The impact of a mesoscale convective system cold pool on the northward propagation of the intertropical discontinuity over West Africa

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.

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

Monthly Weather Review ◽

10.1175/mwr-d-19-0187.1 ◽

2019 ◽

Vol 148 (1) ◽

pp. 289-311 ◽

Cited By ~ 2

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.

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

Monthly Weather Review ◽

10.1175/mwr-d-19-0151.1 ◽

2019 ◽

Vol 148 (1) ◽

pp. 211-240 ◽

Cited By ~ 2

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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Multiscale Characteristics and Evolution of Perturbations for Warm Season Convection-Allowing Precipitation Forecasts: Dependence on Background Flow and Method of Perturbation

Monthly Weather Review ◽

10.1175/mwr-d-13-00204.1 ◽

2014 ◽

Vol 142 (3) ◽

pp. 1053-1073 ◽

Cited By ~ 34

Author(s):

Aaron Johnson ◽

Xuguang Wang ◽

Ming Xue ◽

Fanyou Kong ◽

Gang Zhao ◽

...

Keyword(s):

Warm Season ◽

Mesoscale Convective System ◽

Haar Wavelet ◽

Precipitation Forecast ◽

Initial Time ◽

Small Scale ◽

Convective System ◽

Mesoscale Convective ◽

Perturbation Energy ◽

The Impact

Abstract Multiscale convection-allowing precipitation forecast perturbations are examined for two forecasts and systematically over 34 forecasts out to 30-h lead time using Haar Wavelet decomposition. Two small-scale initial condition (IC) perturbation methods are compared to the larger-scale IC and physics perturbations in an experimental convection-allowing ensemble. For a precipitation forecast driven primarily by a synoptic-scale baroclinic disturbance, small-scale IC perturbations resulted in little precipitation forecast perturbation energy on medium and large scales, compared to larger-scale IC and physics (LGPH) perturbations after the first few forecast hours. However, for a case where forecast convection at the initial time grew upscale into a mesoscale convective system (MCS), small-scale IC and LGPH perturbations resulted in similar forecast perturbation energy on all scales after about 12 h. Small-scale IC perturbations added to LGPH increased total forecast perturbation energy for this case. Averaged over 34 forecasts, the small-scale IC perturbations had little impact on large forecast scales while LGPH accounted for about half of the error energy on such scales. The impact of small-scale IC perturbations was also less than, but comparable to, the impact of LGPH perturbations on medium scales. On small scales, the impact of small-scale IC perturbations was at least as large as the LGPH perturbations. The spatial structure of small-scale IC perturbations affected the evolution of forecast perturbations, especially at medium scales. There was little systematic impact of the small-scale IC perturbations when added to LGPH. These results motivate further studies on properly sampling multiscale IC errors.

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The Impact of Low-Level Moisture Errors on Model Forecasts of an MCS Observed during PECAN

Monthly Weather Review ◽

10.1175/mwr-d-16-0296.1 ◽

2017 ◽

Vol 145 (9) ◽

pp. 3599-3624 ◽

Cited By ~ 17

Author(s):

John M. Peters ◽

Erik R. Nielsen ◽

Matthew D. Parker ◽

Stacey M. Hitchcock ◽

Russ S. Schumacher

Keyword(s):

Convective Available Potential Energy ◽

Mesoscale Convective System ◽

Squall Line ◽

Convective System ◽

Low Level ◽

Eastern Flank ◽

Western Flank ◽

Mesoscale Convective ◽

Outflow Boundary ◽

The Impact

This article investigates errors in forecasts of the environment near an elevated mesoscale convective system (MCS) in Iowa on 24–25 June 2015 during the Plains Elevated Convection at Night (PECAN) field campaign. The eastern flank of this MCS produced an outflow boundary (OFB) and moved southeastward along this OFB as a squall line. The western flank of the MCS remained quasi stationary approximately 100 km north of the system’s OFB and produced localized flooding. A total of 16 radiosondes were launched near the MCS’s eastern flank and 4 were launched near the MCS’s western flank. Convective available potential energy (CAPE) increased and convective inhibition (CIN) decreased substantially in observations during the 4 h prior to the arrival of the squall line. In contrast, the model analyses and forecasts substantially underpredicted CAPE and overpredicted CIN owing to their underrepresentation of moisture. Numerical simulations that placed the MCS at varying distances too far to the northeast were analyzed. MCS displacement error was strongly correlated with models’ underrepresentation of low-level moisture and their associated overrepresentation of the vertical distance between a parcel’s initial height and its level of free convection ([Formula: see text], which is correlated with CIN). The overpredicted [Formula: see text] in models resulted in air parcels requiring unrealistically far northeastward travel in a region of gradual meso- α-scale lift before these parcels initiated convection. These results suggest that erroneous MCS predictions by NWP models may sometimes result from poorly analyzed low-level moisture fields.

