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Abstract Downbursts pose a threat to life, property, and aviation, yet they remain challenging to predict. Prior studies have found radar-based downburst signatures such as divergent and convergent velocity signatures at the surface and midlevels, respectively; descending radar reflectivity (Z) cores (DRCs); present or descending specific differential phase (KDP) cores; and troughs of decreased differential reflectivity (ZDR) collocated with decreased copolar correlation coefficient (ρhv) below the melting layer. This research expands on those studies using the multicell identification and tracking (MCIT) algorithm to automate storm detection and analyze 53 downburst cases spanning most regions of the CONUS. Individual case analysis revealed that DRCs appeared in 83% of cases, descendingKDPcores appeared in 85% of cases, andZDRtroughs and collocatedρhvdrops appeared in 89% of cases. The magnitude of low-level divergence and midlevel convergence reached a threshold of 0.0025 s−1in 68% and 83% of cases, respectively. Composite time series revealed that divergence displayed the most prominent signature near the surface; aloft,KDPat and 1 km below the freezing level, midlevel convergence,ZDRcolumn area and volume, and VIL displayed the most prominent signatures. Differences were observed between geographic regions and thermodynamic environments, with lower velocity-related and higherKDP-related values most common in the eastern United States and environments with wind index (WINDEX) < 60; conversely, higher velocity-related and lowerKDP-related values were most common in the western United States and environments with WINDEX > 60. These findings may help inform future polarimetric downburst detection and algorithm development efforts.
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Storms Producing Large Accumulations of Small Hail
Hail-bearing storms produce substantial socioeconomic impacts each year, yet challenges remain in forecasting the type of hail threat supported by a given environment and in using radar to estimate hail sizes more accurately. One class of hail threat is storms producing large accumulations of small hail (SPLASH). This paper presents an analysis of the environments and polarimetric radar characteristics of such storms. Thirteen SPLASH events were selected to encompass a broad range of geographic regions and times of year. Rapid Refresh model output was used to characterize the mesoscale environments associated with each case. This analysis reveals that a range of environments can support SPLASH cases; however, some commonalities included large precipitable water (exceeding that day’s climatological 90th-percentile values), CAPE < 2500 J kg−1, weak storm-relative wind speeds (<10 m s−1) in the lowest few kilometers of the troposphere, and a weak component of the storm-relative flow orthogonal to the 0–6-km shear vector. Most of the storms were weak supercells that featured distinctive S-band radar signatures, including compact (<200 km2) regions of reflectivity factor > 60 dB Z, significant differential attenuation evident as negative differential reflectivity extending downrange of the hail core, and anomalously large specific differential phase KDP. The KDPvalues often approached or exceeded the operational color scale’s upper limit (10.7° km−1); reprocessing the level-II data revealed KDP>17° km−1, the highest documented in precipitation at S band. Electromagnetic scattering calculations using the T-matrix method confirm that large quantities of small melting hail mixed with heavy rain can plausibly explain the observed radar signatures.
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- Award ID(s):
- 1661679
- PAR ID:
- 10086253
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Applied Meteorology and Climatology
- Volume:
- 58
- Issue:
- 2
- ISSN:
- 1558-8424
- Page Range / eLocation ID:
- p. 341-364
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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