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Abstract Secondary eyewall formation (SEF) in tropical cyclones (TCs) emerges from a complex interplay of internal dynamics and environmental influences. Motivated by observations linking low inertial stability in the TC outflow layer to eyewall replacement cycles, we investigate how variations in outflow‐layer inertial stability control both the initiation and radial position of SEF. Idealized simulations reveal that reduced outflow‐layer inertial stability enhances upper‐level divergence and updraft in the TC outer core, fostering the growth of stratiform rainbands. By averaging secondary circulation over the domain grids featuring stratiform precipitation, it is explicitly shown that the strength of the mesoscale descending inflow (MDI) is greater within the widespread and more developed stratiform clouds. Such stratiform‐induced MDI can dynamically and thermodynamically broaden the tangential wind field in the lower altitudes. As a result, the ensuing increase in boundary‐layer inertial stability and inflow supplies greater absolute vorticity influx in the outer‐core region, making the tangential wind tendency peaks and the secondary eyewall intensifies at a larger radius. This study highlights the role of MDI in the coupling between the upper‐ and lower‐tropospheric dynamics.
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This content will become publicly available on November 1, 2026
A Numerical Study on Hurricane Patricia (2015). Part II: The Topographic Effect and the Secondary Eyewall Formation
Abstract Hurricane Patricia (2015), the most powerful tropical cyclone (TC) on record, formed its secondary eyewall when its center was about 113 km offshore before its landfall at the southwestern coast of Mexico at around 2300 UTC 23 October. The ARW-WRF Model reproduced well the main features, allowing for a detailed investigation of the secondary eyewall formation (SEF). Our results show that the secondary eyewall developed from a stationary banding complex (SBC), originating from the intersection of two outer rainbands (OR1 and OR2) on the western side of the TC. This process was largely regulated and enhanced by the coastal terrain through the orographic channel effect. The results from sensitivity experiments show that increasing terrain height amplified the channel effect, accelerating airflow between the TC vortex and the terrain, strengthening convergence into OR1, and promoting midlevel descending inflow conducive to convective enhancement downstream in the SBC. While the terrain weakened low-level moisture transport, it also positioned OR2 closer to OR1, facilitating the formation of the SBC and accelerating the moat development. Backward trajectory analysis revealed that the inflows below the upper-level outflow layers of both the primary and secondary eyewalls contributed to moat development. With increasing terrain height, dry air transported into the moat region by the upper-level inflows from the secondary eyewall significantly increased, further suppressing convection in the moat. These findings offer novel insights into the understanding of SEF processes and underscore the importance of the topographic effects in shaping outer rainband organization, contributing to the moat and SEF.
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- Award ID(s):
- 1834300
- PAR ID:
- 10652991
- Publisher / Repository:
- AMS
- Date Published:
- Journal Name:
- Monthly Weather Review
- Volume:
- 153
- Issue:
- 11
- ISSN:
- 0027-0644
- Page Range / eLocation ID:
- 2375 to 2395
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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