The Wave Train Characteristics of Teleconnection Caused by the Thermal Anomaly of the Underlying Surface of the Tibetan Plateau. Part Ⅰ: Data Analysis

The effect of the thermal anomaly of the underlying surface of the Tibetan Plateau in the previous winter and spring on the precipitation over the middle and lower reaches of the Yangtze River (MRYR) in the subsequent summer was investigated. Through data analysis, the influence of" strong signal" features of the three-dimensional thermal anomaly of the Plateau upon the precipitation anomaly over MRYR in the subsequent summer was revealed. This feature of the signal shows that from 0 cm to 320 cm under the surface of the ground, the soil temperature anomalies of the Tibetan Plateau manifest out of phase distribution in flood years and drought years over MRYR. In flood years over MRYR, there is a positive soil temperature anomaly in the region of the southern Tibetan Plateau (to the south of 30°N) and a negative anomaly in the region of the middle and northern Tibetan Plateau (to the north of 30°N), while in drought years the distribution of the soil temperature anomaly is opposite to the one in flood years. The maximum value of the soil temperature anomaly lies in the levels between 40 cm and 160 cm under the surface of the ground. Meanwhile, the data analysis also shows that the general circulation in the Northern Hemisphere may respond to the thermal anomaly of the Tibetan Plateau and form the propagation of a low frequency wave train with a seasonal time scale, and this wave train may affect the precipitation over MRYR in the subsequent summer.Analyses reveal that the thermal anomaly of the underlying surface of the Tibetan Plateau in the previous winter and spring is one of the key influencing factors for the subsequent summer precipitation over MRYR.