Precipitation in the Lake Baikal basin associated with different patterns of atmospheric blocking over Western Siberia

摘要

Since 1996, a low-water period has been observed in the Lake Baikal basin. The decrease of inflow to Lake Baikal isrelated to reduce of the summer discharge of the Selenga River, whose basin makes 83.4% of Lake Baikal catchmentarea. The decrease of river discharge is mainly due to a decrease of midsummer precipitations over the basin that occurs,preferentially, when the frontal system of the East Asian summer monsoon weakens. Some authors suggested that thereason for the East Asian summer monsoon variations is the features of atmospheric circulation at the mid- and highlatitudes of Eurasia. In particular, atmospheric blockings can play an important role.We previously showed the features of formation of July rainfall in the Selenga River basin in different positions ofblocking over Eurasia. We showed that precipitation tends to fall out in Mongolian part of the river basin when blockingis displaced from Western Siberia (WS) to Eastern Siberia (ES). Blocking in these cases may have a dipole configurationwith anticyclonic part over Eastern Siberia and cyclonic part over Mongolia.In this work we continue to study blockings over Siberia and their relations with precipitation in the Selenga Riverbasin in July. As a result we have formulated the following summaries regarding the relationship of WS-blocking andprecipitation in the Selenga basin.1. The maximum amount of precipitation is possible in case of complete blocking offset from West to East Siberiaand formation of blocking over the eastern Siberia.2. The amount of precipitation is not high if the blocking moves from the WS to the ES without formation ofblocking over the eastern Siberia.3. Precipitation in the basin does not fall out in the case of the blocking, which weakly shifts at the end of their lifecycle.4. There is a relationship between lifetime, intensity blocking and its movement over the WS. The stronger theblocking over the WS, the less it moves.