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Impact of vegetation changes on a mesoscale convective system in West Africa

Meteorology and Atmospheric Physics ◽

10.1007/s00703-010-0079-7 ◽

2010 ◽

Vol 107 (3-4) ◽

pp. 109-122 ◽

Cited By ~ 9

Author(s):

D. Lauwaet ◽

N. P. M. van Lipzig ◽

N. Kalthoff ◽

K. De Ridder

Keyword(s):

West Africa ◽

Mesoscale Convective System ◽

Convective System ◽

Vegetation Changes ◽

Mesoscale Convective

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Convergence zones and their impact on the initiation of a mesoscale convective system in West Africa

Quarterly Journal of the Royal Meteorological Society ◽

10.1002/qj.979 ◽

2011 ◽

Vol 138 (665) ◽

pp. 950-963 ◽

Cited By ~ 13

Author(s):

Vera Klüpfel ◽

Norbert Kalthoff ◽

Leonhard Gantner ◽

Christopher M. Taylor

Keyword(s):

West Africa ◽

Mesoscale Convective System ◽

Convective System ◽

Mesoscale Convective ◽

Convergence Zones

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Long-Lived Mesoscale Systems in a Low–Convective Inhibition Environment. Part II: Downshear Propagation

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-15-0074.1 ◽

2015 ◽

Vol 72 (11) ◽

pp. 4319-4336 ◽

Cited By ~ 9

Author(s):

Mitchell W. Moncrieff ◽

Todd P. Lane

Keyword(s):

Convective Available Potential Energy ◽

Mesoscale Convective System ◽

Cold Pool ◽

Convective System ◽

Mesoscale Circulation ◽

Secondary Importance ◽

Convective Systems ◽

Stratiform Region ◽

Mesoscale System ◽

Mesoscale Convective

Abstract Part II of this study of long-lived convective systems in a tropical environment focuses on forward-tilted, downshear-propagating systems that emerge spontaneously from idealized numerical simulations. These systems differ in important ways from the standard mesoscale convective system that is characterized by a rearward-tilted circulation with a trailing stratiform region, an overturning updraft, and a mesoscale downdraft. In contrast to this standard mesoscale system, the downshear-propagating system considered here does not feature a mesoscale downdraft and, although there is a cold pool it is of secondary importance to the propagation and maintenance of the system. The mesoscale downdraft is replaced by hydraulic-jump-like ascent beneath an elevated, forward-tilted overturning updraft with negligible convective available potential energy. Therefore, the mesoscale circulation is sustained almost entirely by the work done by the horizontal pressure gradient and the kinetic energy available from environmental shear. This category of organization is examined by cloud-system-resolving simulations and approximated by a nonlinear archetypal model of the quasi-steady Lagrangian-mean mesoscale circulation.

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An Orography-Associated Extreme Rainfall Event during TiMREX: Initiation, Storm Evolution, and Maintenance

Monthly Weather Review ◽

10.1175/mwr-d-11-00208.1 ◽

2012 ◽

Vol 140 (8) ◽

pp. 2555-2574 ◽

Cited By ~ 62

Author(s):

Weixin Xu ◽

Edward J. Zipser ◽

Yi-Leng Chen ◽

Chuntao Liu ◽

Yu-Chieng Liou ◽

...

Keyword(s):

Mesoscale Convective System ◽

Extreme Rainfall ◽

Cold Pool ◽

Convective System ◽

Extreme Rainfall Event ◽

Long Duration ◽

Mesoscale System ◽

Mesoscale Convective ◽

Storm Evolution ◽

Temperature Depression

Abstract This study investigates a long-duration mesoscale system with extremely heavy rainfall over southwest Taiwan during the Terrain-influenced Monsoon Rainfall Experiment (TiMREX). This mesoscale convective system develops offshore and stays quasi-stationary over the upstream ocean and southwest coast of Taiwan. New convection keeps developing upstream offshore but decays or dies after moving into the island, dropping the heaviest rain over the upstream ocean and coastal regions. Warm, moist, unstable conditions and a low-level jet (LLJ) are found only over the upstream ocean, while the island of Taiwan is under the control of a weak cold pool. The LLJ is lifted upward at the boundary between the cold pool and LLJ. Most convective clusters supporting the long-lived rainy mesoscale system are initiated and develop along that boundary. The initiation and maintenance is thought to be a “back-building–quasi-stationary” process. The cold pool forms from previous persistent precipitation with a temperature depression of 2°–4°C in the lowest 500 m, while the high terrain in Taiwan is thought to trap the cold pool from spreading or moving. As a result, the orography of Taiwan is “extended” to the upstream ocean and plays an indirect effect on the long-duration mesoscale system.

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

Natural Hazards and Earth System Sciences Discussions ◽

10.5194/nhessd-3-6459-2015 ◽

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.

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