Enhanced Polarimetric Radar Signatures above the Melting Level in a Supercell Storm

Abstract

Compelling in situ and polarimetric radar observations from a severe Oklahoma supercell storm are presented. The in situ observations are from an aircraft that entered the storm above the main inflow region, sampling the embryo curtain, main updraft, its western fringe (very close to the center of mesocyclonic circulation), and the hail cascade region. At the same time, the Cimarron polarimetric radar observed enhanced signatures in specific differential phase Kdp and differential reflectivity Zdr straddling the main updraft and extending several kilometers above the melting layer. The distance of the storm from the radar balances the novelty of this dataset, however, which is on the order of 100 km. The authors therefore rely heavily on the in situ data, including calculation of polarimetric variables, on comparisons with other in situ datasets, and on accepted conceptual models of hail growth in supercell storms to clarify hydrometeor processes in light of the intriguing polarimetric signatures near the updraft. The relation of enhanced Kdp to the main updraft, to the Zdr ?column,? and to precipitation is discussed. Strong evidence points to melting ice particles (>3 mm) below the aircraft height as the origin of the Kdp column in the region where an abundant number of small (<2 mm) drops are also observed. To support the notion that these drops are shed by melting and perhaps wet growth, results of calculations on aircraft data are discussed. Resolution issues are invoked, leading to possible reconciliation of radar measurements with in situ observations.