer parameter was somewhat favorable for trapping of this wave energy, although aspects of the environment evolved to be consistent with the expectations for an n = 2 mode deep tropospheric gravity wave. A bore within an inversion layer aloft is reminiscent of disturbances predicted by two-layer hydraulic theory, contrasting with recent studies that suggest bores are frequently initiated by the interaction between the flow within stable nocturnal boundary layer and convectively generated cold pools. Idealized simulations that expand upon this two-layer approach with orography and a well-mixed layer below the inversion suggest that elevated bores provide a possible mechanism for daytime squall lines to remove the capping inversion often found over the Great Plains, particularly in synoptically disturbed environments where vertical shear could create a favorable trapping of wave energy.

Convection-Permitting Simulations of the Environment Supporting Widespread Turbulence within the Upper-Level Outflow of a Mesoscale Convective System

2009 ◽  
Vol 137 (6) ◽  
pp. 1972-1990 ◽  
Author(s):  
Stanley B. Trier ◽  
Robert D. Sharman
Keyword(s):  
Deep Convection ◽  
Potential Temperature ◽  
Mesoscale Convective System ◽  
Forecast Model ◽  
Static Stability ◽  
Vertical Shear ◽  
Convective System ◽  
Mesoscale Convective ◽  
Northern Edge ◽  
Upper Level

Abstract Widespread moderate turbulence was recorded on three specially equipped commercial airline flights over northern Kansas near the northern edge of the extensive cirrus anvil of a nocturnal mesoscale convective system (MCS) on 17 June 2005. A noteworthy aspect of the turbulence was its location several hundred kilometers from the active deep convection (i.e., large reflectivity) regions of the MCS. Herein, the MCS life cycle and the turbulence environment in its upper-level outflow are studied using Rapid Update Cycle (RUC) analyses and cloud-permitting simulations with the Weather Research and Forecast Model (WRF). It is demonstrated that strong vertical shear beneath the MCS outflow jet is critical to providing an environment that could support dynamic (e.g., shearing type) instabilities conducive to turbulence. Comparison of a control simulation to one in which the temperature tendency due to latent heating was eliminated indicates that strong vertical shear and corresponding reductions in the local Richardson number (Ri) to ∼0.25 at the northern edge of the anvil were almost entirely a consequence of the MCS-induced westerly outflow jet. The large vertical shear is found to decrease Ri both directly, and by contributing to reductions in static stability near the northern anvil edge through differential advection of (equivalent) potential temperature gradients, which are in turn influenced by adiabatic cooling associated with the mesoscale updraft located upstream within the anvil. On the south side of the MCS, the vertical shear associated with easterly outflow was significantly offset by environmental westerly shear, which resulted in larger Ri and less widespread model turbulent kinetic energy (TKE) than at the northern anvil edge.

scholarly journals Effects of Under-Resolved Convective Dynamics on the Evolution of a Squall Line

2019 ◽  
Vol 148 (1) ◽  
pp. 289-311 ◽  
Author(s):  
Adam Varble ◽  
Hugh Morrison ◽  
Edward Zipser
Keyword(s):  
Early Stage ◽  
Deep Convection ◽  
Mesoscale Convective System ◽  
Squall Line ◽  
Cold Pool ◽  
Convective System ◽  
Stratiform Region ◽  
Mesoscale Convective ◽  
Upper Level ◽  
Resolution Simulation

Abstract Simulations of a squall line observed on 20 May 2011 during the Midlatitude Continental Convective Clouds Experiment (MC3E) using 750- and 250-m horizontal grid spacing are performed. The higher-resolution simulation has less upshear-tilted deep convection and a more elevated rear inflow jet than the coarser-resolution simulation in better agreement with radar observations. A stronger cold pool eventually develops in the 250-m run; however, the more elevated rear inflow counteracts the cold pool circulation to produce more upright convective cores relative to the 750-m run. The differing structure in the 750-m run produces excessive midlevel front-to-rear detrainment, reinforcing excessive latent cooling and rear inflow descent at the rear of the stratiform region in a positive feedback. The contrasting mesoscale circulations are connected to early stage deep convective draft differences in the two simulations. Convective downdraft condensate mass, latent cooling, and downward motion all increase with downdraft area similarly in both simulations. However, the 750-m run has a relatively greater number of wide and fewer narrow downdrafts than the 250-m run averaged to the same 750-m grid, a consequence of downdrafts being under-resolved in the 750-m run. Under-resolved downdrafts in the 750-m run are associated with under-resolved updrafts and transport mid–upper-level zonal momentum downward to low levels too efficiently in the early stage deep convection. These results imply that under-resolved convective drafts in simulations may vertically transport air too efficiently and too far vertically, potentially biasing buoyancy and momentum distributions that impact mesoscale convective system evolution.

