A new link between Indo-Pacific sea surface temperature variability and Australian region tropical cyclone counts

The annual number of tropical cyclones (TCs) in the Australian region has a well-known statistical relationship with the El Niņo-Southern Oscillation (ENSO), but the role of Indian Ocean sea surface temperatures (SST) remains relatively unexplored. Here we investigate a new link between SST variability in the sub-tropical to tropical South Indian Ocean (STSIO) and Australian seasonal TC counts, for the period 1969-2013. A suite of linear and nonlinear regression models reveal a strong and highly statistically significant relationship between SST anomalies in the STSIO and Australian region TC counts for a range of lead times. Composites of large-scale atmospheric variables tied to TC genesis potential suggest that the Indian Ocean subtropical ridge may be playing an integral part in the statistical relationship between the STSIO region and Australian TC counts. Work is ongoing to untie the confounding effects of ENSO, which phases with the STSIO for sub-periods of the full time series examined, as well as other physical mechanisms at play.