Dr. Hazelton presented a seminar on “Convective Burst Development and Evolution in Two Simulated Atlantic TCs”.
Understanding the structure and evolution of the tropical cyclone (TC) inner core remains an elusive challenge in tropical meteorology, especially transient asymmetric features such as localized strong updrafts known as convective bursts (CBs). This study investigates the formation of CBs and their role in TC structure and evolution using high-resolution simulations of two hurricanes (Dean 2007 and Bill 2009) with the Weather Research and Forecasting (WRF) model.
Several different aspects of the dynamics and thermodynamics of the TC inner-core region are investigated with respect to their influence on TC convective burst development. Radius-height composites with CBs show stronger radial inflow in the lowest 2 km, and stronger radial outflow from the eye to the eyewall around z = 2-4 km, than composites without CBs. Asymmetric vorticity associated with eyewall mesovortices appears to be a major factor in leading to some of the radial flow anomalies that lead to CB development. Analysis of individual CBs and parcel trajectories show that many parcels are pulled into the eye, move outward into the eyewall, and rapidly ascend in CBs. The positive buoyancy observed along the parcel paths support the importance of eye-eyewall exchange in CB development.
Analysis of intensity change in the simulations shows that there are more inner-core CBs during times when the TCs are intensifying, while weakening/steady times appear to be associated with more CBs outside the radius of maximum wind (RMW), consistent with observational studies and theoretical work. However, times when the TC has already been intensifying and continues to do so have more CBs than times when the TC has been weakening but then intensifies. This result suggests that CB development may not always be predictive of intensification, but rather may occur as a result of ongoing intensification. Rapid intensification (RI) in the simulations is found to be associated with an even higher density of CBs inside the RMW than slower intensification. Lag correlations between CBs and intensity reveal a broad peak in correlation, with the CBs leading pressure falls by 0-3 hours. These results confirm the notion that convective heating inside the RMW (where inertial stability is higher) is favorable for intensification. However, it is shown that the relationship can vary in different cases depending on environmental conditions and the previous evolution of the TC.
A recording of the presentation is available on the anonymous ftp site: