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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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Characteristics of Tropical Cyclone Outer Size and Structure Associated With Extratropical Transition
Abstract There is a lack of consensus on how tropical cyclone outer winds may change, if at all, due to extratropical transition. Hence, this study examines changes in North Atlantic tropical cyclone outer size and structure using a large, multidecadal sample of cases from reanalysis data. These results suggest that tropical cyclone outer size and structure typically remain unchanged until after extratropical transition end. In those minority of cases with strong expansion during extratropical transition, increases in tropical cyclone outer winds begin first in the lower troposphere during extratropical transition and build upwards over time. This broadening of the azimuthal‐mean outer winds is also associated with an increasingly asymmetric outer wind field with the strongest winds concentrated downstream of the tropical cyclone. These storms that expand most strongly during transition are typically smaller at transition start and eventually become embedded in more strongly baroclinic environments by extratropical transition end.
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- Award ID(s):
- 2028151
- PAR ID:
- 10577000
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 5
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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