VDRAS and Polarimetric Radar Investigation of a Bow Echo Formation After a Squall Line Merged With a Preline Convective Cell

Abstract This study explores both the practical and intrinsic predictability of severe convective weather at the mesoscales using convection-permitting ensemble simulations of a squall line and bow echo event during the Bow Echo and Mesoscale Convective Vortex (MCV) Experiment (BAMEX) on 9–10 June 2003. Although most ensemble members—initialized with realistic initial condition uncertainties smaller than the NCEP Global Forecast System Final Analysis (GFS FNL) using an ensemble Kalman filter—forecast broad areas of severe convection, there is a large variability of forecast performance among different members, highlighting the limit of practical predictability. In general, the best-performing members tend to have a stronger upper-level trough and associated surface low, producing a more conducive environment for strong long-lived squall lines and bow echoes, once triggered. The divergence in development is a combination of a dislocation of the upper-level trough, surface low with corresponding marginal environmental differences between developing and nondeveloping members, and cold pool evolution by deep convection prior to squall line formation. To further explore the intrinsic predictability of the storm, a sequence of sensitivity experiments was performed with the initial condition differences decreased to nearly an order of magnitude smaller than typical analysis and observation errors. The ensemble forecast and additional sensitivity experiments demonstrate that this storm has a limited practical predictability, which may be further improved with more accurate initial conditions. However, it is possible that the true storm could be near the point of bifurcation, where predictability is intrinsically limited. The limits of both practical and intrinsic predictability highlight the need for probabilistic and ensemble forecasts for severe weather prediction.

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Analysis of Dual-Polarimetric Radar Variables and Quantitative Precipitation Estimators for Landfall Typhoons and Squall Lines Based on Disdrometer Data in Southern China

Atmosphere ◽

10.3390/atmos10010030 ◽

2019 ◽

Vol 10 (1) ◽

pp. 30 ◽

Cited By ~ 3

Author(s):

Yonghua Zhang ◽

Liping Liu ◽

Shuoben Bi ◽

Zhifang Wu ◽

Ping Shen ◽

...

Keyword(s):

Drop Size ◽

Southern China ◽

Average Diameter ◽

Squall Line ◽

Polarimetric Radar ◽

Quantitative Precipitation Estimation ◽

Squall Lines ◽

Fitting Method ◽

Precipitation Estimation ◽

Differential Reflectivity

Typhoon rainstorms often cause disasters in southern China. Quantitative precipitation estimation (QPE) with the use of polarimetric radar can improve the accuracy of precipitation estimation and enhance typhoon defense ability. On the basis of the observed drop size distribution (DSD) of raindrops, a comparison is conducted among the DSD parameters and the polarimetric radar observation retrieved from DSD in five typhoon and three squall line events that occurred in southern China from 2016 to 2017. A new piecewise fitting method (PFM) is used to develop the QPE estimators for landfall typhoons and squall lines. The performance of QPE is evaluated by two fitting methods for two precipitation types using DSD data collected. Findings indicate that the number concentration of raindrops in typhoon precipitation is large and the average diameter is small, while the raindrops in squall line rain have opposite characteristics. The differential reflectivity (ZDR) and specific differential phase (KDP) in these two precipitation types increase slowly with the reflectivity factor (ZH), whereas the two precipitation types have different ZDR and KDP in the same ZH. Thus, it is critical to fit the rainfall estimator for different precipitation types. Enhanced estimation can be obtained using the estimators for specific precipitation types, whether the estimators are derived from the conventional fitting method (CFM) or PFM, and the estimators fitted using the PFM can produce better results. The estimators for the developed polarimetric radar can be used in operational QPE and quantitative precipitation foresting, and they can improve disaster defense against typhoons and heavy rains.

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Development and Forcing of the Rear Inflow Jet in a Rapidly Developing and Decaying Squall Line during BAMEX

Monthly Weather Review ◽

10.1175/2008mwr2503.1 ◽

2009 ◽

Vol 137 (4) ◽

pp. 1206-1229 ◽

Cited By ~ 23

Author(s):

Joseph A. Grim ◽

Robert M. Rauber ◽

Greg M. McFarquhar ◽

Brian F. Jewett ◽

David P. Jorgensen

Keyword(s):

