Simulation of the Global ENSO-Tropical Cyclone Teleconnection by a High-Resolution Coupled General Circulation Model

This study presents an assessment of how global tropical cyclone activity is influenced by the El Nino Southern Oscillation (ENSO) using a long 150-year integration with a high resolution coupled atmosphere-ocean general circulation model (HiGEM; with N144 resolution, ~ 90 km in the atmosphere and ~ 40 km in the ocean). The results are compared to an atmosphere-only Atmospheric Model Intercomparion Project (AMIP) simulation using the atmospheric component of HiGEM (HiGAM). Observations of tropical cyclones in the International Best Track Archive for Climate Stewardship (IBTrACS) and applying a feature tracking algorithm to ERA-Interim data are used to validate the models. Composites anomalies of El Nino and La Nina years are used to identify a robust response. HiGEM is able to capture the shift of tropical cyclone location in the Pacific and Indian Ocean. However, HiGEM does not capture the expected ENSO-tropical cyclone teleconnection in the North Atlantic. HiGAM shows more skill in simulating the global ENSO-tropical cyclone teleconnection although over pronounces the variability in the Pacific. HiGAM is able to capture the ENSO-tropical cyclone teleconnection in the North Atlantic more accurately than HiGEM. An investigation into the large-scale environmental conditions, known to influence tropical cyclone activity is used to determine the response of tropical cyclone activity to ENSO in the North Atlantic and Western North Pacific. The ascending region of the Walker circulation during El Nino in HiGEM is constrained to a narrow region in the Western Pacific. This limits the upper-level westerlies extending to the Caribbean Sea and the vertical wind shear response is not captured. HiGAM simulates the expected mid-level relative humidy variability with ENSO in the Western North Pacific and gives a more realistic representation of the tropical cyclone activity than HiGEM.