DIFFERENCES OF INTERDECADAL OSCILLATION BETWEEN MEAN TEMPERATURE OF NORTHERN AND SOUTHERN HEMISPHERE AND THEIR INFLUENCES ON WARMING SIGNAL

On the basis of multi-taper spectral analysis, the work not only has examined and reformed monthly mean temperature time series of the Northern Hemisphere (NH) and Southern Hemisphere (SH) from 1856 to 1998, but also has systematically contrasted the differences of interdecadal oscillation (IDO) between the hemispheres, ocean-land surface in different seasons, with special analysis of IDO signals effects on global warming. The results show that the warming trend plays a dominant role in hemispheric mean temperature variability during the last 150 years. However, there are significant IDO with periods of about 40, 60 - 70 years superimposed on a linear warming trend for NH mean temperature which leads to the reduction of the linear warming rate in terms of its significance and stability, as opposed to that in the SH, especially in summer. Moreover, in comparison of land to sea surface temperature, IDO signals detected in the latter are found to be more remarkable than those in the former, as contrasted to the linear warming rate. It has been noticed that IDO shows its peak value in the middle 1990s and begins to descend recently, a fact that probably affects the coming warming rate of NH mean temperature. Meanwhile, In terms of the GCM results from the HadCM2 model, preliminary analysis implies that the IDO may be the inherent oscillation of the ocean and atmosphere system, but warming trends are not related to natural variability.