Abstract
The key to increasing confidence in future projections of tropical cyclone (TC) activity is understanding the large-scale environment in which TCs may form and intensify. In the deep tropics, the combined effect of potential intensity (PI), vertical wind shear (VWS), and the saturation deficit provides robust a physical connection between the large-scale environment and TC activity. In this work, the temperature profile near the tropopause is identified as leading to a large range of climatological PI values within global climate models (GCMs), even when sea surface temperatures (SSTs) are held constant across the GCMs. This dissertation also establishes the Matrix of Environments (MoE), which captures a spectrum of environments defined by PI and ventilation. Ventilation is the combined effect of VWS and the saturation deficit. Within each MoE environment, high-resolution ensemble simulations provide a measure of TC favorability. The Tropical Cyclone Environments Matrix Proxy (TC-EMP), which combines the favorability of individual MoE environments with their annual frequency, is derived and shown to be a skillful proxy of annual TC activity. When assessing the individual contributions of PI and ventilation to the interannual variability of TC activity, neither PI nor ventilation alone fully explain the interannual variance. It is also shown that the El Niño-Southern Oscillation (ENSO) has a more significant influence on PI in the tropical Atlantic than previously known, in addition to the well-established influence on ventilation. The TC-EMP is applied to a much longer time period, ranging from 1850 through 2100, using GCM simulations of historical and future climates. There is considerable agreement on an increase in the TC-EMP through 2100, implying more frequently favorable environmental conditions for TCs with future climate change. There is more uncertainty in the trend of ventilation than PI, due to notable uncertainty in future projections of VWS.