Vertical Structure of Hurricane Eyewalls as Seen by the TRMM Precipitation Radar

Abstract

Statistical analysis of the vertical structure of radar echoes in the eyewalls of tropical cyclones, shown by the Tropical Rainfall Measurement Mission (TRMM) Precipitation Radar (PR), shows that the eyewall contains high reflectivities and high echo tops, with deeper and more intense but highly intermittent echo perturbations superimposed on the basic structure. The overall echo strength, height of echo top, and presence of intense echo perturbations all increase with vortex strength. Intense echo perturbations decrease in frequency with low sea surface temperatures. When the PR data are normalized by the amount of radar echo in each sample and examined quadrant by quadrant relative to the direction of the environmental shear, the nature of convective processes in different parts of the eyewall becomes apparent. The normalized statistics of the echo intensity, brightband structure, and maximum echo-top height show that processes generating convective precipitation are generally favored in the downshear-right region of the eyewall, while the nonnormalized statistics indicate that the vertical wind shear determines the placement of precipitation particles downwind of the generation zone such that the precipitation maximum occurs about one quadrant downwind of the convective generation zone. When the track speed exceeds the magnitude of the shear vector, this pattern modifies such that the asymmetry rotates one quadrant to the right. The statistics, moreover, indicate that vertical wind shear is the factor determining the placement of precipitation particles around the storm, while other factors determine the location, intensity, and means of their generation.

Climatology of overshootings in tropical cyclones and their roles in tropical cyclone intensity changes using TRMM data

“…For both RI initial and continuing storms (Figs. 3.6e,f), shallow precipitation peaks in the downshear-right quadrant, which is the quadrant where the triggering of convective updrafts begins, as indicated by previous studies (Black et al 2002;Hence andHouze 2011, 2012). As precipitation becomes deeper, the location of peak precipitation rotates cyclonically for RI storms.…”

Quadrant Distribution of Tropical Cyclone Inner-Core Kinematics in Relation to Environmental Shear

“…Two recent studies have used a large sample of storms to document the vertical structure of the tropical cyclone's inner core. Hence and Houze (2011) performed a statistical analysis of data obtained by the Tropical Rainfall Measurement Mission (TRMM) Precipitation Radar (PR) to investigate the vertical structure of hydrometeors in tropical cyclone eyewalls in relation to the large-scale shear. Their reflectivity distributions imply a systematic progression cyclonically from young convection in the downshear-right quadrant, to a mixture of mature convection and stratiform rain, to progressively more stratiform characteristics around the eyewall in the upshear quadrants.…”

Unusually rapid intensification of Typhoon Man-yi in 2013 under preexisting warm-water conditions near the Kuroshio front south of Japan

“…10g-i). Hence and Houze (2011) have confirmed that younger convection was present to the right of the downshear vector, whereas a multiscale statistical study of TRMM Precipitation Radar data indicated that there was a more mature mixture of intense convection and stratiform echo to the left of the downshear vector. Initiation of convection to the right of the downshear vector (Black et al 2002;Reasor et al 2013) and dissipation on the upshear side are consistent with the enhancement of the mesovortex simulated in the MIX2013 experiment.…”