Urban and land surface effects on the 30 July 2003 mesoscale convective system event observed in the southern Great Plains

Abstract This study examines whether and how land–atmosphere interactions can have an impact on nocturnal convection over the southern Great Plains (SGP) through numerical simulations of an intense nocturnal mesoscale convective system (MCS) on 19–20 June 2007 with the Weather Research and Forecasting (WRF) Model. High-resolution nested simulations were conducted using realistic and idealized land surfaces and two planetary boundary layer (PBL) parameterizations (PBLp): Yonsei University (YSU) and Mellor–Yamada–Janjić (MYJ). Differences in timing and amount of MCS precipitation among observations and model results were examined in the light of daytime land–atmosphere interactions, nocturnal prestorm environment, and cold pool strength. At the meso-γ scale, land cover and soil type have as much of an effect on the simulated prestorm environment as the choice of PBLp: MYJ simulations exhibit strong sensitivity to changes in the land surface in contrast to negligible impact in the case of YSU. At the end of the afternoon, as the boundary layer collapses, a more homogeneous and deeper PBL (and stronger low-level shear) is evident for YSU as compared to MYJ when initial conditions and land surface properties are the same. At the meso-β scale, propagation speed is faster and organization (bow echo morphology) and cold pool strength are enhanced when nocturnal PBL heights are higher, and there is stronger low-level shear in the prestorm environment independent of the boundary layer parameterization for different land surface conditions. A comparison of one- and two-way nested MYJ results demonstrates how daytime land–atmosphere interactions modify the prestorm environment remotely through advection of low-level thermodynamic features. This remote feedback strongly impacts the MCS development phase as well as its spatial organization and propagation velocity and, consequently, nocturnal rainfall. These results indicate that synoptic- and meso-α-scale dynamics can play an important role in determining the spatial and temporal scales over which precipitation feedbacks of land–atmosphere interactions emerge regionally. Finally, this study demonstrates the high degree of uncertainty in defining the spatial and temporal scales of land–atmosphere interactions where and when organized convection is dominant.

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Climatology of Linear Mesoscale Convective System Morphology in the United States based on Random Forests Method

Journal of Climate ◽

10.1175/jcli-d-20-0862.1 ◽

2021 ◽

pp. 1-52

Author(s):

Wenjun Cui ◽

Xiquan Dong ◽

Baike Xi ◽

Zhe Feng

Keyword(s):

United States ◽

Great Plains ◽

Warm Season ◽

Mesoscale Convective System ◽

Propagation Speed ◽

Extreme Rainfall ◽

The United States ◽

Convective System ◽

Large Variability ◽

Mesoscale Convective

AbstractThis study uses machine learning methods, specifically the random forest (RF), on a radar-based mesoscale convective system (MCS) tracking dataset to classify the five types of linear MCS morphology in the contiguous United States during the period 2004-2016. The algorithm is trained using radar- and satellite-derived spatial and morphological parameters, and reanalysis environmental information from 5-yr manually identified nonlinear and five linear MCS modes. The algorithm is then used to automate the classification of linear MCSs over 8 years with high accuracy, providing a systematic, long-term climatology of linear MCSs. Results reveal that nearly 40% of MCSs are classified as linear MCSs, in which half of the linear events belong to the type of system having a leading convective line. The occurrence of linear MCSs shows large annual and seasonal variations. On average, 113 linear MCSs occur annually during the warm season (through March to October), with most of these events clustered from May through August in the central eastern Great Plains. MCS characteristics, including duration, propagation speed, orientation, and system cloud size, have large variability among the different linear modes. The systems having a trailing convective line and the systems having a back-building area of convection typically move more slowly and have higher precipitation rate, and thus have higher potential in producing extreme rainfall and flash flooding. Analysis of the environmental conditions associated with linear MCSs show that the storm-relative flow is of most importance in determining the organization mode of linear MCSs.

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

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0348.1 ◽

2019 ◽

Vol 77 (1) ◽

pp. 51-77 ◽

Cited By ~ 5

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.

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

Monthly Weather Review ◽

10.1175/mwr-d-18-0233.1 ◽

2019 ◽

Vol 147 (2) ◽

pp. 733-761 ◽

Cited By ~ 3

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.

