The role of multiple mesoscale convective systems in a non-developing tropical disturbance observed during the Tropical Cyclone Structure-2008 (TCS-08) field experiment

Determining the path(s) by which a tropical disturbance transitions into a self-sustaining tropical cyclone remains an active area of research. Observational and numerical modeling studies have helped improve our understanding of the physical processes prior to and during tropical cyclogenesis. However, the majority of these studies have focused almost exclusively on developing systems, placing relatively little emphasis towards describing why, more often then not, tropical disturbances within seemingly favorable large-scale conditions fail to develop.

During the Tropical Cyclone Structure-2008 (TCS-08) field program over the western North Pacific, tropical cloud clusters that were potential precursors to tropical cyclone formation were identified. Over the two-month period of the field program, approximately 50 such systems were tracked. In this paper, the lifecycle of one of the non-developing systems that was labeled TCS025 is examined.

Throughout the evolution of TCS025, multiple mesoscale convective systems (MCSs) were observed to form in a region between two upper-level cold low-pressure centers. Over a period of three days, TCS025 was investigated by the U.S. Air Force WC-130J aircraft and the Naval Research Laboratory (NRL) P-3 aircraft. Observations were made by dropsonde measurements from both aircraft and by the Elecrta Doppler Radar (ELDORA) on the NRL P-3. Based on the in situ measurements, several mesoscale circulation centers were identified to correspond with the regions of MCS activity. However, further organization of the convection and circulation centers did not occur. This may have been due to several factors that caused the individual MCSs to propagate away from their region of origin, which prevented consistent generation of vorticity around which a low-level circulation might have organized.

The Advanced Weather Research and Forecasting numerical model (WRF-ARW) is used to examine the roles that MCS development had in the formation of the mesoscale circulations identified in observations. Based on the model simulations, factors that prevented the organization of TCS025 are examined in relation to interactions among synoptic-scale, disturbance-scale, and mesoscale influences.