JMSJ Highlights

Editor's Highlight : Ishizaki et al. (2025)

Takahashi, K., and T. Sakazaki, 2025: The climatological features of atmospheric rivers and their role in water vapor transport in the south polar region. J. Meteor. Soc. Japan , 103 .
https://doi.org/10.2151/jmsj.2025-020
Early Online Release
Graphical Abstract

Editor in charge: Kei Yoshimura

Their proposed method reveals a zonally asymmetric, spiral-like AR frequency distribution extending from the mid-latitude Atlantic to the high-latitude Southern Pacific, with three distinct maxima in the Atlantic, Indian, and Pacific Oceans—features not reported in previous studies.
ARs account for 70% of total meridional moisture transport, shaping precipitation patterns over Antarctica. AR occurrence peaks from fall to winter, while individual AR intensity is strongest from summer to fall.
The study highlights long-term trends and their impact on ice sheets. While AR intensity shows a positive long-term trend in DJF and MAM, the detection number remains stable. ARs contribute to both increased snowfall and ice shelf calving, underscoring the need for further research to quantify their net impact on Antarctic ice mass balance.

Abstract
In recent years, Atmospheric Rivers (ARs) have been recognized to influence the Antarctic ice sheet via extreme snowfall, latent and sensible heat transports, and anomalous changes in radiation balance. ARs are defined as extreme moisture transport events and are thought to account for a significant fraction of total moisture transport from mid to high-latitude regions, such as Antarctica. While previous studies have investigated ARs associated with extreme events over Antarctica and the Southern Ocean, their climatological features remain poorly understood. We investigate the climatology of ARs in the south polar region such as their geographical distribution and their role in moisture transport, by using an AR detection method that extracts the area with a localized moisture transport at 6-hourly intervals for JRA55. Notably, our method effectively describes the geographical distribution of ARs, contrasting with conventional methods that use temporal fixed criteria. We find that the contours of climatological AR frequency display a zonally asymmetric, spiral-like structure extending from mid-latitudes in the Atlantic to high-latitudes in the Pacific Ocean. This distribution produces a zonal asymmetry in meridional moisture transport, which may contribute to the observed zonally asymmetric distribution of Antarctic precipitation. We also suggest that the dominant meteorological systems associated with the ARs differ geographically: extra-tropical cyclones in the Atlantic and blocking events in the Pacific Oceans. At 60°S, we find that the AR detection number has not had a significant trend over recent decades, but the typical intensity of individual ARs in austral summer has increased over the last 41 years.