This study proposes a new explanation for the formation of precipitation anomaly patterns in the boreal summer during the E1 Nifio-Southem Oscillation （ENSO） developing and decaying phases. During the boreal sum- mer June-July-August （JJA） （0） of the E1 Nino （La Nina） developing phase, the upper level （300-100 hPa） positive potential temperature anomalies resemble a Ma- tsuno-Gill-type response to central Pacific heating （cool- ing）, and the lower level （1000-850 hPa） potential tem- perature anomalies are consistent with local SST anoma- lies. During the boreal summer JJA（1） of the E1 Nifio （La Nifia） decaying phase, the upper level potential tempera- ture warms over the entire tropical zone and resembles a Matsuno-Gill-type response to Indian Ocean heating （cooling）, and the lower level potential temperature anomalies follow local SST anomalies. The vertical heterogeneity of potential temperature anomalies influences the atmospheric stability, which in turn influences the precipitation anomaly pattern. The results of numerical experiments confirm our observations.
Using the latest daily observational rainfall datasets for the period 1961–2008, the present study investigates the interannual variability of June–September （JJAS） mean rainfall in northern China. The regional characteristics of JJAS mean rainfall are revealed by a rotated empirical orthogonal function （REOF） analysis. The analysis identifies three regions of large interannual variability of JJAS rainfall： North China （NC）, Northeast China （NEC）, and the Taklimakan Desert in Northwest China （TDNWC）. Summer rainfall over NC is shown to have displayed a remarkable dry period from the late 1990s; while over NEC, decadal-scale variation with a significant decreasing trend in the last two decades is found, and over TDNWC, evidence of large interannual variability is revealed. Results also show that the interannual variability of JJAS rainfall in northern China is closely associated with the Northern Hemisphere circumglobal teleconnection （CGT）. Correlation coefficients between the CGT index and regional-averaged JJAS mean rainfall over NC and NEC were calculated, revealing values of up to 0.50 and 0.53, respectively, both of which exceeded the 99% confidence level.
The tropical Indian Ocean （TIO） is warmer than normal during the summer when or after the El Nio decays. The present study investigates the impact of TIO SST on the South Asian High （SAH） in summer. When the TIO is warmer, the SAH strengthens and its center shifts southward. It is found that the variations in the SAH cannot be accounted for by the precipitation anomaly. A possible mechanism is proposed to explain the connection between the TIO and SAH： warmer SST in the TIO changes the equivalent potential temperature （EPT） in the atmospheric boundary layer （ABL）, alters the temperature profile of the moist atmosphere, warms the troposphere, which produces significant positive height anomaly over South Asia and modifies the SAH. An atmospheric general circulation model, ECHAM5, which has a reasonable prediction skill in the TIO and South Asia, was selected to test the effects of TIO SST on the SAH. The experiment with idealized heating over the TIO reproduced the response of the SAH to TIO warming. The results suggest that the TIO-induced EPT change in the ABL can account for the variations in the SAH.
