Abstract
Antarctica plays a crucial role in modulating the global climate system, but it is equally important to consider how Earth’s climate moderates Antarctica. This study focuses on the latter, and in particular, atmospheric rivers (ARs). These are transient, filamentary regions that transport anomalously large amounts of moisture from the subtropics towards the high latitudes, and so are a crucial feature of moisture transport towards Antarctica. As filamentary structures, the occurrence and pathway to Antarctica is influenced by mid-latitude planetary wave development, extratropical cyclone dynamics, and tropical circulation variability. Previous studies have assessed the role of smaller groups of southern hemisphere climate variability modes in modulating ARs in Antarctica, but there has not yet been a comprehensive review of all these relationships within the context of tropical variability such as that associated with the Madden Julian Oscillation (MJO).
This study uses ERA5 data to focus on the delivery of moisture to 70°S as a ‘gateway’ to the Antarctic coastline, and splits the continent into three regions (East 1, East 2, and West) to account for different large-scale climatologies. Over the 1979-2024 period, East 1 has the lowest net moisture flux in comparison to the West and East 2 regions. There are statistically significant increases in AR frequency over East 1 during spring, and over West in the summer. Monthly correlations of meridional moisture flux and climate variability modes show that variability over the Pacific Ocean associated with the Pacific South American (PSA) pattern is the main driver of mid-latitude moisture delivery to the Antarctic coastline. Daily correlations to the MJO reflect a complex relationship with meridional moisture transport, but demonstrate that enhanced convection over the Maritime Continent and central Pacific Ocean can initiate an Indo-Pacific wavetrain that extends further eastward around Antarctica as a modification of the PSA pattern.
Significant moisture transport events for each region were identified, with the tropical-to-polar atmospheric setup analysed over the preceding twenty days. For all three events results suggested that interactions between El Niño Modoki and the MJO play an important role in Antarctic ARs. Furthermore, all three events were associated with Rossby wave breaking, which produced anticyclonic flow over each region. The East 1 event initiates from moisture supplied by Amazonia followed by lee cyclogenesis, whereas the East 2 event resulted from MJO convection over the Maritime Continent initiating an Indo-Pacific wavetrain. In contrast, the West event was related to Cyclone Pam, the strongest MJO values on record, and El Niño Modoki conditions Future work should investigate the MJO's combined role as a moisture source and Rossby wave source in generating downstream teleconnections based within a moist isentropic framework. By improving understanding of the mechanisms that enable extreme moisture transport to Antarctica, these findings contribute to more robust interpretations of Antarctic hydroclimate variability and its implications for future climate change.