Impact of SST on Precipitation and Snowfall on the Sea of Japan Side in the Winter Monsoon Season: Timescale Dependency

We investigated the impact of the sea surface temperature (SST) over the Sea of Japan on precipitation and snowfall on the Sea of Japan side of Honshu, Japan, using precipitation and snowfall data from Automated Meteorological Data Acquisition System (AMeDAS) stations, records of sea level pressure from meteorological stations, wind fields from the Japanese 25-year reanalysis (JRA25) dataset, and multiple SST datasets. We examined the data on various timescales from daily to monthly because SST over the Sea of Japan also varies on timescales shorter than a month. The results showed that the impact of SST over the Sea of Japan on precipitation on the Sea of Japan side was strongly timescale-dependent. On the shorter intraseasonal timescales of several days to a few weeks, SST had a clear impact on precipitation, while the impact was indistinct when the 15-day and monthly averaged precipitation and SST values were used. On the other hand, cold surges over the Sea of Japan primarily accounted for the amount of precipitation on the Sea of Japan side. The timing and strength of cold surges controlled precipitation on all timescales. We clearly found the impact of cold surges on SST on 15-day mean values, compared with the pentad mean values. To understand detailed impacts of SST on precipitation, including air-sea interaction processes over the Sea of Japan, synoptic and shorter intraseasonal timescales should be examined in addition to seasonal or interannual timescales.