Arctic oscillation signals in the East Asian summer monsoon

The present study examines the relationship between the Arctic Oscillation (AO) and the East Asian summer monsoon. Two rainfall data sets are used. One is obtained from 10 stations along the Yangtze River to the southern Japan and the other from gridded global land rainfall data for the period 1900-1998. All data are high-pass filtered before analyzing to highlight the interannual variability. Results show that the AO significantly influences on year-to-year variations in the East Asian summer monsoon rainfall. When AO leads by one month, the correlation between May-July AO and summer total rainfall is -0.44. When AO leads by two months, correlation becomes -0.32. Of all monthly, May AO shows the strongest connection to the summer monsoon rainfall. Correlation coefficient between them is -0.45. The large-scale atmospheric circulation patterns in East Asia in association with the AO are also evident. A positive phase of the AO in late spring is found to lead to a northward shift in the summertime upper tropospheric jet stream over East Asia. This northward shift of the jet stream is closely related to anomalous sinking motion in 20degrees-40degreesN and rising motion in surrounding regions. These changes give rise to a drier condition over the region extending from the Yangtze River valley to the southern Japan and a wetter condition in the southern China. Possible mechanisms connecting the late spring AO and summer monsoon rainfall are suggested.