scholarly journals Sensitivity of a Bowing Mesoscale Convective System to Horizontal Grid Spacing in a Convection-Allowing Ensemble

Atmosphere ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 384
Author(s):  
John R. Lawson ◽  
William A. Gallus ◽  
Corey K. Potvin
Keyword(s):  
Mesoscale Convective System ◽  
Real Data ◽  
The United States ◽  
Convective System ◽  
Grid Spacing ◽  
Structure Amplitude ◽  
Cold Pools ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Horizontal Grid

The bow echo, a mesoscale convective system (MCS) responsible for much hail and wind damage across the United States, is associated with poor skill in convection-allowing numerical model forecasts. Given the decrease in convection-allowing grid spacings within many operational forecasting systems, we investigate the effect of finer resolution on the character of bowing-MCS development in a real-data numerical simulation. Two ensembles were generated: one with a single domain of 3-km horizontal grid spacing, and another nesting a 1-km domain with two-way feedback. Ensemble members were generated from their control member with a stochastic kinetic-energy backscatter scheme, with identical initial and lateral-boundary conditions. Results suggest that resolution reduces hindcast skill of this MCS, as measured with an adaptation of the object-based Structure–Amplitude–Location method. The nested 1-km ensemble produces a faster system than in both the 3-km ensemble and observations. The nested 1-km simulation also produced stronger cold pools, which could be enhanced by the increased (fractal) cloud surface area with higher resolution, allowing more entrainment of dry air and hence increased evaporative cooling.

scholarly journals Toward 1-km Ensemble Forecasts over Large Domains

2017 ◽  
Vol 145 (8) ◽  
pp. 2943-2969 ◽  
Author(s):  
Craig S. Schwartz ◽  
Glen S. Romine ◽  
Kathryn R. Fossell ◽  
Ryan A. Sobash ◽  
Morris L. Weisman
Keyword(s):  
The United States ◽  
Grid Spacing ◽  
Ensemble Forecasts ◽  
Convective Systems ◽  
Object Based ◽  
Probabilistic Forecasts ◽  
Mesoscale Convective ◽  
Computational Resources ◽  
Horizontal Grid ◽  
Better Than

Precipitation forecasts from convection-allowing ensembles with 3- and 1-km horizontal grid spacing were evaluated between 15 May and 15 June 2013 over central and eastern portions of the United States. Probabilistic forecasts produced from 10- and 30-member, 3-km ensembles were consistently better than forecasts from individual 1-km ensemble members. However, 10-member, 1-km probabilistic forecasts usually were best, especially over the first 12 h and at rainfall rates ≥ 5.0 mm h−1 at later times. Further object-based investigation revealed that better 1-km forecasts at heavier rainfall rates were associated with more accurate placement of mesoscale convective systems compared to 3-km forecasts. The collective results indicate promise for 1-km ensembles once computational resources can support their operational implementation.

Subkilometer Simulation of a Torrential-Rain-Producing Mesoscale Convective System in East China. Part I: Model Verification and Convective Organization

2012 ◽  
Vol 140 (1) ◽  
pp. 184-201 ◽  
Author(s):  
Man Zhang ◽  
Da-Lin Zhang
Keyword(s):  
Model Simulation ◽  
Mesoscale Convective System ◽  
Model Verification ◽  
East China ◽  
Convective System ◽  
Grid Spacing ◽  
Torrential Rain ◽  
Stratiform Region ◽  
Mesoscale Convective ◽  
Torrential Rainfall

Abstract A nocturnal torrential-rain-producing mesoscale convective system (MCS) occurring during the mei-yu season of July 2003 in east China is studied using conventional observations, surface mesoanalysis, satellite and radar data, and a 24-h multinested model simulation with the finest grid spacing of 444 m. Observational analyses reveal the presence of several larger-scale conditions that were favorable for the development of the MCS, including mei-yu frontal lifting, moderate cold advection aloft and a moist monsoonal flow below, and an elongated old cold dome left behind by a previously dissipated MCS. Results show that the model could reproduce the evolution of the dissipating MCS and its associated cold outflows, the triggering of three separate convective storms over the remnant cold dome and the subsequent organization into a large MCS, and the convective generation of an intense surface meso-high and meso-β-scale radar reflectivity morphologies. In particular, the model reproduces the passage of several heavy-rain-producing convective bands at the leading convective line and the trailing stratiform region, leading to the torrential rainfall at nearly the right location. However, many of the above features are poorly simulated or missed when the finest model grid uses either 1.33- or 4-km grid spacing. Results indicate the important roles of isentropic lifting of moist monsoonal air over the cold dome in triggering deep convection, a low-level jet within an elevated moist layer in maintaining conditional instability, and the repeated formation and movement of convective cells along the same path in producing the torrential rainfall.

