LONG-TERM GOALS

The long-term goals of our research are to understand the interactions between tropical cyclones and their surroundings, and how such interactions influence tropical cyclone structure and intensity. OBJECTIVES The primary objective of this proposal was to understand the interactions of upper tropospheric potential vorticity centers and tropical cyclones, and to develop a "path to operations " that will allow prediction of tropical cyclone intensity change during such interactions. This objective is an extension of our previous ONR-funded work. The second objective was to understand the mechanisms behind the clustering of tropical cyclone occurrence in time, with the ultimate goal of predicting the presence of multiple tropical cyclones in advance. This represents a new initiative. Early studies have been for the eastern Pacific Ocean, but are now being extended to the western Pacific. APPROACH The first objective has been approached by observational studies using gridded analyses from the European Centre for Medium Range Weather Forecasting, and by numerical simulations of the tropical cyclone outflow layer during trough interactions. Individual case studies have been successful in the past. We are now carrying out broader studies of multiple storms in the Atlantic Basin over a 12-year period in order to define the range of behaviors of tropical cyclones during trough interactions, and to develop methods for intensity prediction during such episodes. The second objective has made use of gridded analyses from ECMWF and gridded analyses of outgoing longwave radiation (OLR). Both have been low-pass and band-pass filtered where appropriate