Abstract The dynamics of an asymmetric rainband complex leading into secondary eyewall formation (SEF) are examined in a simulation of Hurricane Matthew (2016), with particular focus on the tangential wind field evolution. Prior to SEF, the storm experiences an axisymmetric broadening of the tangential wind field as a stationary rainband complex in the downshear quadrants intensifies. The axisymmetric acceleration pattern that causes this broadening is an inward-descending structure of positive acceleration nearly 100 km wide in radial extent and maximizes in the low levels near 50 km radius. Vertical advection from convective updrafts in the downshear-right quadrant largely contributes to the low-level acceleration maximum, while the broader inward-descending pattern is due to horizontal advection within stratiform precipitation in the downshear-left quadrant. This broad slantwise pattern of positive acceleration is due to a mesoscale descending inflow (MDI) that is driven by midlevel cooling within the stratiform regions and draws absolute angular momentum inward. The MDI is further revealed by examining the irrotational component of the radial velocity, which shows the MDI extending downwind into the upshear-left quadrant. Here, the MDI connects with the boundary layer, where new convective updrafts are triggered along its inner edge; these new upshear-left updrafts are found to be important to the subsequent axisymmetrization of the low-level tangential wind maximum within the incipient secondary eyewall.
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Statistical Analysis of Convective Updrafts in Tropical Cyclone Rainbands Observed by Airborne Doppler Radar
Ten years of airborne Doppler radar observations are used to study convective updrafts' kinematic and reflectivity structures in tropical cyclone (TC) rainbands. An automated algorithm is developed to identify the strongest rainband updrafts across 12 hurricane‐strength TCs. The selected updrafts are then collectively analyzed by their frequency, radius, azimuthal location (relative to the 200–850 hPa environmental wind shear), structural characteristics, and secondary circulation (radial/vertical) flow pattern. Rainband updrafts become deeper and stronger with increasing radius. A wavenumber‐1 asymmetry arises, showing that in the downshear (upshear) quadrants of the TC, updrafts are more (less) frequent and deeper (shallower). In the downshear quadrants, updrafts primarily have in‐up‐out or in‐up‐in secondary circulation patterns. The in‐up‐out circulation is the most frequent pattern and has the deepest updraft and reflectivity tower. Upshear, the updrafts generally have out‐up‐in or in‐up‐in patterns. The radial flow of the updraft circulations largely follows the vortex‐scale radial flow shear‐induced asymmetry, being increased low‐level inflow (outflow) and midlevel outflow (inflow) in the downshear (upshear) quadrants. It is hypothesized that the convective‐scale circulations are significantly influenced by the vortex‐scale radial flow at the updraft base and top altitudes. Other processes of the convective life cycle, such as bottom‐up decay of aging convective updrafts due to increased low‐level downdrafts, can influence the base altitude and, thus, the base radial flow of the updraft circulation. The findings presented in this study support previous literature regarding convective‐scale patterns of organized rainband convection in a mature, sheared TC.
more » « less- Award ID(s):
- 1810869
- NSF-PAR ID:
- 10366923
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 127
- Issue:
- 6
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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