scholarly journals A High-Resolution Aerial Survey and Radar Analysis of Quasi-Linear Convective System Surface Vortex Damage Paths from 31 August 2014

2017 ◽  
Vol 32 (2) ◽  
pp. 441-467 ◽  
Author(s):  
Kevin D. Skow ◽  
Craig Cogil
Keyword(s):  
High Resolution ◽  
Aerial Photography ◽  
Agricultural Land ◽  
Leading Edge ◽  
Radar Data ◽  
Aerial Survey ◽  
Cold Pool ◽  
Convective System ◽  
Des Moines ◽  
Surface Vortex

Abstract On the evening of 31 August 2014, a powerful quasi-linear convective system (QLCS) impacted much of Iowa. In the weeks following the event, the entire path of the QLCS was imaged at ~1-m resolution using aerial photography through the National Agriculture Imagery Program. The predominantly flat, mature agricultural land cover of central Iowa provided an excellent medium on which to document wind phenomena of varying scales. The high-resolution aerial data, in combination with recent spatial, temporal, and polarimetric upgrades to the Weather Surveillance Radar-1988 Doppler (WSR-88D) network, offer an extraordinary glimpse into the quantity, evolution, and scale of surface vortices generated throughout the entire lifespan of this QLCS. One hundred eleven damage tracks associated with these vortices were cataloged along the storm’s 350-km path, ranging in length from 130 m to nearly 18 km. This study classified 35 of these circulations as tornadoes using a series of tests that weighed track characteristics and radar data. Unusual features, such as a likely tornado merger and multiple instances of tornadoes occluding behind the leading edge of the QLCS surface cold pool, are examined. Possible genesis mechanisms and National Weather Service operational implications are also discussed. A new, behavioral-based approach for identifying a tornadic debris signature (TDS) is presented that may be better suited for QLCS tornadoes. Twelve TDSs were cataloged on 31 August 2014 using this methodology at ranges up to 90 km from the Des Moines, Iowa, WSR-88D.

scholarly journals Origin and Maintenance of the Long-Lasting, Outer Mesoscale Convective System in Typhoon Fengshen (2008)

2014 ◽  
Vol 142 (8) ◽  
pp. 2838-2859 ◽  
Author(s):  
Buo-Fu Chen ◽  
Russell L. Elsberry ◽  
Cheng-Shang Lee
Keyword(s):  
Inner Core ◽  
Outer Region ◽  
Vertical Wind Shear ◽  
Leading Edge ◽  
Cold Pool ◽  
Convective System ◽  
Rain Area ◽  
Characteristic Structure ◽  
Low Level ◽  
Mesoscale Convective

Abstract Outer mesoscale convective systems (OMCSs) are long-lasting, heavy rainfall events separate from the inner-core rainfall that have previously been shown to occur in 22% of western North Pacific tropical cyclones (TCs). Environmental conditions accompanying the development of 62 OMCSs are contrasted with the conditions in TCs that do not include an OMCS. The development, kinematic structure, and maintenance mechanisms of an OMCS that occurred to the southwest of Typhoon Fengshen (2008) are studied with Weather Research and Forecasting Model simulations. Quick Scatterometer (QuikSCAT) observations and the simulations indicate the low-level TC circulation was deflected around the Luzon terrain and caused an elongated, north–south moisture band to be displaced to the west such that the OMCS develops in the outer region of Fengshen rather than spiraling into the center. Strong northeasterly vertical wind shear contributed to frictional convergence in the boundary layer, and then the large moisture flux convergence in this moisture band led to the downstream development of the OMCS when the band interacted with the monsoon flow. As the OMCS developed in the region of low-level monsoon westerlies and midlevel northerlies associated with the outer circulation of Fengshen, the characteristic structure of a rear-fed inflow with a leading stratiform rain area in the cross-line direction (toward the south) was established. A cold pool (Δθ < −3 K) associated with the large stratiform precipitation region led to continuous formation of new cells at the leading edge of the cold pool, which contributed to the long duration of the OMCS.

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 Analysis of a Tornadic Mesoscale Convective Vortex Based on Ensemble Kalman Filter Assimilation of CASA X-Band and WSR-88D Radar Data

2011 ◽  
Vol 139 (11) ◽  
pp. 3446-3468 ◽  
Author(s):  
Nathan Snook ◽  
Ming Xue ◽  
Youngsun Jung
Keyword(s):  
Kalman Filter ◽  
High Resolution ◽  
Ensemble Kalman Filter ◽  
Weather Prediction ◽  
Radar Data ◽  
Convective System ◽  
Foundation Engineering ◽  
X Band ◽  
Regional Prediction ◽  
Mesoscale Convective