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Nocturnal Convection Initiation during PECAN 2015

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-18-0299.1 ◽

2019 ◽

Vol 100 (11) ◽

pp. 2223-2239 ◽

Cited By ~ 10

Author(s):

Tammy M. Weckwerth ◽

John Hanesiak ◽

James W. Wilson ◽

Stanley B. Trier ◽

Samuel K. Degelia ◽

...

Keyword(s):

Great Plains ◽

Current Knowledge ◽

Wrf Model ◽

Mesoscale Convective System ◽

Convective System ◽

University Of Oklahoma ◽

Different Types ◽

Mesoscale Convective ◽

Convection Initiation ◽

The University

AbstractNocturnal convection initiation (NCI) is more difficult to anticipate and forecast than daytime convection initiation (CI). A major component of the Plains Elevated Convection at Night (PECAN) field campaign in the U.S. Great Plains was to intensively sample NCI and its near environment. In this article, we summarize NCI types observed during PECAN: 1 June–16 July 2015. These NCI types, classified using PECAN radar composites, are associated with 1) frontal overrunning, 2) the low-level jet (LLJ), 3) a preexisting mesoscale convective system (MCS), 4) a bore or density current, and 5) a nocturnal atmosphere lacking a clearly observed forcing mechanism (pristine). An example and description of each of these different types of PECAN NCI events are presented. The University of Oklahoma real-time 4-km Weather Research and Forecasting (WRF) Model ensemble forecast runs illustrate that the above categories having larger-scale organization (e.g., NCI associated with frontal overrunning and NCI near a preexisting MCS) were better forecasted than pristine. Based on current knowledge and data from PECAN, conceptual models summarizing key environmental features are presented and physical processes underlying the development of each of these different types of NCI events are discussed.

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Evaluation of Cumulus and Microphysics Parameterizations in WRF across the Convective Gray Zone

Weather and Forecasting ◽

10.1175/waf-d-18-0178.1 ◽

2019 ◽

Vol 34 (4) ◽

pp. 1097-1115 ◽

Cited By ~ 10

Author(s):

Julia Jeworrek ◽

Gregory West ◽

Roland Stull

Keyword(s):

Great Plains ◽

Wrf Model ◽

Mesoscale Convective System ◽

The United States ◽

Smooth Transition ◽

Cumulus Parameterization ◽

Convective System ◽

Gray Zone ◽

Cumulus Scheme ◽

Mesoscale Convective

Abstract This study evaluates the grid-length dependency of the Weather Research and Forecasting (WRF) Model precipitation performance for two cases in the Southern Great Plains of the United States. The aim is to investigate the ability of different cumulus and microphysics parameterization schemes to represent precipitation processes throughout the transition between parameterized and resolved convective scales (e.g., the gray zone). The cases include the following: 1) a mesoscale convective system causing intense local precipitation, and 2) a frontal passage with light but continuous rainfall. The choice of cumulus parameterization appears to be a crucial differentiator in convective development and resulting precipitation patterns in the WRF simulations. Different microphysics schemes produce very similar outcomes, yet some of the more sophisticated schemes have substantially longer run times. This suggests that this additional computational expense does not necessarily provide meaningful forecast improvements, and those looking to run such schemes should perform their own evaluation to determine if this expense is warranted for their application. The best performing cumulus scheme overall for the two cases studies here was the scale-aware Grell–Freitas cumulus scheme. It was able to reproduce a smooth transition from subgrid- (cumulus) to resolved-scale (microphysics) precipitation with increasing resolution. It also produced the smallest errors for the convective event, outperforming the other cumulus schemes in predicting the timing and intensity of the precipitation.

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Observed Evidence of Enhanced Probability of Mesoscale Convective System Initiations due to Land Surface Heterogeneity in Semiarid East Asia

SOLA ◽

10.2151/sola.2019-026 ◽

2019 ◽

Vol 15 (0) ◽

pp. 143-148

Author(s):

Hiroki Teramura ◽

Tomonori Sato ◽

Kenta Tamura

Keyword(s):

East Asia ◽

Land Surface ◽

Mesoscale Convective System ◽

Surface Heterogeneity ◽

Convective System ◽

Mesoscale Convective ◽

Land Surface Heterogeneity

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An Intercomparison of Simulated Rainfall and Evapotranspiration Associated with a Mesoscale Convective System over West Africa

Weather and Forecasting ◽

10.1175/2009waf2222250.1 ◽

2010 ◽

Vol 25 (1) ◽

pp. 37-60 ◽

Cited By ~ 19

Author(s):

Françoise Guichard ◽

Nicole Asencio ◽

Christophe Peugeot ◽

Olivier Bock ◽

Jean-Luc Redelsperger ◽

...