Pressure Gradient ◽

Dynamic Pressure ◽

Radar Data ◽

Squall Line ◽

System Evolution ◽

Formative Stage ◽

Bow Echo ◽

Mesoscale Convective ◽

Forcing Mechanisms ◽

Inflow Jet

Abstract This study examines the development, structure, and forcing of the rear inflow jet (RIJ) through the life cycle of a small, short-lived squall line over north-central Kansas on 29 June 2003. The analyses were developed from airborne quad-Doppler tail radar data from the NOAA and NRL P-3 aircraft, obtained over a 2-h period encompassing the formation, development, and decay of the squall line during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). The strengthening of the system-relative rear inflow to 17 m s−1 was concurrent with the formation of a bow echo, an increased dynamic pressure gradient beneath the rearward-tilted updraft, and two counterrotating vortices at either end of the bow. The later weakening of the RIJ to 8 m s−1 was concurrent with the weakening of the bow, a decreased dynamic pressure gradient at midlevels behind the bow, and the weakening and spreading of the vortices. In a modeling study, Weisman quantified the forcing mechanisms responsible for the development of an RIJ. This present study is the first to quantitatively analyze these mechanisms using observational data. The forcing for the horizontal rear inflow was analyzed at different stages of system evolution by evaluating the contributions of four forcing mechanisms: 1) the horizontal pressure gradient resulting from the vertical buoyancy distribution (δPB), 2) the dynamic pressure gradient induced by the circulation between the vortices (δPV), 3) the dynamic irrotational pressure gradient (δPI), and 4) the background synoptic-scale dynamic pressure gradient (δPS). During the formative stage of the bow, δPI was the strongest forcing mechanism, contributing 50% to the rear inflow. However, during the mature and weakening stages, δPI switched signs and opposed the rear inflow while the combination of δPB and δPV accounted for at least 70% of the rear inflow. The δPS forced 4%–25% of the rear inflow throughout the system evolution.

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Numerical Simulations of Bow Echo Formation Following a Squall Line–Supercell Merger

Monthly Weather Review ◽

10.1175/mwr-d-13-00356.1 ◽

2014 ◽

Vol 142 (12) ◽

pp. 4791-4822 ◽

Cited By ~ 8

Author(s):

Adam J. French ◽

Matthew D. Parker

Keyword(s):

Numerical Simulations ◽

Vertical Wind Shear ◽

Leading Edge ◽

Direct Result ◽

Squall Line ◽

Cold Pool ◽

Surface Winds ◽

Sensitivity Tests ◽

Bow Echo ◽

Inflow Jet

Abstract Output from idealized numerical simulations is used to investigate the storm-scale processes responsible for squall-line evolution following a merger with an isolated supercell. A simulation including a squall line–supercell merger is compared to one using the same initial squall line and background environment without the merger. These simulations reveal that while bow echo formation is favored by the strongly sheared background environment, the merger produces a more compact bowing structure owing to a locally enhanced rear-inflow jet. The merger also represents a favored location for severe weather production relative to other portions of the squall line, with surface winds, vertical vorticity, and rainfall all being maximized in the vicinity of the merger. An analysis of storm-scale processes reveals that the premerger squall line weakens as it encounters outflow from the preline supercell, and the supercell becomes the leading edge of the merged system. Subsequent localized strengthening of the cold pool and rear-inflow jet produce a compact, intense bow echo local to the merger, with a descending rear-inflow jet creating a broad swath of damaging surface winds. These features, common to severe bow echoes, are shown to be a direct result of the merger in the present simulations, and are diminished or absent in the no-merger simulation. Sensitivity tests reveal that mergers in a weaker vertical wind shear environment do not produce an enhanced bow echo structure, and only produce a localized region of marginally enhanced surface winds. Additional tests demonstrate that the details of postmerger evolution vary with merger location along the line.

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Polarimetric Radar Observations from a Waterspout-Producing Thunderstorm

Weather and Forecasting ◽

10.1175/waf-d-14-00114.1 ◽

2015 ◽

Vol 30 (2) ◽

pp. 329-348 ◽

Cited By ~ 5

Author(s):

Matthew S. Van Den Broeke ◽

Cynthia A. Van Den Broeke

Keyword(s):

Lake Michigan ◽

Convective Cell ◽

Great Lakes Region ◽

Polarimetric Radar ◽

Air Mass ◽

Radar Observations ◽

Potential Source ◽

Western Lake ◽

Low Levels ◽

Differential Reflectivity

Abstract A family of four waterspouts was produced by a convective cell over western Lake Michigan on 12 September 2013. This storm initiated along a boundary north of a mesolow in a low-level cold-air advection regime, and developed supercell characteristics once the second waterspout was in progress. Polarimetric characteristics of the storm, and of the development of supercell character, are presented. These observations represent the first documented polarimetric radar observations of waterspout-producing convection in the Great Lakes region. Unusually high differential reflectivity values accompanied this storm and its initiating boundary. The high values along the boundary are partially explained by a high density of dragonflies. High differential reflectivity values were present through much of the storm of interest despite very low aerosol concentration at low levels in the lake-influenced air mass. Finally, this case illustrates the importance of environmental awareness on waterspout-favorable days, especially when boundaries are nearby to serve as a potential source of enhanced environmental vertical vorticity.

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Observational Analysis of a Wind Gust Event during the Merging of a Bow Echo and Mini-Supercell in Southeastern China

Atmosphere ◽

10.3390/atmos12111511 ◽

2021 ◽

Vol 12 (11) ◽

pp. 1511

Author(s):

Hui Zheng ◽

Yuchun Zhao ◽

Yipeng Huang ◽

Wei Zhang ◽

Changrong Luo ◽

...