scholarly journals Dominant processes of extreme rainfall-producing mesoscale convective system over southeastern Korea: 7 July 2009 case

2015 ◽  
Vol 3 (10) ◽  
pp. 6459-6489
Author(s):  
J.-H. Jeong ◽  
D.-I. Lee ◽  
C.-C. Wang ◽  
I.-S. Han
Keyword(s):  
Metropolitan Area ◽  
Heavy Rainfall ◽  
Deep Convection ◽  
Mesoscale Convective System ◽  
Extreme Rainfall ◽  
Cold Pool ◽  
Convective System ◽  
Frontal Surface ◽  
Mesoscale Convective ◽  
Outflow Boundary

Abstract. An extreme rainfall-producing mesoscale convective system (MCS) associated with the Changma front in southeastern Korea was investigated using observational data. This event recorded historic rainfall and led to devastating flash floods and landslides in the Busan metropolitan area on 7 July 2009. The aim of the present study is to analyze and better understand the synoptic and mesoscale environment, and the behavior of quasi-stationary MCS causing extreme rainfall. Synoptic and mesoscale analyses indicate that the MCS and heavy rainfall occurred association with a stationary front which resembled a warm front in structure. A strong southwesterly low-level jet (LLJ) transported warm and humid air and supplied the moisture toward the front, and the air rose upwards above the frontal surface. As the moist air was conditionally unstable, repeated upstream initiation of deep convection by back-building occurred at the coastline, while old cells moved downstream parallel to the convective line with training effect. Because the motion of convective cells nearly opposed the backward propagation, the system as a whole moved slowly. The back-building behavior was linked to the convectively produced cold pool and its outflow boundary, which played an essential role in the propagation and maintenance of the rainfall system. As a result, the quasi-stationary MCS caused a prolonged duration of heavy rainfall, leading to extreme rainfall over the Busan metropolitan area.

scholarly journals Multiscale Processes Enabling the Longevity and Daytime Persistence of a Nocturnal Mesoscale Convective System

2019 ◽  
Vol 147 (2) ◽  
pp. 733-761 ◽  
Author(s):  
Manda B. Chasteen ◽  
Steven E. Koch ◽  
David B. Parsons
Keyword(s):  
Great Plains ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Cold Pool ◽  
Convective System ◽  
Near Surface ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Unstable Environment

Abstract Nocturnal mesoscale convective systems (MCSs) frequently develop over the Great Plains in the presence of a nocturnal low-level jet (LLJ), which contributes to convective maintenance by providing a source of instability, convergence, and low-level vertical wind shear. Although these nocturnal MCSs often dissipate during the morning, many persist into the following afternoon despite the cessation of the LLJ with the onset of solar heating. The environmental factors enabling the postsunrise persistence of nocturnal convection are currently not well understood. A thorough investigation into the processes supporting the longevity and daytime persistence of an MCS was conducted using routine observations, RAP analyses, and a WRF-ARW simulation. Elevated nocturnal convection developed in response to enhanced frontogenesis, which quickly grew upscale into a severe quasi-linear convective system (QLCS). The western portion of this QLCS reorganized into a bow echo with a pronounced cold pool and ultimately an organized leading-line, trailing-stratiform MCS as it moved into an increasingly unstable environment. Differential advection resulting from the interaction of the nocturnal LLJ with the topography of west Texas established considerable heterogeneity in moisture, CAPE, and CIN, which influenced the structure and evolution of the MCS. An inland-advected moisture plume significantly increased near-surface CAPE during the nighttime over central Texas, while the environment over southeastern Texas abruptly destabilized following the commencement of surface heating and downward moisture transport. The unique topography of the southern plains and the close proximity to the Gulf of Mexico provided an environment conducive to the postsunrise persistence of the organized MCS.

scholarly journals Numerical Simulation of Radial Cloud Bands within the Upper-Level Outflow of an Observed Mesoscale Convective System

2010 ◽  
Vol 67 (9) ◽  
pp. 2990-2999 ◽  
Author(s):  
S. B. Trier ◽  
R. D. Sharman ◽  
R. G. Fovell ◽  
R. G. Frehlich
Keyword(s):  
Deep Convection ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Static Stability ◽  
Vertical Shear ◽  
Convective System ◽  
Shallow Convection ◽  
Band Formation ◽  
Mesoscale Convective ◽  
Radial Outflow

