Microphysical Characteristics of an Asymmetric Eyewall in Major Hurricane Harvey (2017)

Abstract

Microphysical and kinematic structures of major Hurricane Harvey's (2017) asymmetric eyewall are analyzed from ground‐based polarimetric and airborne Doppler radars. New polarimetric observations of differential reflectivity (ZDR) and specific differential phase (KDP) show asymmetric wavenumber‐1 patterns associated with vertical wind shear (VWS) but were shifted azimuthally with respect to the reflectivity (ZH) asymmetry. A ZDR column was found upwind of the ZH maximum in a region with strong updrafts estimated from multi‐Doppler synthesis, with higher values of KDP found cyclonically downwind. Retrieved raindrop size distributions show that azimuthal variations of size and number concentration were determined by both the VWS and the size sorting process. The diameter of raindrops decreases, while the number concentration increases cyclonically downwind of VWS‐induced updrafts due to the differential terminal fall speed of raindrops and strong rotational flow at major hurricane wind speeds.

Hydrometeor Size Sorting in the Asymmetric Eyewall of Hurricane Matthew (2016)

“…The Z DR and K DP columns were spatially offset, with the Z DR column centered in the downshear direction and the K DP column downwind within the DL quadrant. Because the Z DR column can be used as a proxy for the location of maximum updraft, the azimuthal offset of the K DP and Z DR columns is indicative of size sorting of raindrops within the eyewall (e.g., Didlake & Kumjian, 2018; Feng & Bell, 2018; Kumjian & Ryzhkov, 2012). The larger raindrops have faster terminal velocities and thus fall out of the updraft quicker than the smaller, abundant raindrops that are advected further downwind by the primary circulation.…”

“…Size sorting can be maintained by the presence of updrafts or nonzero storm‐relative winds typically associated with wind shear (Dawson et al, 2015; Kumjian & Ryzhkov, 2012) and has been documented in supercells (Crowe et al, 2010; Dawson et al, 2014; Kumjian & Ryzhkov, 2008, 2009; Martinaitis, 2017), continental quasi‐linear convective storms (Loeffler & Kumjian, 2018), and shallow precipitation (Kumjian & Ryzhkov, 2012). Feng and Bell (2018) analyzed polarimetric radar observations of Hurricane Harvey (2017) as it exhibited a wavenumber‐1 asymmetry due to moderate wind shear (7 m s −1 ). They found that the left‐of‐shear eyewall Z H maximum was collocated with a radar size‐sorting signature associated with an azimuthal variation in the eyewall's DSD.…”

Evaluation of Simulated Drop Size Distributions and Microphysical Processes Using Polarimetric Radar Observations for Landfalling Typhoon Matmo (2014)

“…Microphysical parameterizations (MPs) have been widely used in numerical weather prediction models to represent complex cloud microphysical and precipitation processes. Nonlinear interactions between microphysical and dynamical processes through latent heat release and absorption in microphysical processes are particularly critical for TC forecasts (Didlake & Kumjian, ; Feng & Bell, ; Igel et al, ). To describe the complex microphysical processes, more complicated MP schemes have been developed that include more hydrometeor species, more physical processes, and higher degrees of freedom in describing the particle size distribution (PSD) functions.…”

Regional Variability of Precipitation in Tropical Cyclones Over the Western North Pacific Revealed by the GPM Dual‐Frequency Precipitation Radar and Microwave Imager

“…The microphysics of the eyewall (EW) and rainbands in TCs that make landfall have been revealed using disdrometers and polarimetric radars in many studies (Chang et al, ; Didlake & Kumjian, ; Feng & Bell, ; May et al, ; Tokay et al, ; Wang et al, ; Wang et al, ; Wu et al, ). However, TCs spend most of their lifetime over the open ocean, where conventional ground‐based radar observations are scarce (Cecil et al, ; Hence & Houze, , ; Jiang et al, ; Yang et al, ).…”