Effect of High-Resolution SST on 60km-AGCM Simulated Snowfall in Japan

Abstract

The effects of sea-surface temperature (SST) on snowfall in Japan were investigated using a high-resolution 60-km-mesh atmospheric general circulation model (AGCM). We used a high-resolution SST dataset (original resolution, ∼20 km); the high-resolution SST data resolve warm boundary currents, such as those of the Kuroshio and Tsushima warm currents. The AGCM experiment using high-resolution SST data simulates snowfall increase (decrease) over warm (cold) SST regions in January better than the AGCM based on coarse-resolution SST data. A moisture budget analysis shows significant rainfall increase over a warm-SST band along the boundary current, where large evaporative fluxes supply moisture to the atmosphere. On the other hand, the moisture convergence anomaly is generally opposite to that of the evaporative flux anomaly, and hence acts to reduce rainfall. The surface moisture flux change is generally similar to the dynamical term, while the thermodynamic term also plays a non-negligible role. A comparison of satellite observations and AGCM experimental results shows that fine-scale SST variations affect surface wind patterns. Furthermore, we diagnosed surface convergence anomaly using two terms: one that describes the vertical mixing effect and the other that describes the pressure adjustment effect. This analysis shows that both vertical mixing mechanisms and pressure adjustment may contribute to surface convergence anomaly over the Japan Sea.