An Automated Climatology of Cool-Season Cutoff Lows over Southeastern Australia and Relationships with the Remote Climate Drivers

Cutoff low pressure systems have been found to be the synoptic system responsible for the majority of rainfall in southeastern Australia during the cool season (April-October inclusive). Meanwhile, rainfall in southeastern Australia at the seasonal and interannual scale is known to be related to remote climate drivers, such as El Niño-Southern Oscillation, the Indian Ocean dipole, and the southern annular mode. In this study, a new automated tracking scheme to identify synoptic scale cutoff lows is developed, and then applied to 500-hPa geopotential height data from the NCEP1 and ERA-Interim reanalyses, to create two databases of cool-season cutoff lows for southeastern Australia for the years 1979-2018 inclusive. Climatological characteristics of cutoff lows identified in both reanalyses are presented and compared, highlighting differences between the NCEP1 and ERA-Interim reanalyses over the Australian region. Finally, cool-season and monthly characteristics of cutoff low frequency, duration, and location are plotted against cool-season and monthly values of climate driver indices (oceanic Niño, dipole mode, and Antarctic Oscillation indices), to identify any evidence of linear correlation. Correlations between these aspects of cutoff low occurrence and the remote drivers were found to be statistically significant at the 95% level for only a single isolated month at a time, in contrast to results predicted by previous works. It is concluded that future studies of cutoff low variability over SEA should employ identification criteria that capture systems of only upper-level origin, and differentiate between cold-cored and cold-trough systems.