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 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.

Surface Characteristics of Observed Cold Pools

2008 ◽  
Vol 136 (12) ◽  
pp. 4839-4849 ◽  
Author(s):  
Nicholas A. Engerer ◽  
David J. Stensrud ◽  
Michael C. Coniglio
Keyword(s):  
Life Cycle ◽  
Potential Temperature ◽  
Surface Characteristics ◽  
Life Cycle Stage ◽  
Cold Pool ◽  
Convective System ◽  
Cold Pools ◽  
Equivalent Potential ◽  
Life Cycle Stages ◽  
The Mean

Abstract Cold pools are a key element in the organization of precipitating convective systems, yet knowledge of their typical surface characteristics is largely anecdotal. To help to alleviate this situation, cold pools from 39 mesoscale convective system (MCS) events are sampled using Oklahoma Mesonet surface observations. In total, 1389 time series of surface observations are used to determine typical rises in surface pressure and decreases in temperature, potential temperature, and equivalent potential temperature associated with the cold pool, and the maximum wind speeds in the cold pool. The data are separated into one of four convective system life cycle stages: first storms, MCS initiation, mature MCS, and MCS dissipation. Results indicate that the mean surface pressure rises associated with cold pools increase from 3.2 hPa for the first storms’ life cycle stage to 4.5 hPa for the mature MCS stage before dropping to 3.3 hPa for the dissipation stage. In contrast, the mean temperature (potential temperature) deficits associated with cold pools decrease from 9.5 (9.8) to 5.4 K (5.6 K) from the first storms to the dissipation stage, with a decrease of approximately 1 K associated with each advance in the life cycle stage. However, the daytime and early evening observations show mean temperature deficits over 11 K. A comparison of these observed cold pool characteristics with results from idealized numerical simulations of MCSs suggests that observed cold pools likely are stronger than those found in model simulations, particularly when ice processes are neglected in the microphysics parameterization. The mean deficits in equivalent potential temperature also decrease with the MCS life cycle stage, starting at 21.6 K for first storms and dropping to 13.9 K for dissipation. Mean wind gusts are above 15 m s−1 for all life cycle stages. These results should help numerical modelers to determine whether the cold pools in high-resolution models are in reasonable agreement with the observed characteristics found herein. Thunderstorm simulations and forecasts with thin model layers near the surface are also needed to obtain better representations of cold pool surface characteristics that can be compared with observations.

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 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.

scholarly journals A Study of the Role of Daytime Land–Atmosphere Interactions on Nocturnal Convective Activity in the Southern Great Plains during CLASIC

2014 ◽  
Vol 15 (5) ◽  
pp. 1932-1953 ◽  
Author(s):  
Jessica M. Erlingis ◽  
Ana P. Barros
Keyword(s):  
Boundary Layer ◽  
Great Plains ◽  
Land Surface ◽  
Initial Conditions ◽  
Cold Pool ◽  
Convective System ◽  
Temporal Scales ◽  
Spatial And Temporal Scales ◽  
Southern Great Plains ◽  
Low Level

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.

Observations of Elevated Convection Initiation Leading to a Surface-Based Squall Line during 13 June IHOP_2002

2011 ◽  
Vol 139 (1) ◽  
pp. 247-271 ◽  
Author(s):  
John H. Marsham ◽  
Stanley B. Trier ◽  
Tammy M. Weckwerth ◽  
James W. Wilson
Keyword(s):  
Local Time ◽  
Great Plains ◽  
Doppler Radar ◽  
Mesoscale Convective System ◽  
The United States ◽  
Squall Line ◽  
Cold Pool ◽  
Convective System ◽  
Near Surface ◽  
Wave Trapping

Abstract The evolution of a mesoscale convective system (MCS) observed during the International H2O Project that took place on the Great Plains of the United States is described. The MCS formed at night in a frontal zone, with four initiation episodes occurring between approximately 0000 and 0400 local time. Radar, radiosonde, and surface data together show that at least three of the initiation episodes were elevated, occurring from moist conditionally unstable layers located above the boundary layer, which had been stabilized by previous MCSs. Initiation occurred in northwest–southeast-oriented lines where a southerly nocturnal low-level jet terminated, generating elevated convergence. One initiation episode was observed using the S-band dual-polarization Doppler radar (S-Pol) and occurred at the intersection of this convergence zone with a propagating wave. Calculations of the Scorer parameter were consistent with wave trapping. Downdrafts from the developing convection generated both waves and bores, which propagated ahead of the cold pool, initiating further convection. Between 0700 and 1000 local time, the structure and orientation of the MCS evolved to a southwest–northeast-oriented squall line, which built a cold-pool outflow that could lift near-surface air to its level of free convection. The weaker cold pool in the eastern part of the domain was consistent with the greater impacts of a previous MCS there. To the authors’ knowledge, this case study provides the first detailed observational investigation of elevated initiation leading to surface-based convection, a process that appears to be an important mechanism for the generation of long-lived MCSs from elevated initiation.

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.

scholarly journals On the Relationship of Cold Pool and Bulk Shear Magnitudes on Upscale Convective Growth in the Great Plains of the United States

Atmosphere ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 1019
Author(s):  
Zachary A. Hiris ◽  
William A. Gallus
Keyword(s):  
United States ◽  
Great Plains ◽  
Prediction Models ◽  
Weather Prediction ◽  
Vertical Wind Shear ◽  
The United States ◽  
Growth Potential ◽  
Cold Pool ◽  
Convective System ◽  
The Impact

Upscale convective growth remains a poorly understood aspect of convective evolution, and numerical weather prediction models struggle to accurately depict convective morphology. To better understand some physical mechanisms encouraging upscale growth, 30 warm-season convective events from 2016 over the United States Great Plains were simulated using the Weather Research and Forecasting (WRF) model to identify differences in upscale growth and non-upscale growth environments. Also, Bryan Cloud Model (CM1) sensitivity tests were completed using different thermodynamic environments and wind profiles to examine the impact on upscale growth. The WRF simulations indicated that cold pools are significantly stronger in cases that produce upscale convective growth within the first few hours following convective initiation compared to those without upscale growth. Conversely, vertical wind shear magnitude has no statistically significant relationship with either MCS or non-MCS events. This is further supported by the CM1 simulations, in which tests using the WRF MCS sounding developed a large convective system in all tests performed, including one which used the non-MCS kinematic profile. Likewise, the CM1 simulations of the non-upscale growth event did not produce an MCS, even when using the MCS kinematic profile. Overall, these results suggest that the near-storm and pre-convective thermodynamic environment may play a larger role than kinematics in determining upscale growth potential in the Great Plains.

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.

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