Diagnostic Studies On The Inter-annual And Inter-decadal Variability Characteristics Of The Arctic Oscillation

In this paper, the spatial-temporal structure of Arctic Oscillation is analyzed; the effect of the mid-high latitude atmospheric circulation anomaly to the summer rainfall of eastern China is discussed. During the analyses, a few of diagnostic methods such as harmonic wave analysis, SVD, complicated EOF (CEOF), composite analysis and correlation analysis are used. The main results are as the followings:1 ) The climatological and anomalous spatial-temporal characteristic ofthe atmospheric circulation in the extra-tropical region is analyzed. Polar vortex is a basic circulation system which exists in every season (strong in winter and weak in summer) and can extend to the lower level of stratosphere. The polar oscillations in north and south hemisphere (AO, AAO) give the spatial-temporal characteristic of the polar vortex anomaly. The polar oscillation is a teleconnection system which similar to that of North Atlantic Oscillation (NAO), North Pacific Oscillation (NPO)and Southern Oscillation (SO).2) Polar oscillation are obviously zonal symmetry and seasonal variation (strong in winter and weak in summer). Polar anomaly, showed by polar oscillation index, has obvious inter-annual and inter-decadal variation. The space patterns show that the inter-annual variation is related with polar circulation anomaly (AO) and the inter-decadal variation is related with sub-tropical circulation anomaly (sub-tropical oscillation, STO). The differences of the polar oscillation between north and south hemisphere are obviously reflected in that: (1) the annual variation of principal pattern of zonal symmetric circulation anomaly component is morn stronger in north hemisphere than in south hemisphere; (2) In 55°N, 500hPa level, the propagation characteristic of zonal asymmetric circulation anomaly component is standing wave in north hemisphere and eastward wave in south hemisphere.3) In this paper, the index of polar vortex position is introduced. This index can preferably describe the variability of mid-high latitude circulation anomaly. The anomalous variation of polar vortex in winter corresponds to the situation that the pattern of mid-high latitude circulation anomaly in troposphere is AO and STO.4) In the inter-annual and inter-decadal time scale, the summer SSTA between north Atlantic and north Pacific is significantly correlated. AO and STO also significantly correlated with SSTA index. This correlation can be illuminated by the 1000hPa wind field which is coupling with the SSTA pattern and the corresponding polar vortex anomaly.5) The analyses show that AO and STO are significantly correlated with the SST's principal teleconnection pattern between north Atlantic and north Pacific in inter-annual and inter-decadal time scales; circulation anomaly in pole and sub-tropical region is significantly related with SST's inter-annual and inter-decadal teleconnection respectively. So AO and STO is the "atmospheric bridge" which connects the north Atlantic SSTA with north Pacific SSTA.6) Under the inter-annual and inter-decadal scale, summer AO and STO have distinct contemporary and lag correlation with precipitation anomaly in eastern China. For the contemporary relationship, under the inter-annual scale the precipitation anomaly in the Changjiang valley is markedly related with STO (correlation coefficient is 0.425) and under the inter-decadal scale the precipitation anomaly in the Changjiang valley is strongly correlated with NA and STO(correlation coefficient is 0.668 and 0.749). Among those correlations, the contemporary correlations is related with eastern China summer monsoon anomaly resulted from the ocean-atmosphere coupling of north Atlantic and north Pacific, resulting in the evident relationship between the two oscillations and the summer precipitation in eastern China.