Keyword(s):

Convective Cell ◽

Cyclonic Circulation ◽

Wind Gust ◽

Southeastern China ◽

Wind Speeds ◽

Significant Damage ◽

Bow Echo ◽

Layer 4 ◽

Surface Station ◽

Differential Reflectivity

The merging of a fast-moving bow echo with a convective cell of a hook-echo signature was studied by using polarimetric radar detections. Gusts with wind speeds near 35 m s–1 were recorded by the surface station, which caused significant damage. A convective cell with a mesovortex signature, which is hereafter referred to as a mini-supercell, was observed over the northeast of the bow echo before the convective merging. It was found that the mesovortex possessed cyclonic circulation and resembled a supercell-like feature. The merging of the bow echo and the mini-supercell strengthened the updraft near the apex of the bow echo. The enhanced updraft was also demonstrated by the appearance of a differential reflectivity (ZDR) column with a topmost height of 4 km above the melting layer (~4 km). The bow was separated into northern and southern sectors after merging with the mini-supercell, leading to the gusty wind over the surface of the south sector.

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Disdrometer, Polarimetric Radar, and Condensation Nuclei Observations of Supercell and Multicell Storms on 11 June 2018 in Eastern Nebraska

Atmosphere ◽

10.3390/atmos11070770 ◽

2020 ◽

Vol 11 (7) ◽

pp. 770

Author(s):

Matthew Van Den Broeke

Keyword(s):

Particle Concentration ◽

Rain Rate ◽

Radar Data ◽

Convective Cell ◽

Observation Time ◽

Precipitation Intensity ◽

Polarimetric Radar ◽

Condensation Nuclei ◽

Supercell Storm ◽

Differential Reflectivity

Disdrometer and condensation nuclei (CN) data are compared with operational polarimetric radar data for one multicell and one supercell storm in eastern Nebraska on 11 June 2018. The radar was located ~14.3 km from the instrumentation location and provided excellent observation time series with new low-level samples every 1–2 min. Reflectivity derived by the disdrometer and radar compared well, especially in regions with high number concentration of drops and reflectivity <45 dBZ. Differential reflectivity also compared well between the datasets, though it was most similar in the supercell storm. Rain rate calculated by the disdrometer closely matched values estimated by the radar when reflectivity and differential reflectivity were used to produce the estimate. Concentration of CN generally followed precipitation intensity for the leading convective cell, with evidence for higher particle concentration on the edges of the convective cell associated with outflow. The distribution of CN in the supercell was more complex and generally did not follow precipitation intensity.

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Interaction of an Upper-Tropospheric Jet with a Squall Line Originating along a Cold Frontal Boundary

Monthly Weather Review ◽

10.1175/mwr-d-16-0044.1 ◽

2016 ◽

Vol 144 (11) ◽

pp. 4197-4219

Author(s):

Daniel M. Stechman ◽

Robert M. Rauber ◽

Greg M. McFarquhar ◽

Brian F. Jewett ◽

David P. Jorgensen

Keyword(s):

Three Dimensional ◽

Squall Line ◽

Naval Research ◽

Jet Stream ◽

Bow Echo ◽

Mesoscale Convective ◽

Parent Domain ◽

Mesoscale Convective Vortex ◽

Doppler Analysis ◽

Frontal Boundary

Abstract On 8 June 2003, an expansive squall line along a surface cold frontal boundary was sampled during the Bow Echo and Mesoscale Convective Vortex Experiment. The Naval Research Laboratory P-3 aircraft and the National Oceanic and Atmospheric Administration P-3 aircraft simultaneously sampled the leading and trailing edge of this squall line, respectively, with X-band Doppler radars. Data from these two airborne radar systems have been synthesized to produce a pseudo-quad-Doppler analysis of the squall line, yielding a detailed three-dimensional kinematic analysis of its structure. A simulation of the squall line was carried out using the Weather Research and Forecasting Model to complement the pseudo-quad-Doppler analysis. The simulation employed a 3-km, convection-allowing, nested domain centered over the pseudo-quad-Doppler domain, along with a 9-km parent domain to capture the larger synoptic-scale cyclone. The pseudo-quad-Doppler analysis reveals that the convective line was embedded within the upper-tropospheric jet stream, causing local decelerations and deviations in the jet-level flow. The vertical transport of low momentum air from the boundary layer via convective updrafts is shown to significantly decelerate jet-level flow. Pressure perturbations associated with the intrusion of low momentum air into the jet stream–level flow led to deviation of the jet stream flow around the squall line that resulted in counter-rotating ribbons of vertical vorticity parallel to the squall line. Model results indicate that disturbances in the jet stream structure persisted downwind of the squall line for several hours.

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