Abstract One of the goals of the National Science Foundation Engineering Research Center (ERC) for Collaborative Adaptive Sensing of the Atmosphere (CASA) is to improve storm-scale numerical weather prediction (NWP) by collecting data with a dense X-band radar network that provides high-resolution low-level coverage, and by assimilating such data into NWP models. During the first spring storm season after the deployment of four radars in the CASA Integrated Project-1 (IP-1) network in southwest Oklahoma, a tornadic mesoscale convective system (MCS) was captured by CASA and surrounding Weather Surveillance Radars-1988 Doppler (WSR-88Ds) on 8–9 May 2007. The MCS moved across northwest Texas and western and central Oklahoma; two tornadoes rated as category 1 on the enhanced Fujita scale (EF-1) and one tornado of EF-0 intensity were reported during the event, just to the north of the IP-1 network. This was the first tornadic convective system observed by CASA. To quantify the impacts of CASA radar data in storm-scale NWP, a set of data assimilation experiments were performed using the Advanced Regional Prediction System (ARPS) ensemble Kalman filter (EnKF) system configured with full model physics and high-resolution terrain. Data from four CASA IP-1 radars and five WSR-88Ds were assimilated in some of the experiments. The ensemble contained 40 members, and radar data were assimilated every 5 min for 1 h. While the assimilation of WSR-88D data alone was able to produce a reasonably accurate analysis of the convective system, assimilating CASA data in addition to WSR-88D data is found to improve the representation of storm-scale circulations, particularly in the lowest few kilometers of the atmosphere, as evidenced by analyses of gust front position and comparison of simulated Vr with observations. Assimilating CASA data decreased RMS innovation of the resulting ensemble mean analyses of Z, particularly in early assimilation cycles, suggesting that the addition of CASA data allowed the EnKF system to more quickly achieve a good result. Use of multiple microphysics schemes in the forecast ensemble was found to alleviate underdispersion by increasing the ensemble spread. This work is the first assimilating real CASA data into an NWP model using EnKF.

Tropical Oceanic Mesoscale Cold Pools in High-Resolution Global Icosahedral Nonhydrostatic (ICON) Model from DYAMOND

2021 ◽  
Author(s):  
Piyush Garg ◽  
Stephen W. Nesbitt ◽  
Timothy J. Lang ◽  
George Priftis
Keyword(s):  
High Resolution ◽  
Linear Regression ◽  
Diurnal Cycle ◽  
General Circulation ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Pool Size ◽  
Cold Pool ◽  
Convective System ◽  
Cold Pools

<p>In the recent years, global kilometer-scale convection-permitting models have shown promising results in producing realistic convection and precipitation. In this study, a 2.5 km global Icosahedral Nonhydrostatic (ICON) model simulation ran for 40 days (06 UTC 01 Aug – 23 UTC 10 Aug 2016) from Dynamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) initiative was used to identify thermal cold pools (using virtual temperature) over tropical oceans. In addition to examining cold pool variability, variables such as vertical wind shear (0-600 hPa and 0-300 hPa), relative humidity, convective available potential energy (CAPE), column water vapor and surface fluxes corresponding to each cold pool were analyzed. Grid-point linear regression was applied to identify relationships between these variables and cold pool size and intensity. It was found out that there is a statistically significant regional variability in the relationships between cold pool properties and their environments across the global tropics, and cold pool size and intensity have quite different dependence on the various variables considered. Unsupervised machine learning algorithm was then applied to geospatial linear regression to identify coherent patterns explaining multi-modal feedback between cold pools and their mesoscale environments.</p><p>Previous studies have hypothesized that although accurate characterization of cold pool diurnal cycle is essential to resolve realistic deep convection in the current generation climate models, our lack of understanding of feedbacks between cold pools and convection leads to distorted diurnal cycle of precipitation. NASA’s RapidScat satellite was in a non-sun-synchronous orbit for 2014-2016 and thus was able to resolve diurnal cycle. Garg et al. (2020) gradient feature technique was applied on RapidScat’s winds to identify cold pools and observe their diurnal cycle of number, size, precipitation and associated convective system properties. Once an observed perspective of cold pool diurnal cycle is obtained, Fourier analysis was used on all the cold pool-associated variables in ICON simulation to obtain the diurnal phase and amplitude. The simulated diurnal cycle of cold pool number, size, precipitation, and other variables were observed to be similar as RapidScat. In this way, this study creates a holistic overview of cold pool-convection-precipitation-storm environment relationships using high-resolution CRM from DYAMOND and satellite observations.</p>

scholarly journals Synoptic and Mesoscale Analysis of a High-Latitude Derecho–Severe Thunderstorm Outbreak in Finland on 5 July 2002

