Using correlation analyses, composite analyses, and singular value decomposition, the relationship between the atmospheric cold source over the eastern Tibetan Plateau and atmospheric/ocean circulation is discussed. In winter, the anomaly of the strong (weak) atmospheric cold source over the eastern plateau causes low-level anomalous north (south) winds to appear in eastern China and low-level anomaly zonal west (east) winds to prevail in the equatorial Pacific from spring to autumn. This contributes to the anomalous warm (cold) sea surface temperature the following autumn and winter. In addition, the anomalous variation of sea surface temperature over the equatorial middle and eastern Pacific in winter can influence the snow depth and intensity of the cold source over the plateau in the following winter due to variation of the summer west Pacific subtropical high.
Here we use harmonic analyses to examine seasonal variations of China land rainfall, low-level winds, and atmospheric heating over East Asia during spring to summer and the associated subtropical summer monsoon activities. Our results indicate that the South China spring rainfall (SCSR) in March is the prophase of East Asian sub-tropical summer monsoon (EASSM), and the onset of EASSM and China summer rainy season starts in early April, characterized by the enhanced rainfall in South China and the seasonal reverse of zonal land-sea thermal contrast in sub-tropical East Asia. The EASSM onset is earlier than that of South China Sea summer monsoon, and it is active in east of 100?E and north of 20?N. Our analyses suggest that the subsequent heating appears over India-China Peninsula in March and South China in April and causes the low-level atmospheric warming and the zonal land-sea thermal contrast seasonal reverse in East Asian subtropics. The atmospheric heating over South China is the main force to drive the southwesterly winds, updrafts and strengthen the summer precipitation in South China.
A new winter Aleutian Low (AL) intensity index was defined in this paper.A centurial-long time series of this index was constructed using the sea level pressure (SLP) data of nearly 100 years.The features of interannual and decadal variability of the winter AL intensity since 1900 were analyzed by applying the wavelet analysis.The relationship between the winter AL intensity and atmospheric circulation was examined.The cross-wavelet analysis technique was used to further reveal the relationship between the AL intensity and sea surface temperature (SST) in the equatorial eastern Pacific (EEP) and tropical Indian Ocean (TIO) in winter.The results indicate that:1) On the interannual timescale,the winter AL intensity displays 3-7-yr oscillations,while on the decadal timescale,8-10-yr and 16-22-yr oscillations are more obvious.2) Of the linkage to atmospheric circulation,both AO (Arctic Oscillation) and PNA (Pacific North America pattern) are closely associated with winter AL intensity on the interannual timescale,but only PNA contributes to the variation of winter AL intensity on the decadal timescale.3) As to the ocean impact,winter EEP SST is a major factor affecting the winter AL intensity on the interannual timescale,especially on the 3-7-yr periods.However,on the decadal timescale,though both the TIO and EEP SSTs are associated with the AL intensity in winter,the TIO SST impact is more significant.
On the basis of NCEP/NCAR version I daily reanalysis data from 1971 to 2000 and by the methods of inverse calculation,correlation analysis and comparative analysis,the influences of atmospheric heat source(AHS) over the Tibetan Plateau on the large-scale AHS and the general circulation in summer are studied in this paper.The results show that AHS over the plateau in summer may trigger a heat source wavetrain propagating northeastward along the coast from the East Asian continent and West Pacific to Bering Strait-Arctic or even North America.In addition,if AHS over the eastern plateau is intense,South Asian High moves to southeast and West Pacific subtropical high moves to southwest;on the contrary,if AHS over the eastern plateau is weak,South Asian High moves to northwest and West Pacific subtropical high moves to northeast.Therefore,South Asian High and West Pacific sub-tropical high move in the horizontally-opposite directions in terms of interannual variation,for which AHS over the eastern plateau seems to be thermodynamically responsible.
WANG YueNanZHANG BoCHEN LongXunHE JinHaiLI WeiCHEN Hua
There has been a lot of discussion about the atmospheric heat source over the Tibetan Plateau(TP)and the low-frequency oscillation of atmospheric circulation.However,the research on low-frequency oscillation of heat source over TP and its impact on atmospheric circulation are not fully carried out.By using the vertically integrated apparent heat source which is calculated by the derivation method,main oscillation periods and propagation features of the summer apparent heat source over the eastern TP(Q1ETP)are diagnosed and analyzed from 1981 to 2000.The results are as follows:(1)Summer Q1ETP has two significant oscillation periods:one is 10-20d(BWO,Quasi-Biweekly Oscillation)and the other is 30-60d(LFO,Low-frequency Oscillation).(2)A significant correlation is found between Q1ETP and rainfall over the eastern TP in 1985 and 1992,showing that the low-frequency oscillation of heat source is likely to be stimulated by oscillation of latent heat.(3)The oscillation of heat source on the plateau mainly generates locally but sometimes originates from elsewhere.The BWO of Q1ETP mainly exhibits stationary wave,sometimes moves out(mainly eastward),and has a close relationship with the BWO from the Bay of Bengal.Showing the same characteristics as BWO,the LFO mainly shows local oscillation,occasionally propagates(mainly westward),and connects with the LFO from East China.In summary,more attention should be paid to the study on BWO of Q1ETP.
