Potential Vorticity Diagnostics of Hurricane Movement. Part II: Tropical Storm Ana (1991) and Hurricane Andrew (1992)

Abstract

The validity of balance dynamics in the Tropics allows an exploration of the dynamics of hurricanes using the potential vorticity (PV) framework. Part I demonstrated the use of PV diagnostics in understanding the hurricane steering flow and also the interaction between the cyclone and its environment. To obtain a broader understanding of this PV methodology, two other observational case studies are performed (Tropical Storm Ana of 1991 and Hurricane Andrew of 1992) emphasizing the same methods of analysis. The results are consistent with a previous finding that the hurricane advection flow, defined by inverting the entire PV distribution excluding the storm's own positive anomaly, is a good approximation to real cyclone movement, even though the original data cannot capture the actual hurricane strength. This study confirms that upper-level PV anomalies can play an important role in the motion of the storm. But their quantitative effect on the cyclone's motion depends strongly on the relative location of the vortex and the upper-air PV features. Due to the limitations of the data, the ? effect or the mechanism proposed by Wu and Emanuel was not able to be supported or disproved.