2:30 PM - 2:45 PM
[ACG52-16] Analysis on the long-term trend of water vapor transport in winter over the northeastern Siberia
Keywords:Global warming, Changes in water cycle
It is well known that annual mean precipitation over the high-latitude land areas of the Northern Hemisphere has been significantly increasing due to the global warming since the middle of the 20th century. On the other hand, in the northeastern Siberia (NE Siberia) which is located at the easternmost part of the Eurasian continent, precipitation has been significantly decreasing particularly in the winter season. Our previous study showed that the observed decreases in precipitation over the NE Siberia may be caused by increases in the water vapor divergence, mainly due to weakening of the water vapor inflow from the North Pacific to the NE Siberia. In this study, we investigated the reason why the wintertime water vapor inflow from the North Pacific has been significantly weakening.
We analyzed the Japanese 55-year Reanalysis dataset for the 65-winter season from 1958 to 2023. We first decomposed the long-term changes in the water vapor flux into the terms of seasonal-mean product and the intra-seasonal variations. Then, we separated the seasonal-mean product term into the two terms; one is the term due to changes in horizontal wind and another is the term due to changes in specific humidity.
The term of the seasonal-mean product showed that southward changes of water vapor transport was dominant over western part of the Bering Sea, and the opposite trends appeared over the Alaska Peninsula. The term of the intra-seasonal variations also showed that poleward transport was weaken over the NE Siberia. The former term, which was showed more significant trends, was mainly influenced by the changes of horizontal wind. Comparing the horizontal wind vector and the height field between the first 10 years (1958 to 1968) and recent 10 years (2013to 2023) of the analysis period, we found that center of the Aleutian Low (AL) grew up and moved eastward for the latter period. Accordingly, the northward water vapor inflow to NE Siberia at the eastern side of the AL became weaken because of an eastward expansion of the AL.
We analyzed the Japanese 55-year Reanalysis dataset for the 65-winter season from 1958 to 2023. We first decomposed the long-term changes in the water vapor flux into the terms of seasonal-mean product and the intra-seasonal variations. Then, we separated the seasonal-mean product term into the two terms; one is the term due to changes in horizontal wind and another is the term due to changes in specific humidity.
The term of the seasonal-mean product showed that southward changes of water vapor transport was dominant over western part of the Bering Sea, and the opposite trends appeared over the Alaska Peninsula. The term of the intra-seasonal variations also showed that poleward transport was weaken over the NE Siberia. The former term, which was showed more significant trends, was mainly influenced by the changes of horizontal wind. Comparing the horizontal wind vector and the height field between the first 10 years (1958 to 1968) and recent 10 years (2013to 2023) of the analysis period, we found that center of the Aleutian Low (AL) grew up and moved eastward for the latter period. Accordingly, the northward water vapor inflow to NE Siberia at the eastern side of the AL became weaken because of an eastward expansion of the AL.