Exploring the Relationship between Tropical Cyclogenesis and Kelvin Waves with MPAS-Aquaplanet Simulations

Abstract:

Four decades ago, Dr. Bill Gray noticed that tropical cyclones form in clusters followed by several weeks of inactivity. This pattern has recently re-gained attention with the growing interest in subseasonal-to-seasonal prediction of high-impact weather. Research in this area has uncovered that convectively coupled equatorial waves (CCEWs), in particular Kelvin waves, can partly explain week-to-week tropical cyclone activity through modulations of environmental conditions. However, the physical processes behind that relationship remain unexplored in part due to a lack of consistent datasets that capture the mesoscale and convective-scale processes that are ultimately necessary for tropical cyclogenesis. This limitation motivates this study, which aims at exploring if and how CCEWs modulate tropical cyclogenesis in idealized experiments on a water-covered sphere (“aquaplanet”). Idealized experiments with varying horizontal grid spacings—from 120-km to 3-km—were produced with the Model for Prediction Across Scales (MPAS). The experiments capture both Kelvin waves and tropical cyclones. A time-lagged analysis of cyclogenesis with respect to Kelvin wave passage confirms that a relationship exists between CCEWs and tropical cyclogenesis, but the relationship is different from that identified in previous studies and it depends on the horizontal grid spacing of the simulations. This presentation will discuss those results, along with an analysis of physical processes governing the relationship and the differences between experiments with varying horizontal grid spacing.