Tropical Cyclones and Associated Environmental Fields in CMIP6 Models

Abstract

Abstract The authors analyze the environmental fields associated with tropical cyclone (TC) activity in phase 6 of the Coupled Model Intercomparison Project (CMIP6) models, as well as the TC-like storms in those models. First, the model biases in the historical climatological means of chosen environmental fields are evaluated against the fifth generation of the European Centre for Medium-Range Weather Forecasts (ECMWF) global atmospheric reanalysis (ERA5). Second, we show that the interannual variability of these fields is typically much smaller in models than in reanalysis. Applying a mean bias correction to these fields before calculating tropical cyclone genesis indices improves the variability of the modeled indices compared to those in reanalysis, as well as the means, due to the nonlinear dependence of the indices on these fields. The authors consider how these environmental fields change in the CMIP6 models, using three future scenarios separately as well as combining scenarios and times according to specific greenhouse warming levels. Multiple proxies for TC activity are considered, and we show that the signs of the future changes are dependent on the choice of genesis index. The relationship between climate sensitivity and potential intensity change across the multimodel ensemble is examined. The statistics of the TC-like structures in the historical simulations are also examined, using the number of TCs (NTC) and accumulated cyclone energy (ACE) as diagnostics, including calculations of the percentage changes in NTC and ACE at the end of 21C as compared with 20C. Large decreases in both of these quantities are found in the highest emission scenario.

Topics & Concepts