Dual-polarization radar signatures in snowstorms: Role of snowflake aggregation

AbstractThe characteristics of microphysical processes of a severe winter storm that occurred on the Korean Peninsula on 12 December 2013 was studied in this work for the first time via X-band dual-polarization weather radar observations. A new range–height indicator (RHI) scan-based quasi-vertical profile methodology, in which polarimetric radar variables were averaged at each height of the RHI scan, was introduced to investigate the snow microphysics, and the obtained polarimetric radar signatures served as fingerprints of the dendritic growth, aggregation, and riming processes. Enhanced differential reflectivity (Zdr) and specific differential phase shift (Kdp) bands were detected near the −15°C isotherm, which signified the growth of dendrites or platelike crystals. The observed correlation between the increases in the reflectivity factor at horizontal polarization Zh and copolar correlation coefficient ρhv and the decreases in Zdr and Kdp magnitudes at lower heights suggested the occurrence of the aggregation process. The combination of high Zh and low Zdr values with turbulent atmospheric conditions observed at the ground level indicated the occurrence of the riming process. In addition, the negative Kdp and Zdr values combined with high Zh and ρhv magnitudes (observed near the end of the snow event) indicated the formation of graupel particles. The polarimetric radar signatures obtained for the snow growth processes were evident from ground observations and agreed well with the results of the Weather Research and Forecasting Model and Modern-Era Retrospective Analysis for Research and Applications data. Furthermore, the spatial variability of Zh methodology was implemented to describe both aggregates and rimed ice particles.

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A Random Forest Method to Forecast Downbursts Based on Dual-Polarization Radar Signatures

Remote Sensing ◽

10.3390/rs11070826 ◽

2019 ◽

Vol 11 (7) ◽

pp. 826 ◽

Cited By ~ 2

Author(s):

Bruno Medina ◽

Lawrence Carey ◽

Corey Amiot ◽

Retha Mecikalski ◽

William Roeder ◽

...

Keyword(s):

Random Forest ◽

Prediction Method ◽

The United States ◽

Random Forest Model ◽

Dual Polarization ◽

Forest Model ◽

Random Forest Method ◽

Reliable Performance ◽

Radar Signatures ◽

Kennedy Space

The United States Air Force’s 45th Weather Squadron provides wind warnings, including those for downbursts, at the Cape Canaveral Air Force Station and Kennedy Space Center (CCAFS/KSC). This study aims to provide a Random Forest model that classifies thunderstorms’ downburst and null events using a 35-knot wind threshold to separate these two categories. The downburst occurrence was assessed using a dense network of wind observations around CCAFS/KSC. Eight dual-polarization radar signatures that are hypothesized to have physical implications for downbursts at the surface were automatically calculated for 209 storms and ingested into the Random Forest model. The Random Forest model predicted null events more correctly than downburst events, with a True Skill Statistic of 0.40. Strong downburst events were better classified than those with weaker wind magnitudes. The most important radar signatures were found to be the maximum vertically integrated ice and the peak reflectivity. The Random Forest model presented a more reliable performance than an automated prediction method based on thresholds of single radar signatures. Based on these results, the Random Forest method is suggested for continued operational development and testing.

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C-band Dual-Polarization Radar Signatures of Wet Downbursts around Cape Canaveral, Florida

Weather and Forecasting ◽

10.1175/waf-d-18-0081.1 ◽

2019 ◽

Vol 34 (1) ◽

pp. 103-131 ◽

Cited By ~ 1

Author(s):

Corey G. Amiot ◽

Lawrence D. Carey ◽

William P. Roeder ◽

Todd M. McNamara ◽

Richard J. Blakeslee

Keyword(s):

