Fewer total number of hurricanes but more intense ones in a warmer world
The four idealized configurations of the US CLIVAR Hurricane Working Group are integrated using the global Community Atmospheric Model version 5.1 at two different horizontal resolutions, approximately 100km and 25km. The publicly released 0.9ox1.3o configuration is a poor predictor of the sign of the 0.23ox0.31o model configuration’s change in the total number of tropical storms in a warmer climate. However, it does predict the sign of the higher resolution configuration’s change in the number of intense tropical cyclones in a warmer climate. In the 0.23ox0.31o model configuration, both increased CO2 concentrations and elevated sea surface temperature (SST) independently lower the number of weak tropical storms and shorten their average duration. Conversely, increased SST causes more intense tropical cyclones and lengthens their average duration resulting in a greater number of intense tropical cyclone days globally. Increased SST also increased maximum tropical storm instantaneous precipitation rates across all storm intensities. We find that while a measure of maximum potential intensity based on climatological mean quantities adequately predicts the 0.23ox0.31o model’s forced response in its most intense simulated tropical cyclones, a related measure of cyclogenesis potential fails to predict the model’s actual cyclogenesis response to warmer SSTs. These analyses lead to two broader conclusions: 1) Projections of future tropical storm activity obtained by a direct tracking of tropical storms simulated by CMIP5-class resolution climate models must be interpreted with caution. 2) Projections of future tropical cyclogenesis obtained from metrics of model behavior that are based solely on changes in long-term climatological fields and tuned to historical records must also be interpreted with caution.
Citation: Michael Wehner, Prabhat, Kevin Reed, Daithi Stone, William D. Collins, Julio Bacmeister, Andrew Gettleman (2014) Resolution dependence of future tropical cyclone projections of CAM5.1 in the US CLIVAR Hurricane Working Group idealized configurations. J. Climate 28, 3905-3925. DOI: 10.1175/JCLI-D-14-00311.1