The Impact of Future Climate Change on TC Intensity and Structure: A Downscaling Approach

Abstract

A comprehensive analysis of tropical cyclone (TC) intensity change in a warming climate is undertaken with high-resolution (6- and 2-km grid spacing) idealized simulations using the Weather Research and Forecasting (WRF) model. With the goal of isolating the influence of thermodynamic aspects of climate change on maximum hurricane intensity, an idealized TC is placed within a quiescent, horizontally uniform tropical environment computed from averaged reanalysis data for the tropical Atlantic Ocean. The analyzed tropical environment is used for control simulations. Changes between the periods 1990–99 and 2090–99 are computed using output from 13 GCMs from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), for the A1B, A2, and B1 emissions scenarios. These changes are then added to the reanalysis-derived initial and boundary conditions used in the control simulations. Some processes known to impact TC intensity, such as environmental vertical wind shear and sea surface wake cooling, are not considered in this study. Future TC intensity increased for 75 of 78 future simulations using 6-km grid length, with a 9% (~8 hPa) average increase in central surface-pressure deficit. For the 2-km simulations, the average increase was 14% (~14 hPa). The depth of the TC secondary circulation increases in future simulations, consistent with an increase in the height of the freezing level and tropopause. Inner-core precipitation increases of 10%–30% are found for future simulations, with large sensitivity to the emission scenario. The increase in precipitation is consistent with a stronger potential vorticity tower, a warmer eye, and lower central pressure. Enhanced upper-tropospheric warming in the GCM environment is shown to be an important mitigating influence on TC intensity change but is also shown to exhibit large uncertainty in GCM projections.