Keyword(s):

West Africa ◽

Land Surface ◽

Mesoscale Convective System ◽

Precipitable Water ◽

Horizontal Resolution ◽

Surface Energy Budget ◽

Convective System ◽

Land Surface Modeling ◽

Multidisciplinary Analysis ◽

Mesoscale Convective

Abstract An evaluation of precipitation and evapotranspiration simulated by mesoscale models is carried out within the African Monsoon Multidisciplinary Analysis (AMMA) program. Six models performed simulations of a mesoscale convective system (MCS) observed to cross part of West Africa in August 2005. Initial and boundary conditions are found to significantly control the locations of rainfall at synoptic scales as simulated with either mesoscale or global models. When initialized and forced at their boundaries by the same analysis, all models forecast a westward-moving rainfall structure, as observed by satellite products. However, rainfall is also forecast at other locations where none was observed, and the nighttime northward propagation of rainfall is not well reproduced. There is a wide spread in the rainfall rates across simulations, but also among satellite products. The range of simulated meridional fluctuations of evapotranspiration (E) appears reasonable, but E displays an overly strong zonal symmetry. Offline land surface modeling and surface energy budget considerations show that errors in the simulated E are not simply related to errors in the surface evaporative fraction, and involve the significant impact of cloud cover on the incoming surface shortwave flux. The use of higher horizontal resolution (a few km) enhances the variability of precipitation, evapotranspiration, and precipitable water (PW) at the mesoscale. It also leads to a weakening of the daytime precipitation, less evapotranspiration, and smaller PW amounts. The simulated MCS propagates farther northward and somewhat faster within an overall drier atmosphere. These changes are associated with a strengthening of the links between PW and precipitation.

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Ensemble Probabilistic Prediction of a Mesoscale Convective System and Associated Polarimetric Radar Variables Using Single-Moment and Double-Moment Microphysics Schemes and EnKF Radar Data Assimilation

Monthly Weather Review ◽

10.1175/mwr-d-16-0162.1 ◽

2017 ◽

Vol 145 (6) ◽

pp. 2257-2279 ◽

Cited By ~ 12

Author(s):

Bryan J. Putnam ◽

Ming Xue ◽

Youngsun Jung ◽

Nathan A. Snook ◽

Guifu Zhang

Keyword(s):

Mesoscale Convective System ◽

Radar Data ◽

Convective Precipitation ◽

Convective System ◽

Ensemble Forecasts ◽

Verification Methods ◽

Probabilistic Forecasts ◽

Mesoscale Convective ◽

Single Moment ◽

Double Moment

Abstract Ensemble-based probabilistic forecasts are performed for a mesoscale convective system (MCS) that occurred over Oklahoma on 8–9 May 2007, initialized from ensemble Kalman filter analyses using multinetwork radar data and different microphysics schemes. Two experiments are conducted, using either a single-moment or double-moment microphysics scheme during the 1-h-long assimilation period and in subsequent 3-h ensemble forecasts. Qualitative and quantitative verifications are performed on the ensemble forecasts, including probabilistic skill scores. The predicted dual-polarization (dual-pol) radar variables and their probabilistic forecasts are also evaluated against available dual-pol radar observations, and discussed in relation to predicted microphysical states and structures. Evaluation of predicted reflectivity (Z) fields shows that the double-moment ensemble predicts the precipitation coverage of the leading convective line and stratiform precipitation regions of the MCS with higher probabilities throughout the forecast period compared to the single-moment ensemble. In terms of the simulated differential reflectivity (ZDR) and specific differential phase (KDP) fields, the double-moment ensemble compares more realistically to the observations and better distinguishes the stratiform and convective precipitation regions. The ZDR from individual ensemble members indicates better raindrop size sorting along the leading convective line in the double-moment ensemble. Various commonly used ensemble forecast verification methods are examined for the prediction of dual-pol variables. The results demonstrate the challenges associated with verifying predicted dual-pol fields that can vary significantly in value over small distances. Several microphysics biases are noted with the help of simulated dual-pol variables, such as substantial overprediction of KDP values in the single-moment ensemble.

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