Circulation Dynamics of Pre-depression Karl (2010) Observed During PREDICT

The Pre-Depression Investigation of Cloud-systems in the Tropics (PREDICT) experiment was sponsored by the National Science Foundation as part of a tri-agency field campaign to explore the multi-scale dynamic and thermodynamic interactions that lead to tropical cyclogenesis. Recent studies have indicated that a protected, quasi-closed Lagrangian recirculation region inside a parent synoptic scale disturbance provides a favorable environment for the formation of a tropical cyclone. Results from the TPARC/TCS08 and the PREDICT experiments suggest that the persistence of a relatively deep and strong recirculation region on the meso-alpha scale, or “pouch”, is a very favorable condition for tropical cyclogenesis in the real atmosphere. At the smaller horizontal scales, aggregation of convectively amplified cyclonic vorticity in the lower troposphere and the corresponding system-scale influx of cyclonic vorticity has been suggested to be the primary upscale growth mechanism for the emergent tropical cyclone.

This talk will examine these hypotheses using observations of pre-depression Karl by multiple aircraft as part of NSF PREDICT, NASA GRIP, and NOAA IFEX. Analyses following the meso-alpha scale recirculation region indicate alternating periods of low and mid-level spin-up associated with repeated bursts of rotating deep convection on the meso-gamma scale. Satellite and Doppler radar data suggest that convective and stratiform precipitation processes are primarily associated with low and mid-level spin-up periods respectively, but that both are playing an important role in Karl's intensification. Dropsonde observations suggest a strong coupling of the vorticity and moisture fields, pointing to a potential feedback between the circulation dynamics at different vertical levels and convective activity within the recirculation region. Similarities with analyses from the recent TPARC/TCS08 field campaign in the Western Pacific will be discussed briefly also in order to consider the possible universality of mesoscale processes leading to cyclogenesis.