Warm Season ◽

Threshold Level ◽

Peak Height ◽

Mature Stage ◽

Lead Times ◽

Dual Polarization ◽

Near Surface ◽

Skill Scores ◽

Radar Signatures ◽

Wind Events

Abstract Wind warnings are the second-most-frequent advisory issued by the U.S. Air Force’s 45th Weather Squadron (45WS) at Cape Canaveral, Florida. Given the challenges associated with nowcasting convection in Florida during the warm season, improvements in 45WS warnings for convective wind events are desired. This study aims to explore the physical bases of dual-polarization radar signatures within wet downbursts around Cape Canaveral and identify signatures that may assist the 45WS during real-time convective wind nowcasting. Data from the 45WS’s C-band dual-polarization radar were subjectively analyzed within an environmental context, with quantitative wind measurements recorded by weather tower sensors for 32 threshold-level downbursts with near-surface winds ≥ 35 kt (1 kt ≈ 0.51 m s−1) and 32 null downbursts. Five radar signatures were identified in threshold-level downburst-producing storms: peak height of 1-dB differential reflectivity ZDR column, peak height of precipitation ice signature, peak reflectivity, height below 0°C level where ZDR increases to 3 dB within a descending reflectivity core (DRC), and vertical ZDR gradient within DRC. Examining these signatures directly in updraft–downdraft cycles that produced threshold-level winds yielded mean lead times of 20.0–28.2 min for cumulus and mature stage signatures and 12.8–14.9 min for dissipating stage signatures, with higher signature test values generally yielding higher skill scores. A conceptual test of utilizing signatures within earlier cells in multicell storms to indirectly predict the potential for intense downbursts in later cells was performed, which offered increased lead times and skill scores for an Eulerian forecast region downstream from the storm initiation location.

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POTENTIAL ROLE OF DUAL-POLARIZATION RADAR IN THE VALIDATION OF SATELLITE PRECIPITATION MEASUREMENTS

Bulletin of the American Meteorological Society ◽

10.1175/2008bams2177.1 ◽

2008 ◽

Vol 89 (8) ◽

pp. 1127-1146 ◽

Cited By ~ 59

Author(s):

V. Chandrasekar ◽

Arthur Hou ◽

Eric Smith ◽

V. N. Bringi ◽

S. A. Rutledge ◽

...

Keyword(s):

Potential Role ◽

Dual Polarization ◽

Satellite Precipitation

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Polarimetric Radar Signatures of a Rare Tornado Event over South Korea

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-18-0041.1 ◽

2018 ◽

Vol 35 (10) ◽

pp. 1977-1997 ◽

Cited By ~ 1

Author(s):

S. Lim ◽

S. Allabakash ◽

B. Jang ◽

V. Chandrasekar

Keyword(s):

High Resolution ◽

South Korea ◽

Metropolitan Region ◽

Doppler Velocity ◽

Polarimetric Radar ◽

Dual Polarization ◽

Radar Observations ◽

X Band ◽

Close Range ◽

Radar Signatures

AbstractThe Korea Institute of Civil Engineering and Building Technology (KICT) made one of the first radar observations of a rare tornadic storm that occurred on 10 June 2014 in the Seoul metropolitan region, South Korea, using X-band dual-polarization radar. The tornado lasted for about 18 min, during which it destroyed about 20 greenhouses and injured several people. This tornado was rated at F0 on the Fujita scale. The KICT X-band dual-polarization radar was installed in the area northwest of Seoul to monitor storm development, measure rainfall, improve hazard mitigation, and disaster management. This paper presents the high-resolution (both spatial and temporal) polarimetric radar observations of the tornado, along with the radar parameters of reflectivity, differential reflectivity, Doppler velocity, and copolar correlation coefficient. The characteristic signatures of polarimetric variables, including the descending reflectivity core, weak echo hole, Doppler velocity couplet, and hook echo, are used to describe the tornado vortex and its development. In addition, the close range (about 5-km distance) observations of the hook echo show the high-resolution radar signatures of a weak echo region surrounded by high-reflectivity annular rings inside the tornado vortex. From development to dissipation, various finescale features are observed, including lofted tornadic debris and potential hail signatures. The high-resolution (close range) observations were also compared against low-resolution (long range) radar observations. The comparison shows that high-spatiotemporal, low-altitude, and close-range observations can be significantly advantageous for tornado detection and early warning.

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