Annual Analyses of Basin and Hemispheric Tropical Cyclones Indices

Tropical cyclone activity has received widespread attention in 2005 with the occurrence of the most active Atlantic Basin hurricane season on record and new studies of tropical cyclone frequency and intensity. While recent conclusions have pointed to increasing trends in tropical cyclone intensity, additional analyses are necessary for fully understanding global and basin trends as well as inherent problems and assumptions that must be taken into consideration. This paper will present analyses of the annual intensities, numbers and other related indices of tropical cyclones over basin and hemispheric spatial scales. Typically, annual tropical cyclone statistics are presented as numbers of storms, but other indices provide different perspectives on the magnitude of a particular year with respect to the historical record. The reliable data that resides in the historical archives are limited primarily to the satellite era, especially in the under-reported basins such as the Indian Ocean, Australia and the South Pacific. In particular, reliable sustained wind data are required for integrated statistics, such as the Accumulated Cyclone Energy (ACE) Index, in order to accurately calculate the index. The analyses presented will focus on basic statistics and integrated indices determined over each of the seven tropical cyclone basins globally, as well as indices determined over each hemisphere on an annual basis.