Effects of Cumulus Parameterizations and Radiation Schemes on Tropical Cyclone Frequency and Structure

This study focuses on the effects of two different cumulus parameterizations and two different radiation schemes on tropical cyclone frequency and structure in a coupled global climate model, the Florida State University Coupled Global Spectral Model. The model, run at resolution T63, simulates the global climate for 90 days initialized at 12Z on July 29 for each of the years analyzed. The FSUCGSM allows for a choice of two physical parameterizations: cumulus parameterizations and radiation schemes. The two cumulus parameterizations are a modified Kuo scheme and a modified Arakawa-Schubert scheme. The two radiation schemes are the absorptivity-emissivity model and the band model. Using objectively defined model- and basin-dependent thresholds will allow for the detection and analysis of tropical cyclones in each configuration of the model. For each configuration of the model, two tropical cyclones are selected from all the tropical cyclones available from all the years available and are analyzed. The first tropical cyclones analyzed in each configuration of the model all possess similar statistics with respect to each configuration's joint distribution of vertically integrated temperature anomaly and low-level vorticity. The second tropical cyclones analyzed in each configuration of the model are all the strongest tropical cyclones in each configuration in terms of low-level vorticity value. It is found that for a given radiation scheme, tropical cyclones in configurations using the Kuo cumulus parameterization have the ability to become more intense than those forming in the configurations using the Arakawa-Schubert cumulus parameterization. It is also found that tropical cyclones in the configurations using the band model display a more realistic heating structure in the vertical. In terms of the frequency of storms predicted per year, the configuration of the FSUCGSM that pairs the Kuo cumulus scheme with the band model produces the most accurate results when analyzing the entire forecast period and shows skill against climatology-persistence forecasts. When the first 15 days of the model run are excluded, to account for model spin-up, the average of all four configurations becomes the most accurate and shows skill against climatology-persistence forecasts. It is also shown that the configurations using the band model simulate a more realistic subtropical high in the northern Atlantic, as well as a more realistic temperature profile in the vertical in the tropical Atlantic.