Tropical Cyclone Distribution and Intensity Change in the Western Pacific Ocean
STATE UNIV OF NEW YORK AT ALBANY DEPT OF EARTH SCIENCES
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LONG-TERM GOALS. The long-term goals of this research are to understand the processes that determine the spatial and temporal distribution of tropical cyclones in the western Pacific Ocean. OBJECTIVES. The primary objectives during the last year have been to address why tropical cyclones tend to occur in clusters in the Western Pacific Ocean, i.e., two or more storms in the same region, followed by two or more in a completely different region. Our efforts have centered on the role of equatorial wave modes, especially mixed Rossby-gravity and n1 Equatorial Rossby ER waves. We are also trying to reconcile the monsoon trough-centered paradigm of tropical cyclone genesis with paradigm involving westward-moving waves interacting with slowly varying background features like the Madden-Julian Oscillation MJO. APPROACH. We believe the best way to address the questions above is with detailed synoptic case studies rather than composite or statistical studies. We make use of gridded analyses from ECMWF and of outgoing longwave radiation OLR data. Both data sets were filtered in time to isolate the slowly-varying background representative of the MJO and other slowly varying features from the time scale of waves and tropical cyclones. In addition, a shallow water model was developed by Anantha Aiyyer to give insight into how the MJO, mixed Rossby-gravity waves, and tropical cyclogenesis are related. The slowly-varying background with an active MJO was simulated by integrating to steady state with an imposed mass sink. Linear model simulations with small-amplitude disturbances were carried out with this background state assumed fixed. Analytically defined mixed Rossby gravity wave trains were generated and allowed to interact with the background state.