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Abstract Hurricane Patricia (2015) formed over the eastern North Pacific and is the most intense tropical cyclone (TC) on record with a maximum sustained wind speed of 95 m s−1, which presented a great forecasting challenge due to its unprecedented rapid intensification, record-breaking lifetime maximum intensity, and subsequent rapid weakening. The intensity and structure changes in Patricia were successfully simulated in a control experiment using a two-way interactive, quadruply nested version of the Weather Research and Forecasting Model with both initial and lateral boundary conditions from the Global Forecast System Final Analysis data. The successful simulation resulted from the inclusion of dissipative heating, realistic horizontal mixing length, and sea-spray-mediated heat flux. The relative contributions of these processes were assessed based on a series of ensemble-based sensitivity experiments and energetic diagnostics. Results show that dissipative heating and reduced horizontal mixing length had the most significant impacts on the intensification rate of Patricia after it reached an intensity of category 3, contributing 25.8% and 28.9% to the intensification rate and 11.7% and 14.1% to the lifetime maximum intensity, respectively. The contribution by spray-mediated heat flux increased significantly with wind speed, contributing up to 20.1% to the intensification rate and 20% to the surface energy flux under the eyewall at the wind speed of 90 m s−1. An alternative surface drag coefficient scheme and a constant surface roughness for moisture and heat were also tested and discussed via sensitivity experiments. The study provides insights into the physical processes key to successful simulations and forecasts of extremely strong TCs.
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This content will become publicly available on July 16, 2026
The Wind‐Dependent Surface Drag Coefficient Contributes to the Secondary Eyewall Formation in Tropical Cyclones: A Case Study of Typhoon Gaemi (2024)
Abstract This study explores how a wind‐dependent surface drag coefficient (CD) influences secondary eyewall formation in tropical cyclones (TCs), using Super Typhoon Gaemi (2024) as a case study. We employ the Weather Research and Forecasting model with two different CDparameterizations and find that changing CDmarkedly affects boundary‐layer convergence and outer rainband evolution. In particular, the latest CDscheme with larger surface drag coefficient at wind speeds less than 45 m s−1yields higher surface stress and stronger boundary‐layer convergence in the outer core, thereby enhancing rainband convection and triggering earlier formation of a more coherent secondary eyewall structure compared to the scheme with smaller, nearly constant CDat wind speeds greater than 45 m s−1. These findings underscore the fundamental role of surface friction in shaping TC structure, with direct implications for operational TC forecasting, especially during eyewall replacement cycles.
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- Award ID(s):
- 1834300
- PAR ID:
- 10652990
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 13
- ISSN:
- 0094-8276
- Page Range / eLocation ID:
- e2025GL117521
- Subject(s) / Keyword(s):
- Tropical cyclones, secondary eyewall, surface drag coefficient, surface wind stress
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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