Resolution Sensitivity of Tropical Cyclone Genesis and Life Cycle in a Global Climate Model

We evaluate the impact of model resolution on the simulated variability of tropical cyclone (TC) genesis and lifecycle over the tropical North Atlantic. We analyze control and historical simulation ensembles of low-resolution (one degree) and high-resolution (quarter degree) atmosphere-only and fully coupled Energy Exascale Earth System Model (E3SM v0.4). This study evaluates the variability of large-scale environmental characteristics that are believed to significantly influence tropical cyclones, namely, absolute and relative SSTs, vertical shear, African easterly waves and dust loading over the tropical Atlantic and the main development region (MDR) along with explicit metrics of tropical cyclone variability. We also compare E3SM’s ability at the two resolutions to reproduce the influence of large scale modes of climate variability - El Niño–Southern Oscillation (ENSO), Atlantic Meridional Oscillation (AMO) on the coupled responses of these environmental controllers of TC genesis in the North Atlantic. Preliminary analysis of a four-member atmosphere-only simulation ensembles prescribed with observed SSTs and sea-ice conditions over the 1979-2005 period indicates that the high-resolution model simulates a weaker strengthening of vertical shear over the MDR during El-Nino events as compared to the low-resolution model and observations. This suggests a weaker than observed suppression (enhancement) of tropical cyclone activity during El Nino (La Nina) years in the high-resolution model. We will also present a study of the underlying mechanistics resulting in the noted model behavior.