The Role of Deep Convection in Moistening the Inner Core Regions of Developing Tropical Cyclones: Evidence from GRIP 2010

On the meso-convective scale, deep convection is invariably identified as a requirement for tropical cyclogenesis. A fundamental question in tropical cyclogenesis is what environmental conditions, at multiple scales, are necessary for deep convection to organize intense low-level rotation? Critical to answering this question is characterizing the time evolution of not only the relevant vortices at low-levels, but also the associated convective systems and the thermodynamic state of the environment. In response to the need for a more extensive dataset on developing disturbances, NASA took part in a tri-agency field effort during August-September 2010. The NASA Genesis and Rapid Intensification Processes (GRIP) campaign, conducted concurrently with the NOAA Intensity Forecast Experiment (IFEX) and the NSF/NCAR Pre-depression Investigation of Cloud Systems in the Tropics (PREDICT) campaign, provides an unprecedented collaboration on tropical cyclogenesis events. Observing strategies involved consecutive and coordinated aircraft missions into developing disturbances. One event, Hurricane Karl, was investigated from its easterly wave phase (4 days prior to genesis) through genesis, first landfall in the Yucatan, rapid intensification to category 3 in the Gulf, and second landfall near Veracruz, Mexico. Tri-agency aircraft also extensively investigated another disturbance in the days before its genesis as Tropical Storm Matthew. This research combines in-situ data obtained from tri-agency aircraft into pre-Karl and pre-Matthew with the numerous passive microwave overpasses and conventional IR data to examine how convective events may modify the thermodynamic environment of the developing system. Using the wealth of high temporal and spatial resolution data available, the goal is to identify the characteristics and evolution of convective systems, the associated wind field, and the resulting thermodynamic modifications, and offer insight into what ultimately determines the fate of the disturbance.

To achieve a detailed history of convective events, areal coverage of precipitation and cold cloud, as well as convective intensity, is garnered from a synthesis of information from 30-min geosynchronous IR brightness temperatures and all available snapshots of 85- and 89 GHz brightness temperatures from microwave radiometers on AMSR-E, TRMM, and SSMI-I/S. Thermodynamic changes are quantified through total precipitable water derived from those same microwave sensors and dropsondes, relative humidity from in-situ data and AIRS, and (equivalent) potential temperature from dropsondes. Dropsondes also offer detailed information on the low and mid level wind fields. Relative vorticity is analyzed in both the earth-relative and co-moving (pouch) frameworks. Through a detailed analysis of the time evolution of convective events and the thermodynamic state of the environment, the role of deep convection in the progressive moistening (priming) of the inner core before genesis, as well as the hypothesis for near saturation through the troposphere as a necessary condition for genesis, is addressed.