Thermodynamic Environments of Deep Convection in Atlantic Tropical Disturbances

Conditional composites of dropsondes deployed into eight tropical Atlantic weather systems during 2010 are analyzed. The samples are conditioned based on cloud-top temperature within 10 km of the dropsonde, the radius from the cyclonic circulation center of the disturbance, and the stage of system development toward tropical cyclogenesis. Statistical tests are performed to identify significant differences between composite profiles. Cold-cloud-region-composite profiles of virtual temperature deviations from a large-scale instantaneous average indicate enhanced static stability prior to genesis within 200 km of the center of circulation, with negative anomalies below 700 hPa and larger warm anomalies above 600 hPa. Moist static energy is enhanced in the middle troposphere in this composite mainly because of an increase in water vapor content. Prior to genesis the buoyancy of lifted parcels within 200 km of the circulation center is sharply reduced compared to the buoyancy of parcels farther from the center. These thermodynamic characteristics support the conceptual model of an altered mass flux profile prior to genesis that strongly favors convergence in the lower troposphere and rapid increase of circulation near the surface. It is also noted that the air-sea temperature difference is greatest in the inner core of the pregenesis composite, which suggests a means to preferentially initiate new convection in the inner core where the rotation is greatest.