A Reanalysis of Australian Region Tropical Cyclones in the Geostationary Satellite Era. Part 2: Wind Radii Parameters Using the Deviation Angle Variance Technique (DAV-T)

The Australian tropical cyclone database is the official resource for tropical cyclone information for all southern hemisphere tropical cyclones that existed between 90ºE and 160 ºE. In particular, it contains information on the location and intensity of any tropical cyclone since 1906 and, since 2007, information on wind field structure. However, because of the changes in observation platforms historically, wind structure information is often not available in the historical TC database. Yet, this information is vital to understand the variability and long-term trends in TC physical characteristics as well as the impacts they have on oceans and land. The “objective reanalysis of tropical cyclones in the Australian region of the geostationary meteorological satellite era” project takes advantage of techniques that have been recently developed to objectively analyse TC intensity and wind field parameters using geostationary satellite data as its primary input. The final product will be a completely objective, satellite-based TC analysis from 1981 to the present that is complementary to the official tropical cyclone database.

The reanalysis of TC intensity is described in Part 1 of this study. For the wind field parameter reanalysis, the deviation angle variance technique (DAV-T) for wind field specification (Dolling et al. 2016) is used to extract the radius of 34- 48- and 64-kt winds in all four quadrants of the TC. DAV-T measures the axisymmetry of cloud structures relative to a reference point in IR satellite images to determine the level of cloud organisation in tropical systems. The map of variances that is constructed using the DAV-T has a high correlation with the two-dimensional wind field. When combined with sea-surface temperature and some information on the age and maximum intensity of the TC in a regression model, the resulting wind field radii have been shown to have relatively low errors compared with other techniques. One challenge of performing this analysis in the Australian region is a lack of good verifying observations. In this presentation, we will discuss the data, methodology, challenges, and results.