Polarimetric Radar Observations at Low Levels during Tornado Life Cycles in a Small Sample of Classic Southern Plains Supercells*

Abstract

Preliminary schematics of polarimetric signatures at low levels in southern plains classic supercells are developed for pretornado, tornado, and tornado demise times from a small collection of cases, most of which are cyclic tornado producers. Characteristic signatures and patterns are identified for the reflectivity factor (Z HH ), the differential reflectivity (Z DR ), the correlation coefficient ( hv ), and the specific differential phase (K DP ). Signatures likely related to an ongoing tornado are also discussed. Major findings in Z HH at tornado times include "wings" of higher values often extending away from the updraft region, a stronger gradient on the west side of the echo appendage, and a local maximum at the storm location favorable for tornadogenesis. Increasing cyclonic curvature of the hook-echo region was noted through the tornado life cycle. The Z DR tended to indicate hail shafts most commonly at tornado times, with the highest storm values typically located along the storm's forward flank throughout the tornado life cycle. A Z DR minimum often occurred at the tornado-favorable location, while low Z DR occasionally trailed the tornado region. Stormminimum hv typically occurred at the tornado-favorable location at tornado times and in hail shafts or heavy rain areas at other times. Another region of low correlation was the storm updraft, while the highest storm correlation was typically found in the downwind light-precipitation shield. The K DP typically exhibited a storm-core temporal maximum at tornado times, with the highest storm values in regions of hail and heavy rain and the lowest values in the downwind light-precipitation region. Values in the tornadofavorable region were typically near zero and sometimes strongly negative.

Polarimetric Signatures in Supercell Thunderstorms

“…Van Den Broeke et al (2008) report qualitatively that hail shafts as inferred from high Z HH and low Z DR are present most often at times leading up to tornadogenesis in the few cases they investigated. It is clear from the present analysis that the relationship between the hail signature appearance and tornado presence is weak and highly dependent on the individual storm characteristics, which can differ substantially in different climate regions; for example, Oklahoma (Great Plains) supercells produce very large hail more often than Alabama (Gulf Coast) storms (Doswell et al 2005).…”

“…Recent work by Van Den Broeke et al (2008) analyzes multiple supercell cases. They present a preliminary climatology of polarimetric characteristics of southern Great Plains classic supercells, describing the temporal evolution of the polarimetric variables for several tornadic storms.…”

Characteristics of flash initiations in a supercell cluster with tornadoes

“…The details on the dual-polarization variables were provided by Kumjian (2013a, b, and c). Studies on the polarimetric characteristics of supercells can be found in Dotzek et al (2001), Loney et al (2002), Kumjian and Ryzhkov (2008), Van Den Broeke et al (2008), Snyder et al (2010Snyder et al ( , 2013, Palmer et al (2011), among others.…”

Drop-Size Distributions in Thunderstorms Measured by Optical Disdrometers during VORTEX2

“…With the growing number of polarimetric Doppler weather radars, many studies have provided detailed observations of wind, hydrometeor type and distribution, and radar reflectivity within supercell thunderstorms (e.g., Bringi et al 1991Bringi et al , 1996Smyth and Illingworth 1998;Kennedy and Rutledge 1995;Hubbert et al 1998;Wurman and Gill 2000;Burgess et al 2002;Ryzhkov et al 2005;Bluestein et al 2007;Kumjian andRyzhkov 2008, 2009;Romine et al 2008;Van Den Broeke et al 2008). While polarimetric radar observations can provide information related to the microphysical character of thunderstorms, the microphysics of the near-surface environment, believed to be most important for tornadogenesis, is usually below the radar horizon of even mobile polarimetric radar platforms.…”