| dc.description.abstract | This study investigates the interannual variation of synoptic scale disturbance, and its influence on the characteristic of precipitation. This study utilizes a composite method, which isolates the affect of ENSO, to
understand the evolving process of circulation field in Eastern Asia under theinfluences of ENSO.
In the ENSO warm phase, the Siberian ridge in upper troposphere weakens but the Siberian high in lower troposphere follows to weaken. There is a negative anomaly of surface pressure around the Siberian high area including China. The Alaskan ridge in upper troposphere also weakens but the Eastern Asian main trough in upper troposphere strengthens during the ENSO warm phase, so that the Aleutian low shifts to the east. There is a positive anomaly of pressure in lower troposphere over west Pacific Ocean. In lower troposphere, the negative anomaly of pressure in China and the positive anomaly of pressure in west Pacific Ocean bring warm-wet air into Eastern Asia. On the other hand, a positive anomaly of synoptic scale disturbances in the upper troposphere propagates to Eastern Asia along the monsoon route. At the same time, the ridge over 20oN in upper troposphere in west Pacific Ocean moves to the east. It is advantageous the synoptic scale disturbance to increase in lower troposphere in Eastern Asia. Because of more synoptic scale disturbances and warm-wet air, the precipitation will increase in Eastern Asia.
In the ENSO cold phase, because the Siberian ridge in upper troposphere strengthens, the Siberian high strengthens in lower troposphere. There is a positive anomaly of pressure in lower troposphere around the Siberian high area including China. In upper troposphere at the same time, the Eastern Asian main trough shifts to southwest, and the Alaskan ridge strengthens. Aleutian low in lower troposphere shifts to southwest, so there is a negative anomaly of pressure in lower troposphere in west Pacific Ocean. In lower troposphere, the positive anomaly of pressure in China and the negative anomaly of pressure in west Pacific Ocean bring cold-dry air into Eastern Asia. For disturbance field, the ridge over 20oN in west Pacific in upper troposphere extends to west and it is advantageous the synoptic scale disturbances to decrease in lower troposphere in Eastern Asia. Because of less synoptic scale disturbances and cold-dry air in lower troposphere, the precipitation will decrease in Eastern Asia. | en_US |