Tornadogenesis in a Simulated Mesovortex within a Mesoscale Convective System

2012 ◽  
Vol 69 (11) ◽  
pp. 3372-3390 ◽  
Author(s):  
Alexander D. Schenkman ◽  
Ming Xue ◽  
Alan Shapiro
Keyword(s):  
Three Dimensional ◽  
Mesoscale Convective System ◽  
Surface Friction ◽  
Convective System ◽  
Grid Spacing ◽  
Near Surface ◽  
Advanced Regional Prediction System ◽  
Low Level ◽  
Regional Prediction ◽  
Mesoscale Convective

Abstract The Advanced Regional Prediction System (ARPS) is used to simulate a tornadic mesovortex with the aim of understanding the associated tornadogenesis processes. The mesovortex was one of two tornadic mesovortices spawned by a mesoscale convective system (MCS) that traversed southwestern and central Oklahoma on 8–9 May 2007. The simulation used 100-m horizontal grid spacing, and is nested within two outer grids with 400-m and 2-km grid spacing, respectively. Both outer grids assimilate radar, upper-air, and surface observations via 5-min three-dimensional variational data assimilation (3DVAR) cycles. The 100-m grid is initialized from a 40-min forecast on the 400-m grid. Results from the 100-m simulation provide a detailed picture of the development of a mesovortex that produces a submesovortex-scale tornado-like vortex (TLV). Closer examination of the genesis of the TLV suggests that a strong low-level updraft is critical in converging and amplifying vertical vorticity associated with the mesovortex. Vertical cross sections and backward trajectory analyses from this low-level updraft reveal that the updraft is the upward branch of a strong rotor that forms just northwest of the simulated TLV. The horizontal vorticity in this rotor originates in the near-surface inflow and is caused by surface friction. An additional simulation with surface friction turned off does not produce a rotor, strong low-level updraft, or TLV. Comparison with previous two-dimensional numerical studies of rotors in the lee of mountains shows striking similarities to the rotor formation presented herein. The findings of this study are summarized in a four-stage conceptual model for tornadogenesis in this case that describes the evolution of the event from mesovortexgenesis through rotor development and finally TLV genesis and intensification.

scholarly journals Serial Upstream-Propagating Mesoscale Convective System Events over Southeastern South America

2008 ◽  
Vol 136 (8) ◽  
pp. 3087-3105 ◽  
Author(s):  
Vagner Anabor ◽  
David J. Stensrud ◽  
Osvaldo L. L. de Moraes
Keyword(s):  
South America ◽  
Convective Available Potential Energy ◽  
Mesoscale Convective System ◽  
The United States ◽  
Convective System ◽  
Pressure System ◽  
Low Level ◽  
The North ◽  
Synoptic Conditions ◽  
Mesoscale Convective

Abstract Serial mesoscale convective system (MCS) events with lifetimes over 18 h and up to nearly 70 h are routinely observed over southeastern South America from infrared satellite imagery during the spring and summer. These events begin over the southern La Plata River basin, with individual convective systems generally moving eastward with the cloud-layer-mean wind. However, an important and common subset of these serial MCS events shows individual MCSs moving to the east or southeast, yet the region of convective development as a whole shifts upstream to the north or northwest. Analyses of the composite mean environments from 10 of these upstream-propagating serial MCS events using NCEP–NCAR reanalysis data events indicates that the synoptic conditions resemble those found in mesoscale convective complex environments over the United States. The serial MCS events form within an environment of strong low-level warm advection and strong moisture advection between the surface and 700 hPa from the Amazon region southward. One feature that appears to particularly influence the low-level flow pattern at early times is a strong surface anticyclone located just off the coast of Brazil. At upper levels, the MCSs develop on the anticyclonic side of the entrance region to an upper-level jet. Mean soundings show that the atmosphere is moist from the surface to near 500 hPa, with values of convective available potential energy above 1200 J kg−1 at the time of system initiation. System dissipation and continued upstream propagation to the north and northwest occurs in tandem with a surface high pressure system that crosses the Andes Mountains from the west.

