Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Department

Geosciences

First Advisor's Name

Haiyan Jiang

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Hugh Willoughby

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Ping Zhu

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Robert Burgman

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Wei Wang

Fifth Advisor's Committee Title

Committee member

Keywords

Tropical cyclones, Hurricanes, surface winds, composite analysis, satellite observations

Date of Defense

3-30-2017

Abstract

Surface wind speeds are an important and revealing component of the structure of tropical cyclones (TCs). To understand the asymmetric structure of surface winds in TCs associated with differences in formation region, environmental wind shear, storm forward motion, and TC strength and intensification, a twelve year database of satellite scatterometer data are utilized to produce composite total wind speed and Fourier-derived, low wavenumber analyses. A quantified asymmetry is determined as a function of TC intensity and reveals the tropical storms are influenced by wind shear at all TC-centric radii but only for areas away from the radius of maximum wind in hurricanes. Additionally, an increase of absolute angular momentum flux has a preference for the downshear-right quadrant, and the low wavenumber maximum develops downwind of this momentum transport. Further evaluation of the asymmetric structure with respect to wind shear’s relation to motion and impacts during TC intensity change are also considered.

A composite rapid intensification event is produced and compared to overlapping satellite rain estimates. Results indicate that the TC becomes more symmetric during intensification and the phase of the maximum asymmetry rotates from a downshear-left direction to upshear-left direction after the intensification slows. The rain or convective maximum is generally located upwind of the surface wind maximum at the early stages of intensification and is coincident with the region of large angular momentum transport, which supports the idea that the surface wind asymmetry is likely a consequence of convective or other processes. Using data from a regional TC model, it is also determined that the scatterometer data are useful for model verification of tropical storms and non-major hurricanes and performs similar to or better than the standard tool at forecast lead times up to 60 hours. Preliminary comparisons of model-derived surface wind asymmetry relative to rain generally confirm the observational results.

Identifier

FIDC001738

ORCID

0000-0002-6061-6531

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