The Impact of Observational Technology on Climate Database Quality: Tropical Cyclones in the Tasman Sea

Abstract

The recorded climatology of tropical cyclones that affect the Tasman Sea spans the period from 1911 to the present. This climatology is a subset of the much larger Australian Tropical Cyclone database, which is the official record of all tropical cyclones in the Australian area of responsibility. Such a long, detailed record should provide an excellent dataset for regional climate research. However, a detailed analysis of the database has revealed that it must be used with caution over the Tasman Sea, where statistically significant discontinuities are present, greatly reducing its quality and length for climate and climate change studies. Problems with the complete Australian Tropical Cyclone database have been identified and discussed earlier by a number of authors. This study is concerned with two statistically significant discontinuities that occurred in the Tasman Sea portion of the database in the mid-1950s and in 1977. The first discontinuity almost trebled the recorded frequency of tropical cyclones, whereas the second discontinuity exhibited an opposite trend, decreasing the recorded frequency of tropical cyclones by a factor of 8 from the previous period. Some possible explanations for the abrupt changes in this subset of one particular database are discussed. It is suggested here that the most likely explanation is the improved observing technology and the associated changes in interpretation of the new data. Finally, it is likely that other climate databases have been affected by similar problems and should be treated with the same degree of caution.