Relationship between the Tibetan Snow in Spring and the East Asian Summer Monsoon in 2003: A Global and Regional Modeling Study

In 2003, a climate extreme accompanying a wet and cool summer over East Asia was recorded over the East Asian countries including central China, Korea, and Japan. A possible relation of this record-breaking summer in East Asia to above-normal snowfall over the Tibetan Plateau in spring has been investigated using the National Centers for Environmental Prediction (NCEP) global and regional models. The changes in the simulated East Asian summer monsoon circulations in response to snow anomalies over Tibet are highlighted. The results from both global and regional model experiments suggest that above-normal snowfall over the Tibetan Plateau in May induces a weakening of the Tibetan high, which leads to the formation of favorable upper-level circulations accompanying cyclonic circulation anomalies covering the East Asian region in summer. These circulation anomalies in response to the snow anomalies over the plateau are more robust and closer to what was observed in the regional than in the global model results. The sensitivity experiments also show that the precipitation and lower-level circulation anomalies in summer, caused by the snow anomalies in spring, influence the above-normal precipitation in the lower reaches of the Yangtze River basin, as revealed in previous observational studies. However, the experiments do not fully explain the observed signals in Korea and Japan since the spring snow anomaly over Tibet plays a role in weakening the western Pacific subtropical high in the simulated summer, whereas in reality the intensity of the high was stronger than normal in 2003.