Subtropical Cyclone Formation via Warm Seclusion Development: The Importance of Surface Fluxes

Subtropical cyclones (STCs) are characterized by a thermal hybrid structure with tropical and extratropical features. STCs are considered a numerical modeling challenge because of their rapid intensification. A fundamental part of their strength is derived from diabatic processes associated with con...

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Bibliographic Details
Published in:Journal of geophysical research. Atmospheres 2020-04, Vol.125 (8), p.n/a
Main Authors: Quitián‐Hernández, L., González‐Alemán, J. J., Santos‐Muñoz, D., Fernández‐González, S., Valero, F., Martín, M. L.
Format: Article
Language:English
Subjects:
Atmospheric models
Atmospheric motion
Computational fluid dynamics
Computer simulation
Convection
Cyclones
Frontogenesis
Geophysics
Heat
Heat flux
Heat transfer
Hybrid structures
Meridional flow
Potential vorticity
Rain
Rainfall
Surface fluxes
Tropical climate
Vectors
Vorticity
Weather forecasting
Wind
Wind analysis
Wind shear
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Summary:Subtropical cyclones (STCs) are characterized by a thermal hybrid structure with tropical and extratropical features. STCs are considered a numerical modeling challenge because of their rapid intensification. A fundamental part of their strength is derived from diabatic processes associated with convection and heat fluxes from the ocean. This study evaluates the importance of surface turbulent heat fluxes during the transition of an extratropical precursor into a STC. This cyclone evolved embedded within a strong meridional flow, having a Shapiro‐Keyser structure and undergoing a warm seclusion process. To assess the importance of those heat fluxes, two Weather Research and Forecasting simulations were defined considering the presence and absence of those fluxes. Results of both simulations reveal a warm seclusion process, which weakened in absence of the heat fluxes. During the system genesis and in absence of heat fluxes, the wind and rainfall values were increased due to the remarkably intense area of frontogenesis to the northwest. Given these results and the lack of transition in the absence of heat fluxes, the frontal nature of the system was verified. Considering the heat fluxes, the obtained potential vorticity values diminished, reducing wind shear and intensifying convection in the system, which favored its transition into an STC. This study is groundbreaking in that no STC has been linked to a warm seclusion process in the Eastern North Atlantic. Additionally, simulated wind field shows an underestimation in comparison with Atmospheric Motion Vectors, used as observational data so as to give a weight to the wind analysis. Key Points Observed warm seclusion process of a Shapiro‐Keyser‐like subtropical cyclone Surface turbulent heat fluxes played a key role during intensification of the cyclone No transition into a subtropical cyclone is found in absence of surface turbulent heat fluxes
ISSN:2169-897X
2169-8996
DOI:10.1029/2019JD031526