Role of Mesoscale Convective Rings and Mesoscale Convective Blowouts in Tropical Cyclone Formations during TCS-08 Experiment

During the Tropical Cyclone Structure (TCS-08) field experiment, 16 ring-like mesoscale convective events developed and three of these led to Tropical Depression formations. The most dramatic of these events (termed mesoscale convective blowouts) were ring-like curved bands of more than 5° latitude diameter with radial outflow in all directions around a cloud-free area. A second unique aspect was the re-formation(s) of a convective cluster within the cloud-free area that eventually became the locus of the Tropical Depression (TD).

The focus of the presentation will be on the special environmental conditions that led to pre-TD14W, pre-TY Nuri, and pre-TY Hagupit. Upper-tropospheric atmospheric motion vectors from CIMMS reveal the radial outflows and the interaction with the impinging flow that sometimes constrains the outflow until the environment becomes more favorable for development. Comparison with 25 km resolution ECMWF analyses from the Year of the Tropical Convection archive reveal the three-dimensional structure of the synoptic environment of the mesoscale convective events.

The ECMWF analyses occasionally have point-source convective towers with strong outflow aloft in association with low-level circulation centers (e.g., with pre-Hagupit) or a reverse-oriented monsoon trough in the pre-14W case. However, these convective towers do not necessarily correspond with the locations and timing of the ring-like mesoscale convective blowout events until the environmental conditions have been modified by a previous convective event as in the case of pre-TY Nuri.