12A.3 An investigation of tropical cyclogenesis using QuikSCAT vector winds (2008

12A.3

An investigation of tropical cyclogenesis using QuikSCAT vector winds

Elizabeth M. Minter, Florida State University, Tallahassee, Florida; and P. D. Reasor and M. A. Bourassa

QuikSCAT vector winds and infrared satellite imagery are used to examine

the pre-depression evolution of easterly waves in the North Atlantic

during the 1999-2006 hurricane seasons. Each pre-depression disturbance

is characterized by its absolute circulation within 125 km of the center

and by the percent area covered by convective clouds within 250 km. In

some cases positive and negative changes in convective organization are

reflected in the near-surface absolute circulation. In a composite

analysis of 50 developing cases it is found that an increase in absolute

circulation during the 72 hrs preceding NHC-classified depression stage

coincides with an increase in convective activity during the same period.

Average structure of the developing disturbance at different times

relative to depression stage will be presented. Following previous

studies of easterly wave development, the QuikSCAT data is used to

estimate the low-level detrained volume flux and budget absolute

circulation tendency. Relationships between these quantities, the

observed circulation, convective activity, and vertical shear are examined

on a case-by-case basis and for the composite disturbance.