2006 ◽  
Vol 21 (5) ◽  
pp. 752-763 ◽  
Author(s):  
Ari-Juhani Punkka ◽  
Jenni Teittinen ◽  
Robert H. Johns
Keyword(s):  
Potential Temperature ◽  
Leading Edge ◽  
The United States ◽  
Wind Damage ◽  
Cold Pool ◽  
Convective System ◽  
Synoptic Situation ◽  
Large Area ◽  
Synoptic Pattern ◽  
Bow Echo

Abstract On 5 July 2002, a rapidly propagating bow echo formed over eastern Finland causing severe wind damage in an exceptionally large area. The Ministry of the Interior’s Emergency Response Centers received nearly 400 thunderstorm-related wind damage reports. The 5 July 2002 case is the highest-latitude derecho that has ever been documented. The bow echo developed ahead of a northeastward-moving 500-hPa trough inside of the warm sector of a secondary low and moved north-northwestward on the eastern (warm) side of the quasi-stationary front. The leading edge of the bow echo was oriented perpendicular to the low-level southerly wind shear and the convective system propagated along the 850-hPa equivalent potential temperature ridge with a speed that was close to the maximum wind throughout the troposphere. It is particularly noteworthy that the synoptic pattern was oriented about 90° counterclockwise when compared with the typical synoptic pattern associated with warm season derechos in the United States. This kind of synoptic situation associated along with the derecho mesoscale convective system’s (MCS’s) motion toward the north-northwest has not been mentioned in literature before. The MCS started as a cluster of thunderstorms and became a bow echo a few hours later. The leading edge of the bow echo had a strong reflectivity gradient and the region of stratiform precipitation was behind the strongest echoes. At the most intense stage, a rear-inflow notch was visible both in radar and satellite pictures. It was in good accordance with the location of an area of the most severe damage. Moreover, the storm-relative winds derived from the proximity sounding in the wake of the system showed the existence of rear-to-front flow above 850 hPa. The downdraft air appeared to originate from 4 km ASL, where the relative humidity was less than 50%. This probably led to enhanced evaporative cooling and the intense cold pool, which propagated faster than the mean wind. In the mesoscale, the 5 July 2002 derecho had many similarities to other derecho MCSs that have been described in the literature.

Observational Study of the Thermodynamics and Morphological Characteristics of a Midlatitude Continental Cold Pool Event

2020 ◽  
Vol 148 (2) ◽  
pp. 719-737 ◽  
Author(s):  
Paloma Borque ◽  
Stephen W. Nesbitt ◽  
Robert J. Trapp ◽  
Sonia Lasher-Trapp ◽  
Mariko Oue
Keyword(s):  
Life Cycle ◽  
Great Plains ◽  
Climate Models ◽  
Temporal Frequency ◽  
Morphological Characteristics ◽  
Leading Edge ◽  
Propagation Speed ◽  
Cold Pool ◽  
Convective System ◽  
Physical Constraints

Abstract Convectively generated cold pools are important to the Earth system as they exert strong controls on deep convective-storm initiation, intensity, and life cycle. Despite their importance, efforts to introduce such cold pool controls into weather and climate models lack guidance and/or physical constraints from cold pool observations. This work presents a detailed, purely observational analysis of a cold pool event that took place on 23–24 May 2011 in north-central Oklahoma. The characteristics of the cold pool, and the spatiotemporal evolution of the hydrometeors and dynamics in the proximity of the cold pool, are studied with high-resolution observations. The unprecedented dataset used in this work to study cold pool characteristics includes an enhanced network of surface weather stations, a high-temporal-frequency sounding array, and the NEXRAD and Atmospheric Radiation Measurement (ARM) Southern Great Plains radar networks. The potential use of NEXRAD surveillance scans to estimate height and propagation speed of the leading edge of the cold pool (LECP) is presented in this work. Manual identification and tracking of the LECP from NEXRAD imagery shows a spatial and temporal heterogeneity of the LECP properties. Surprisingly, over its detected life cycle, the LECP speed remains almost constant, even though the strength of the cold pool diminishes in time and its height varies. Radar analysis shows that pulses of graupel and hail within downdrafts in the convective system generating the cold pool appeared to be related to temporary increases in the LECP height.

The Role of Momentum Transport in the Motion of a Quasi-Idealized Mesoscale Convective System

2009 ◽  
Vol 137 (10) ◽  
pp. 3316-3338 ◽  
Author(s):  
Kelly M. Mahoney ◽  
Gary M. Lackmann ◽  
Matthew D. Parker
Keyword(s):  
Wind Field ◽  
Mesoscale Convective System ◽  
Leading Edge ◽  
Propagation Speed ◽  
Momentum Transport ◽  
Cold Pool ◽  
Convective System ◽  
Vertical Advection ◽  
Mesoscale Convective

