Polarimetric Radar Metrics Related to Tornado Life Cycles and Intensity in Supercell Storms

Abstract

Polarimetric radar signatures have been related to the typical evolution of supercell storms, including through tornado life cycles. Now that polarimetric radar observations are available for a large sample of supercell storms, time series of new radar metrics can be derived. These metrics can be compared with phases of known tornado life cycles in an effort to develop new methods of anticipating tornadoes and to increase understanding of storm-scale structural and microphysical changes through supercell and tornado life cycles. In this paper, radar metrics including measures of differential reflectivity ZDR columns, ZDR arcs, polarimetrically inferred hailfall regions, and mean value of copolar correlation coefficient ρhv in the echo appendage are compared to the tornado life cycle and to storm-maximum tornado intensity in a sample of 35 tornadic supercells. It is shown that these radar metrics may change repeatedly and thus can be used to distinguish tornadic and nontornadic periods in single supercell storms, tornadogenesis from tornado demise times, and modes of storm evolution relative to tornadoes (e.g., if a storm produces one tornado or several). The polarimetric radar metrics are nearly as predictive of tornado intensity as commonly used measures of environmental variability for this sample.

Rapid-Update Radar Observations of ZDR Column Depth and Its Use in the Warning Decision Process

“…To date, research has demonstrated that Z DR columns likely provide useful information about storm intensity and potential threats, but little clear information exists to connect them directly to existing conceptual models and warning decisions, thereby limiting a forecaster's ability to leverage the full benefits of dual-pol technology during severe-weather operations (e.g., Kumjian and Ryzhkov 2008;Kumjian 2013). Knowledge gaps also exist regarding Z DR column evolution in nontornadic supercells, column evolution across multiple elevation angles (i.e., volumetric analysis), impact of radar update time on accurate sampling of column evolution, and typical values of Z DR column depth (e.g., Van Den Broeke et al 2008;Picca et al 2015;Van Den Broeke 2017).…”

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

“…Z DR data from the WSR-88D were calibrated following the procedure of [29], which is also applied by [17,30]. From the radar dataset, the low-level scan nearest the midpoint of the disdrometer dataset was selected (~2206 UTC) and all pixels~1.5 km above the ambient 0 • C level in convective anvil regions with 20 dBZ ≤ Z HH ≤ 35 dBZ were selected.…”

“…Atmosphere 2020, 11, x FOR PEER REVIEW 4 of 18 ZDR data from the WSR-88D were calibrated following the procedure of [29], which is also applied by [17,30]. From the radar dataset, the low-level scan nearest the midpoint of the disdrometer…”

“…It develops in response to size sorting in the storm-relative inflow [8,12,13] and may change markedly through time, perhaps indicating changes in the storm-relative wind profile [14,15]. Z DR arc characteristics have been explored as a possible indicator of a storm's tornadic potential [16,17]. The K DP foot [9] is an area of large K DP values typically found in a storm's reflectivity (Z HH ) core downwind from where hail falls out and may indicate high liquid water content (LWC) in melting hail.…”

Earth's Electromagnetic Forces and Their Participation in the Creation of Tornadoes

“…To summarize all that has been said, I want to express the hope that my vision of the nature of the tornado will eventually "curb" this formidable phenomenon, and not only endlessly study its features, as is now happening [17][18][19].…”