scholarly journals Diurnal Variation of TRMM/LIS Lightning Flash Radiances

2017 ◽  
Vol 98 (7) ◽  
pp. 1453-1470 ◽  
Author(s):  
Themistoklis Chronis ◽  
William J. Koshak
Keyword(s):  
Diurnal Variation ◽  
Mesoscale Convective System ◽  
Tropical Rainfall Measuring Mission ◽  
The United States ◽  
Global Scale ◽  
Diurnal Variations ◽  
Convective System ◽  
Lightning Flash ◽  
Mesoscale Convective ◽  
Imaging Sensor

Abstract This study provides, for the first time, an analysis of the climatological diurnal variations in the lightning flash radiance data product ε from the Tropical Rainfall Measuring Mission Lightning Imaging Sensor (TRMM/LIS). The ε values over 13 years (2002–14), and over a global scale (∼38°S–38°N), reveal novel and remarkably consistent regional and seasonal patterns as a function of the local solar time (LST). In particular, the diurnal variation of ε (over both continental and oceanic regions) is characterized by a monotonic increase from late afternoon (∼2000 LST), attaining a maximum around 0900 LST, followed by a decreasing trend. The continental (oceanic) ε values reach a broader minimum spanning from ∼1500 to 1900 LST (∼1800 to 2000). The relative diurnal amplitude variation in continental ε is about 45%, compared to about 15% for oceanic ε. This study confirms that the results are not affected by diurnal biases associated with instrument detection or other statistical artifacts. Notable agreement is shown between the diurnal variations of ε and the global-scale (∼38°S–38°N) mesoscale convective system areal extent. Comparisons with recently published diurnal variations of cloud-to-ground lightning peak current over the United States also exhibit a marked similarity. Given the novelty of these findings, a few tentative hypotheses about the underlying physical mechanism(s) are discussed.

scholarly journals Spatiotemporal Evolution of the Microphysical and Thermodynamic Characteristics of the 20 June 2015 PECAN MCS

2020 ◽  
Vol 148 (4) ◽  
pp. 1363-1388 ◽  
Author(s):  
Daniel M. Stechman ◽  
Greg M. McFarquhar ◽  
Robert M. Rauber ◽  
Michael M. Bell ◽  
Brian F. Jewett ◽  
...  
Keyword(s):  
Doppler Radar ◽  
Thermodynamic Characteristics ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Array Probe ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Using Data ◽  
Mesoscale Convective Vortex ◽  
Inflow Jet

Abstract This study examines microphysical and thermodynamic characteristics of the 20 June 2015 mesoscale convective system (MCS) observed during the Plains Elevated Convection At Night (PECAN) experiment, specifically within the transition zone (TZ), enhanced stratiform rain region (ESR), anvil region, melting layer (ML), and the rear inflow jet (RIJ). Analyses are developed from airborne optical array probe data and multiple-Doppler wind and reflectivity syntheses using data from the airborne NOAA Tail Doppler Radar (TDR) and ground-based Weather Surveillance Radar-1988 Doppler (WSR-88D) radars. Seven spiral ascents/descents of the NOAA P-3 aircraft were executed within various regions of the 20 June MCS. Aggregation modified by sublimation was observed in each MCS region, regardless of whether the sampling was within the RIJ. Sustained sublimation and evaporation of precipitation in subsaturated layers led to a trend of downward moistening across the ESR spirals, with greater degrees of subsaturation maintained when in the vicinity of the descending RIJ. In all cases where melting was observed, the ML acted as a prominent thermodynamic boundary, with differing rates of change in temperature and relative humidity above and below the ML. Two spiral profiles coincident with the rear inflow notch provided unique observations within the TZ and were interpreted in the context of similar observations from the 29 June 2003 Bow Echo and Mesoscale Convective Vortex Experiment MCS. There, sublimation cooling and enhanced descent within the RIJ allowed ice particles to survive to temperatures as warm as +6.8°C before completely sublimating/evaporating.

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

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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