Quikscat-Derived Near-Surface Vorticity during Tropical Cyclogenesis

• Other Authors: Minter, Elizabeth (authoraut), Reasor, Paul D. (professor directing thesis), Bourassa, Mark A. (committee member), Cunningham, Philip (committee member), Department of Earth, Ocean and Atmospheric Sciences (degree granting department), Florida State University (degree granting institution)
• Format: Text
• Language: English
• Published: Florida State University
• Subjects: Meteorology; North Atlantic
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-2394; http://fsu.digital.flvc.org/islandora/object/fsu%3A180599/datastream/TN/view/Quikscat-Derived%20Near-Surface%20Vorticity%20during%20Tropical%20Cyclogenesis.jpg

Traditional surface and upper-air observations are often absent over the tropical oceans. This lack of routine in-situ measurement, outside of special field programs, has limited the observational study of tropical cyclogenesis. Remote sensing from satellites, however, can provide information in regions where surface-based observing networks are not present. This study utilizes infrared satellite imagery and QuikSCAT-derived near-surface vorticity from the 2005 hurricane season in the North Atlantic to examine the relationship between deep convection and low-level vorticity during tropical cyclogenesis. QuikSCAT-derived cyclonic relative vorticity is identified in association with developing easterly wave disturbances tracked using NHC products and 3-hourly infrared satellite imagery. Area-averaged vorticity near mesoscale regions of convection within the easterly wave envelope is then computed. In most of the 19 cases examined, the low-level vorticity followed the convective evolution, decreasing or remaining nearly constant during periods of inactive convection and increasing as convective activity increased. A composite of North Atlantic easterly wave disturbances was constructed to characterize the average evolution of near-surface vorticity during tropical cyclogenesis. 48 hours prior to genesis, the average tropical disturbance has a region of cyclonic relative vorticity about 125 km in diameter with peak magnitude of approximately 1x10-4 s-1. During its subsequent evolution, the vorticity of the composite disturbance increases as convection increases until a tropical cyclone forms. These results are considered in the context of prior and future numerical simulations of tropical cyclogenesis. A Thesis Submitted to the Department of Meteorology in Partial Fulfillment of the Requirements for the Degree of Master of Science. Spring Semester, 2007. December 8, 2006. Quikscat, Seawinds, Tropical Disturbance, Tropical Cyclogenesis, Vorticity Includes bibliographical references. Paul D. Reasor, Professor Directing Thesis; Mark A. Bourassa, Committee Member; Philip Cunningham, Committee Member.