Abstract Turbulence affecting aircraft is frequently reported within bands of cirrus anvil cloud extending radially outward from upstream deep convection in mesoscale convective systems (MCSs). A high-resolution convection permitting model is used to simulate bands of this type observed on 17 June 2005. The timing, location, and orientation of these simulated bands are similar to those in satellite imagery for this case. The 10–20-km horizontal spacing between the bands is also similar to typical spacing found in a recent satellite-based climatology of MCS-induced radial outflow bands. The simulated bands result from shallow convection in the near-neutral to weakly unstable MCS outer anvil. The weak stratification of the anvil, the ratio of band horizontal wavelength to the depth of the near-neutral anvil layer (5:1 to 10:1), and band orientation approximately parallel to the vertical shear within the same layer are similar to corresponding aspects of horizontal convective rolls in the atmospheric boundary layer, which result from thermal instability. The vertical shear in the MCS outflow is important not only in influencing the orientation of the radial bands but also for its role, through differential temperature advection, in helping to thermodynamically destabilize the environment in which they originate. High-frequency gravity waves emanating from the parent deep convection are trapped in a layer of strong static stability and vertical wind shear beneath the near-neutral anvil and, consistent with satellite studies, are oriented approximately normal to the developing radial bands. The wave-generated vertical displacements near the anvil base may aid band formation in the layer above.

scholarly journals Characteristics of mesoscale-convective-system-produced extreme rainfall over southeastern South Korea: 7 July 2009

2016 ◽  
Vol 16 (4) ◽  
pp. 927-939 ◽  
Author(s):  
Jong-Hoon Jeong ◽  
Dong-In Lee ◽  
Chung-Chieh Wang ◽  
In-Seong Han
Keyword(s):  
South Korea ◽  
Metropolitan Area ◽  
Heavy Rainfall ◽  
Deep Convection ◽  
Mesoscale Convective System ◽  
Extreme Rainfall ◽  
Cold Pool ◽  
Convective System ◽  
Frontal Surface ◽  
Mesoscale Convective

Abstract. An extreme-rainfall-producing mesoscale convective system (MCS) associated with the Changma front in southeastern South Korea was investigated using observational data. This event recorded historic rainfall and led to devastating flash floods and landslides in the Busan metropolitan area on 7 July 2009. The aim of the present study is to analyse the influences for the synoptic and mesoscale environment, and the reasons that the quasi-stationary MCS causes extreme rainfall. Synoptic and mesoscale analyses indicate that the MCS and heavy rainfall occurred in association with a stationary front which resembled a warm front in structure. A strong southwesterly low-level jet (LLJ) transported warm and humid air and supplied the moisture toward the front, and the air rose upwards above the frontal surface. As the moist air was conditionally unstable, repeated upstream initiation of deep convection by back-building occurred at the coastline, while old cells moved downstream parallel to the convective line with training effect. Because the motion of convective cells nearly opposed the backward propagation, the system as a whole moved slowly. The back-building behaviour was linked to the convectively generated cold pool and its outflow boundary, which played a role in the propagation and maintenance of the rainfall system. As a result, the quasi-stationary MCS caused a prolonged duration of heavy rainfall, leading to extreme rainfall over the Busan metropolitan area.

The Analysis and Prediction of Microphysical States and Polarimetric Radar Variables in a Mesoscale Convective System Using Double-Moment Microphysics, Multinetwork Radar Data, and the Ensemble Kalman Filter

2014 ◽  
Vol 142 (1) ◽  
pp. 141-162 ◽  
Author(s):  
Bryan J. Putnam ◽  
Ming Xue ◽  
Youngsun Jung ◽  
Nathan Snook ◽  
Guifu Zhang
Keyword(s):  
Kalman Filter ◽  
Ensemble Kalman Filter ◽  
Mesoscale Convective System ◽  
Radar Data ◽  
Cold Pool ◽  
Convective System ◽  
Polarimetric Radar ◽  
Microphysics Scheme ◽  
Mesoscale Convective ◽  
Double Moment

