Details:

Journal Title:
Journal of the Atmospheric Sciences
Personal Author:
Rios-Berrios, R. ; Davis, C. A. ; Torn, R. D.
Rios-Berrios, R. ; Davis, C. A. ; Torn, R. D. Less -
NOAA Program & Office:
OAR (Oceanic and Atmospheric Research) ; NWS (National Weather Service)
OAR (Oceanic and Atmospheric Research) ; NWS (National Weather Service) Less -
Description:
A major open issue in tropical meteorology is how and why some tropical cyclones intensify under moderate vertical wind shear. This study tackles that issue by diagnosing physical processes of tropical cyclone intensification in a moderately sheared environment using a 20-member ensemble of idealized simulations. Consistent with previous studies, the ensemble shows that the onset of intensification largely depends on the timing of vortex tilt reduction and symmetrization of precipitation. A new contribution of this work is a process-based analysis following a shear-induced midtropospheric vortex with its associated precipitation. This analysis shows that tilt reduction and symmetrization precede intensification because those processes are associated with a substantial increase in near-surface vertical mass fluxes and equivalent potential temperature. A vorticity budget demonstrates that the increased near-surface vertical mass fluxes aid intensification via near-surface stretching of absolute vorticity and free-tropospheric tilting of horizontal vorticity. Importantly, tilt reduction happens because of a vortex merger process—not because of advective vortex alignment—that yields a single closed circulation over a deep layer. Vortex merger only happens after the midtropospheric vortex reaches upshear left, where the flow configuration favors near-surface vortex stretching, deep updrafts, and a substantial reduction of low-entropy fluxes. These results lead to the hypothesis that intensification under moderate shear happens if and when a “restructuring” process is completed, after which a closed circulation favors persistent vorticity spinup and recirculating warm, moist air parcels.
Keywords:
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Cyclones Precipitation Wind Shear
Source:
Journal of the Atmospheric Sciences, 75(12), 4149-4173
DOI:
https://doi.org/10.1175/jas-d-18-0070.1
Document Type:
Journal Article
Funding:
Grant no. NA14OAR4830172 ; Grant no. NA16NWS4680025
Grant no. NA14OAR4830172 ; Grant no. NA16NWS4680025 Less -
Rights Information:
Other
Compliance:
CHORUS
Main Document Checksum:
[+]
urn:sha256:9e37e6b8ac736babf2501b2601d83f8b0df66ab51a4677ee37cddcf09a868f3f
Download URL:
https://repository.library.noaa.gov/view/noaa/48353/noaa_48353_DS1.pdf
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