Abstract Momentum transport is examined in a simulated midlatitude mesoscale convective system (MCS) to investigate its contribution to MCS motion. Momentum budgets are computed using model output to quantify the role of specific processes in determining the low-level wind field in the system’s surface-based cold pool. Results show that toward the leading convective line of the MCS and near the leading edge of the cold pool, the momentum field is most strongly determined by the vertical advection of the storm-induced perturbation wind. Across the middle rear of the system, the wind field is largely a product of the pressure gradient acceleration and, to a lesser extent, the vertical advection of the background environmental (i.e., base state) wind. The relative magnitudes of the vertical advection terms in an Eulerian momentum budget suggest that, for gust-front-driven systems, downward momentum transport by the MCS is a significant driver of MCS motion and potentially severe surface winds. Results further illustrate that the contribution of momentum transport to MCS speed occurs mainly via the enhancement of the cold pool propagation speed as higher-momentum air from aloft is transported into the surface-based cold pool.

scholarly journals Impact of the Cold Pool on Mesoscale Convective System–Produced Extreme Rainfall over Southeastern South Korea: 7 July 2009

2016 ◽  
Vol 144 (10) ◽  
pp. 3985-4006 ◽  
Author(s):  
Jong-Hoon Jeong ◽  
Dong-In Lee ◽  
Chung-Chieh Wang
Keyword(s):  
South Korea ◽  
Mesoscale Convective System ◽  
Leading Edge ◽  
Extreme Rainfall ◽  
Cold Pool ◽  
Convective System ◽  
Precipitation Pattern ◽  
Extreme Rainfall Event ◽  
Simulated Precipitation ◽  
Mesoscale Convective

In this study, an extreme rainfall-producing quasi-stationary mesoscale convective system (MCS) associated with the Changma front in southeastern South Korea is investigated using numerical simulations and sensitivity tests. A record-breaking rainfall amount was recorded in response to repeated initiation of new cells (i.e., back-building) over the same area for several hours. The aim of this study is to realistically simulate and analyze this extreme rainfall event to better understand an impact of the cold pool that leads to the quasi-stationary MCS over southeastern South Korea by using a convection-allowing-resolution (2 km) nonhydrostatic atmospheric model. The control experiment (CNTL) was successfully performed, yielding the quasi-stationary, back-building MCS at approximately the correct location and time. In the CNTL run, diabatic cooling due to evaporation of raindrops was responsible for the formation of the cold pool. The development of the cold pool was responsible for the deceleration of the propagating convective line, which played a role in the stalling of the MCS over southeastern South Korea. Moreover, new convective cells were repeatedly initiated in the region where an oncoming warm inflow met the leading edge of the cold pool and was uplifted. In an experiment without evaporative cooling (NOEVA), the simulated precipitation pattern was shifted to the northeast because the MCS became nonstationary without the cold pool. The cold pool had an essential role in the stationarity of the MCS, which resulted in extreme rainfall over the Busan metropolitan area.

The Use of a Modified Ebert–McBride Technique to Evaluate Mesoscale Model QPF as a Function of Convective System Morphology during IHOP 2002

2006 ◽  
Vol 21 (3) ◽  
pp. 288-306 ◽  
Author(s):  
Jeremy S. Grams ◽  
Willam A. Gallus ◽  
Steven E. Koch ◽  
Linda S. Wharton ◽  
Andrew Loughe ◽  
...  
Keyword(s):  
Mesoscale Model ◽  
Mesoscale Convective System ◽  
Radar Data ◽  
Cold Pool ◽  
Convective System ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Almost All ◽  
Rain Rates ◽  
Average Rain

Abstract The Ebert–McBride technique (EMT) is an entity-oriented method useful for quantitative precipitation verification. The EMT was modified to optimize its ability to identify contiguous rain areas (CRAs) during the 2002 International H2O Project (IHOP). This technique was then used to identify systematic sources of error as a function of observed convective system morphology in three 12-km model simulations run over the IHOP domain: Eta, the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5), and the Weather Research and Forecasting (WRF). The EMT was fine-tuned to optimize the pattern matching of forecasts to observations for the scales of precipitation systems observed during IHOP. To investigate several error measures provided by the EMT, a detailed morphological analysis of observed systems was performed using radar data for all CRAs identified in the IHOP domain. The modified EMT suggests that the Eta Model produced average rain rates, peak rainfall amounts, and total rain volumes that were lower than observed for almost all types of convective systems, likely because of its production of overly smoothed and low-variability quantitative precipitation forecasts. The MM5 and WRF typically produced average rain rates and peak rainfall amounts that were larger than observed in most linear convective systems. However, the rain volume for these models was too low for almost all types of convective systems, implying a sizeable underestimate in areal coverage. All three models forecast rainfall too far northwest for linear systems. The results for the WRF and MM5 are consistent with previous observations of mesoscale models run with explicit microphysics and no convective parameterization scheme, suggesting systematic problems with the prediction of mesoscale convective system cold pool dynamics.

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