Trends in tropical cyclones in the South Indian Ocean and the South Pacific Ocean

Abstract

The statistical significance of trends in tropical cyclones (TCs) in the South Indian Ocean (SIO) and the South Pacific Ocean (SPO) has been examined. Calculation of significance is based on nonparametric Monte Carlo methods, and in addition we explore whether a constant model, a linear model, or a simple breakpoint model represents a best fit to the data. For the 1981–1982 to 2006–2007 TC seasons, there are no apparent trends in the total numbers of TCs (by which, in this study, we mean those tropical systems attaining a minimum central pressure of 995 hPa or lower), nor in numbers of 970 hPa TCs in the SIO and the SPO (such TCs being called severe in the Southern Hemisphere). Positive trends in the numbers of 945 hPa and 950 hPa TCs in the SIO are significant but appear to be influenced to some extent by changes in data quality. In the Australian region, no significant trends in the total numbers of TCs, or in the proportion of the most intense TCs, have been found.