Seasonal evolutions of the summer Asian-Pacific teleconnection and associated atmospheric circulation and rainfall

Using the 1981-2007 daily atmospheric reanalysis data and rainfall data as well as statistical analysis methods, the summer (May to September) atmospheric teleconnection over the Asian-Pacific region is investigated， and the seasonal variation of this teleconnection and its links with the Asian Pacific atmospheric circulation and the Asian monsoon rainfall are analyzed. The results show an extratropical teleconnection between Asia and the North Pacific in the daily upper tropospheric temperature disturbance in May to September, similar to the Asian Pacific Oscillation (APO). On the seasonal scales, when the upper troposphere is warmer in the midlatitudes of the Asian continent, it is colder than normal in the midlatitudes of the North Pacific, and vice versa. This out of phase varying feature in the upper-tropospheric temperature between Asia and the Pacific also occurs in the middle and lower layers of the troposphere and the lower stratosphere. The APO index not only indicates the varying features of summer extratropical zonal thermal contrast between Asia and the Pacific but also better reflects the variability of the summer meridional thermal contrast between Asia and tropical Indian Ocean. The largest APO index often occurs in middle July to early August and tended to occur earlier from 1981 to 2007. When the summer APO index is high (low), the upper-tropospheric South Asian High in the Asian continent and the underlying low pressure system are strong (weak) and the subtropical North Pacific high is strong (weak) and shifts its location northwards (southwards). The upper-tropospheric tropical easterly wind jet and the lower-tropospheric southwesterly winds are strong (weak) over the Asia-Africa region. The precipitations increase (decrease) in a large region from India to southern China and in northern China as well as over northeastern Asia.