A Comparison of Northwest Cloudbands and Landfalling Atmospheric Rivers Over Australia

Abstract

Atmospheric rivers (ARs) are synoptic scale conveyors of tropospheric moisture. They have received considerable scientific attention in recent years due to their profound importance to the Earth's climate system and association with hydrometeorological extremes. The Australian Northwest Cloudband (NWCB) is a similar synoptic scale transporter of tropical heat and moisture which plays a large role in the country's complex hydroclimate. However, there are few studies which explicitly link the two phenomena and provide details on the nature of their relationship. Here we present a comparison of landfalling ARs with NWCBs in the Australian region using modified AR identification criteria for the summers and winters of 1998–2019. An autodetection algorithm was developed to identify AR shapes based on regionally sensitive vertically integrated water vapour transport (IVT) thresholds and common AR criteria. These shapes were then classified into AR events and assessed against recently developed NWCB criteria. Results suggested that while NWCBs likely represent a weaker subset of ARs, they account for a larger proportion of winter AR events than summer events. Significant seasonal patterns were observed in landfall location and IVT anomalies (via seasonal composites), suggesting different formation mechanisms for summer versus winter ARs and NWCBs.