16:30 〜 16:45
[ACC26-10] 第64次南極観測において観測された大気の川の気候学的特徴
キーワード：大気の川、南極氷床質量収支、第64次南極観測隊
An atmospheric river is a narrow, elongated corridor of strong vertically integrated water vapor transport (IVT) ahead of a cold front, playing a crucial role in meridional moisture transport between middle and high latitudes. The main moisture transport within the atmospheric rivers is concentrated in the lower troposphere due to the low-level jet stream, while the moist-laden air extends to the middle troposphere. Atmospheric rivers are well known as the phenomenon causing extreme precipitations and floods in the middle latitudes. Recent studies suggested that the atmospheric rivers would contribute to the Antarctic ice mass balance through snow accumulation and/or snow melt. However, their vertical structures and spatial distribution, essential to better understanding the spatial variability of the Antarctic ice mass balance, have yet to be well known. Therefore, this study investigated the atmospheric rivers observed by radiosondes during the 64th Japanese Antarctic Research Expedition (JARE64) cruise between December 2022 and March 2023 for their vertical structures and climatological characteristics.
During the JARE64 cruise, Research Vessel Shirase approached and observed five atmospheric rivers. All atmospheric rivers were located east of the low-pressure system and ahead of the cold front, consistent with the characteristics of atmospheric rivers in middle latitudes. From radiosonde observation, their vertical structures showed humid air extending to the middle troposphere, which was also similar to atmospheric rivers in the middle latitudes. Particularly, the atmospheric river observed on February 22 had a maximum water vapor and strong water vapor flux in the middle of the troposphere, showing different characteristics from those in previous studies in the polar region. In this case, the water vapor above 700hPa accounted for more than 60% of the total precipitable water. The analysis using the atmospheric reanalysis dataset revealed that this atmospheric river effectively would result in inland snowfall at the Antarctic ice sheet, although the other observed atmospheric rivers would contribute to the snowfall along the Antarctic coastal region.
A 40-year climatological analysis during Austral summer found that the observed atmospheric river on February 22 corresponds to the upper 5% of atmospheric rivers in an area-averaged IVT for 40 years. Such strong IVT atmospheric rivers are defined as extreme atmospheric rivers. The extreme atmospheric rivers show a distinctive spatial distribution, frequently appearing on the eastern Antarctic coast. The total precipitation when extreme atmospheric rivers make landfall in Antarctica accounts for 60% of the total summer precipitation in parts of East Antarctica.
During the JARE64 cruise, Research Vessel Shirase approached and observed five atmospheric rivers. All atmospheric rivers were located east of the low-pressure system and ahead of the cold front, consistent with the characteristics of atmospheric rivers in middle latitudes. From radiosonde observation, their vertical structures showed humid air extending to the middle troposphere, which was also similar to atmospheric rivers in the middle latitudes. Particularly, the atmospheric river observed on February 22 had a maximum water vapor and strong water vapor flux in the middle of the troposphere, showing different characteristics from those in previous studies in the polar region. In this case, the water vapor above 700hPa accounted for more than 60% of the total precipitable water. The analysis using the atmospheric reanalysis dataset revealed that this atmospheric river effectively would result in inland snowfall at the Antarctic ice sheet, although the other observed atmospheric rivers would contribute to the snowfall along the Antarctic coastal region.
A 40-year climatological analysis during Austral summer found that the observed atmospheric river on February 22 corresponds to the upper 5% of atmospheric rivers in an area-averaged IVT for 40 years. Such strong IVT atmospheric rivers are defined as extreme atmospheric rivers. The extreme atmospheric rivers show a distinctive spatial distribution, frequently appearing on the eastern Antarctic coast. The total precipitation when extreme atmospheric rivers make landfall in Antarctica accounts for 60% of the total summer precipitation in parts of East Antarctica.