Abstract Doppler radar data are assimilated with an ensemble Kalman Filter (EnKF) in combination with a double-moment (DM) microphysics scheme in order to improve the analysis and forecast of microphysical states and precipitation structures within a mesoscale convective system (MCS) that passed over western Oklahoma on 8–9 May 2007. Reflectivity and radial velocity data from five operational Weather Surveillance Radar-1988 Doppler (WSR-88D) S-band radars as well as four experimental Collaborative and Adaptive Sensing of the Atmosphere (CASA) X-band radars are assimilated over a 1-h period using either single-moment (SM) or DM microphysics schemes within the forecast ensemble. Three-hour deterministic forecasts are initialized from the final ensemble mean analyses using a SM or DM scheme, respectively. Polarimetric radar variables are simulated from the analyses and compared with polarimetric WSR-88D observations for verification. EnKF assimilation of radar data using a multimoment microphysics scheme for an MCS case has not previously been documented in the literature. The use of DM microphysics during data assimilation improves simulated polarimetric variables through differentiation of particle size distributions (PSDs) within the stratiform and convective regions. The DM forecast initiated from the DM analysis shows significant qualitative improvement over the assimilation and forecast using SM microphysics in terms of the location and structure of the MCS precipitation. Quantitative precipitation forecasting skills are also improved in the DM forecast. Better handling of the PSDs by the DM scheme is believed to be responsible for the improved prediction of the surface cold pool, a stronger leading convective line, and improved areal extent of stratiform precipitation.

scholarly journals Warm-Core Formation in Tropical Storm Humberto (2001)

2012 ◽  
Vol 140 (4) ◽  
pp. 1177-1190 ◽  
Author(s):  
Klaus Dolling ◽  
Gary M. Barnes
Keyword(s):  
Energy Content ◽  
Early Stage ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Mesoscale Convective System ◽  
Tropical Storm ◽  
Central Pressure ◽  
Convective System ◽  
Warm Core ◽  
Mesoscale Convective

At 0600 UTC 22 September 2001, Humberto was a tropical depression with a minimum central pressure of 1010 hPa. Twelve hours later, when the first global positioning system dropwindsondes (GPS sondes) were jettisoned, Humberto’s minimum central pressure was 1000 hPa and it had attained tropical storm strength. Thirty GPS sondes, radar from the WP-3D, and in situ aircraft measurements are utilized to observe thermodynamic structures in Humberto and their relationship to stratiform and convective elements during the early stage of the formation of an eye. The analysis of Tropical Storm Humberto offers a new view of the pre-wind-induced surface heat exchange (pre-WISHE) stage of tropical cyclone evolution. Humberto contained a mesoscale convective vortex (MCV) similar to observations of other developing tropical systems. The MCV advects the exhaust from deep convection in the form of an anvil cyclonically over the low-level circulation center. On the trailing edge of the anvil an area of mesoscale descent induces dry adiabatic warming in the lower troposphere. The nascent warm core at low levels causes the initial drop in pressure at the surface and acts to cap the boundary layer (BL). As BL air flows into the nascent eye, the energy content increases until the energy is released from under the cap on the down shear side of the warm core in the form of vigorous cumulonimbi, which become the nascent eyewall. This series of events show one possible path in which a mesoscale convective system may evolve into a warm-cored structure and intensify into a hurricane.

scholarly journals Seven-Doppler Radar and In Situ Analysis of the 25–26 June 2015 Kansas MCS during PECAN

2019 ◽  
Vol 148 (1) ◽  
pp. 211-240 ◽  
Author(s):  
Rachel L. Miller ◽  
Conrad L. Ziegler ◽  
Michael I. Biggerstaff
Keyword(s):  
Doppler Radar ◽  
Mesoscale Convective System ◽  
Cold Pool ◽  
Convective System ◽  
Stable Layer ◽  
Kinematic Evolution ◽  
Stratiform Region ◽  
Stationary Front ◽  
Mesoscale Convective ◽  
Convective Cells

Abstract This case study analyzes a nocturnal mesoscale convective system (MCS) that was observed on 25–26 June 2015 in northeastern Kansas during the Plains Elevated Convection At Night (PECAN) project. Over the course of the observational period, a broken line of elevated nocturnal convective cells initiated around 0230 UTC on the cool side of a stationary front and subsequently merged to form a quasi-linear MCS that later developed strong, surface-based outflow and a trailing stratiform region. This study combines radar observations with mobile and fixed mesonet and sounding data taken during PECAN to analyze the kinematics and thermodynamics of the MCS from 0300 to 0630 UTC. This study is unique in that 38 consecutive multi-Doppler wind analyses are examined over the 3.5 h observation period, facilitating a long-duration analysis of the kinematic evolution of the nocturnal MCS. Radar analyses reveal that the initial convective cells and linear MCS are elevated and sustained by an elevated residual layer formed via weak ascent over the stationary front. During upscale growth, individual convective cells develop storm-scale cold pools due to pockets of descending rear-to-front flow that are measured by mobile mesonets. By 0500 UTC, kinematic analysis and mesonet observations show that the MCS has a surface-based cold pool and that convective line updrafts are ingesting parcels from below the stable layer. In this environment, the elevated system has become surface based since the cold pool lifting is sufficient for surface-based parcels to overcome the CIN associated with the frontal stable layer.

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