Nearly A Hundred Years, The Middle And Lower Reaches Of The Yangtze River Rainy Climate Variability Causes Research

The Meiyu over the Mid-lower reaches of the Changjiang River is a important part of summer rainfall in China. Abundance or deficiency of the Meiyu directly has effect on the disaster and its continuance of wet and drought in Changjiang and Huaihe region. So it is valuable to study the climatic abnormality cause of the Meiyu and provide the reference for short-term Meiyu climate forecasting.The relationship between interdecadal or interannual variation of the Meiyu series of the Mid-lower reaches of the Changjiang River and interdecadal or interannual variation of the global SST, SLP (sea level pressure) of the North hemisphere and sea ice concentration dataset are analyzed by using statistical diagnosing method.The results show that the El nino or La nina type is the typical distribution of the global sea surface temperature. The Meiyu in the Mid-lower reaches of the Changjiang River has a remarkably interannual and interdecadal climate variation. The interdecadal variations of the Meiyu and SST are related closely and the northwest Pacific is the region with the best relation. When the SST is colder than average in the north Pacific of the west wind drift ,or it is warmer in mid-east Pacific, drift area of west wind in the south Pacific and the middle part of the India Ocean, it will stand a good chance that it is rainy in Mid-lower reaches of the Changjiang River. That is to say when the SST has taken on Elnino(La nina) type , the Meiyu in the Mid-lower reaches of the Changjiang River is in the trend of the excessiveness(deficiency) with great probability. The influence of the SST interdecadal variation on the Meiyu represents the persistence. The prophase interannual abnormality of the west wind drift area in north Pacific, black current, warm pool and India Ocean are the main signals of the Meiyu abnormality.The distribution is the phase reverse between the high-latitude and the low-latitude district, which is the most distinctly structure characteristic of the sea level pressure in the north hemisphere. That is to say the distribution with centered polar region and circled along the zonal belt is the essential structure of the north hemisphere SLP interdecadal variation. Their relationship on the interdecadal variation is very clear between the Meiyu and the SLP. Such a correlation reflects that the large-scale variation of the SLP's circle structure would provide a background action for the interdecadal variation trend of the Meiyu. During the time at which this structure is strong ,accordingly the rainfall of the Meiyu is at the period of the more very likely; when the structure is weak, the precipitation of the Meiyu maybe is little. The previous winter and spring distributions structure of SLP are contrary between the north Atlantic, Mediterranean sea, the mainland of our country and the Iceland, the north Europe, which are the hard signals of the Meiyu rainfall abnormality.The trend of decreasing is very obvious of the interdecadal variation about sea ice area in different region and there is significant interannual variation in different region in every season. After separated in time scale, we can know clearly that the correlation between the interdecadal vairaition of the Meiyu and the interdecadal vairaition of different region sea ice area is very good. While the sea ice area of the different region is in the smaller stage, in all probability the rainfall of the Meiyu is in the abundant stage. The area variations in the Greenland sea of the spring and in the Kaka sea , Barents sea of the winter are the main signals of the Meiyu precipitation in the Mid-lower reaches of the Changjiang River.The synthesize action of the above factors are analyzed by the rotated principal component analysis. The results show that the Arctic sea ice played the important role to bring the abnormality of the Meiyu. In addition the previous anomaly change of the SST and SLP will have obvious effect on the Meiyu.