Thermodynamic Climate Change and its Influence on Tropical Cyclone Intensity

The effects of changes in thermodynamic environments in the western North Pacific (WNP) on tropical cyclone (TC) intensity are investigated. Reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) are used to examine changes in thermodynamic environments during 1979-2012, in terms of the temperature, specific humidity, and sea-surface temperature (SST). In the primary TC genesis region in WNP, the temperature in the mid- and lower troposphere generally increased with time, and a significant cooling trend in the upper troposphere and lower stratosphere (UTLS) region was present. The specific humidity increased below 500 hPa, while there was a decreasing tendency between 300 and 500 hPa. SST in WNP was generally increased due to global warming. The maximum potential intensity (MPI) calculated from the three thermodynamic variables also shows an increasing trend during 1979-2012. By using the profiles of three thermodynamic variables, which are averaged over WNP in each year, as initial conditions of numerical simulation, thirty-four different idealized experiments are conducted using the Weather Research and Forecasting (WRF) model. Simulation results indicate that the intensity of TC with more recent year's thermodynamic environmenst is stronger as predicted by MPI. Through additional experiments, relative contributions of the three thermodynamic variables to changes in TC intensity are examined. We found that the changes in individual thermodynamic variable lead to intensified TC, and that the changes in the combined three variables contribute to the TC intensification more than the sum of the contirbution by individual variable.