The Genesis of Tropical Storm Matthew (2010) as Observed during the PRE-Depression Investigation of Cloud Systems in the Tropics (PREDICT) Field Experiment

The genesis sequence of Tropical Storm Matthew (2010) was observed over four consecutive days (20-23 Sep) by research aircraft from three agencies: i) the National Science Foundation GulfStream V (G-V) operated by the National Center for Atmospheric Research; ii) The National Aeronautics and Space Administration DC-8; and iii) the National Oceanic and Atmospheric Administration G-IV. One of the findings of this research is that due to overflight restrictions, the pre-Matthew disturbance was spatially under-sampled during three of the six research flights. Therefore, ECMWF analysis and geostationary satellite data are necessary to supplement these aircraft observations if a complete picture of the tropical cyclogenesis sequence is to be constructed. In this presentation the combined data set is used to distinguish between the dynamic and thermodynamic mechanisms that are critical to tropical cyclone formation versus those mechanisms that are merely incidental. First, vertical alignment of the vortex is the key factor leading to deep layer spin-up of the vortex. It is noted that the mechanism for vertical alignment does not appear to be tied to a relaxation of the vertical wind shear, as the deep layer (850-200 hPa) shear increases as genesis nears. Conversely, thermal stabilization (which has been hypothesized to lead to low-level vortex spin-up) does not have a pronounced impact on low-level spin-up of the pre-Matthew disturbance. Second, repeated bursts of convection near the center of the disturbance have the effects of moistening the environment and concentrating low-level vorticity. Third, there appears to be sufficient convective available potential energy (CAPE), coupled with reduced convective inhibition (CIN), within the pre-Matthew disturbance to support vigorous updrafts throughout the cyclogenesis sequence. Changes in the magnitude of CAPE appear to be tied to the evolution of convection and the time scale in which it takes the boundary layer to recover after an episode of vigorous convection, rather than spatial distances from the center of the disturbance or time preceding genesis.