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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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Examining Storm Asymmetries in Hurricane Irma (2017) Using Polarimetric Radar Observations
Abstract Dual‐polarization radar observations of Hurricane Irma (2017) provide new insight into the microphysical structure of a mature tropical cyclone that can be tied to the cyclone dynamics. The primary eyewall exhibited a radar signature of hydrometeor size sorting, which implied that large drops fell out near persistent upward motion in the front‐right quadrant of the storm, while smaller drops were advected downstream. In the outer rainbands, convective initiation was also preferred in the front‐right quadrant, whereas stratiform precipitation was predominant downwind. For both the primary eyewall and outer rainbands, the preferred quadrant for convective initiation was consistent with the expected kinematic asymmetry of a tropical cyclone in weak environmental wind shear but with moderate translation speed. The developing secondary eyewall exhibited a different asymmetry that indicated a stratiform‐to‐convective transition associated with heavy precipitation in the rear quadrants. This transition is consistent with hypothesized dynamical theories for secondary eyewall formation.
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- Award ID(s):
- 1810869
- PAR ID:
- 10375695
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 45
- Issue:
- 24
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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