近半个世纪以来,我国气象工作者对东亚夏季风和我国汛期降水量的关系进行了一系列的研究并取得了很多有意义的结果。但过去大多数作者多注意低层季风活动、气团属性和锋系对雨带变动的影响,而对经圈垂直环流和雨带的关系讨论较少。

In this paper, the variation of decade (10 days) rain-band during flood season in the eastern China is investigated. It has been found that the seasonal migration of rain-band is closely related to the movement of the wedge line of subtropical high at the 500 mb level, the displacement of subtropical jet and the variation of the vertical circulation along 115癊.According to the synoptic situation and climatic features, the vertical circulation asso-ciated with decade rain-band of 1978 and 1979 may be classified into five types:(1) The Spring rainfall type in the south of the Yangtze riverFig. 1 shows the distribution of decade rain-band and vertical circulation along 115癊 in this case. It is characterized by the existence of the direct circulation cell between 26癗 and 34癗. The rain-band connecting to the ascending branch of the cell lies between the Yangtze river and the Nanling mountains. The wedge line of subtropical high is located at about 14癗. The axis of 200 mb subtropical jet maintains at 30癗. In general, this type appears in April and May.(2) The rainfall type in south China in the early SummerAn example of this is shown in Fig. 2. The axis of rain-band in correspondence with the north ascending branch of monsoon circulation cell, which is near Kuangzhou, extends along the Nanling mountains and rainfall is quite heavy. At this time, the axis of subtro-pical jet is located at 36癗. This type appears from 2nd decade of May to 1st decade of June.(3) The plum raift type in the Yangtze and the Huaihe valleysAn example of this type is shown in Fig. 3. It is characterized by the existence of the strong monsoon circulation cell and the east:-west plum rain-band corresponding to the as-cending branch of the cell. It can be seen that the rain-band lies in the Yangtze valley, and the wedge line of subtropical high is located at about 22癗, but the axis of subtropical jet still maintains at 35?36癗. The northerly wind prevails in the upper part of the tropo-sphere. The Qinghai-Tibet high at 100 mb level belongs to "the west type".(4) The persistent drought type in the Yangtze and the Huaihe valleys in mid-Summer This type appears in July and August. Fig. 4 shows the distribution of rain-band andvertical circulation along 115癊 in 1st decade of July, 1978. It can be seen that the southern component of wind and the descending motion predominate in the whole troposphere. And in the vast subtropical regions of south to the 33癗 persistent drought occurs. The wedge line of subtropical high is located at about 26癗. The Qinghai-Tibet high belongs to "the east type".(5) The drought type in the Yangtze and the Huaihe valleys at the end of summer, meanwhile rain area shifts to the further north in North China.A selected case is shown in Fig. 5. It shows that the monsoon circulation cell is very strong and stable in North China. The rain-band corresponding to the ascending branch of the cell lies in North China, while in those vast regions of south to the 35癗 drought ap-pears because of strong descending motion, except the south-eastern coast of China, where some new rain areas occur. In addition, the wedge line of subtropical high is located at 34癗, and the axis of subtropical jet advanced to 45癗. The strong ascending motion just appears on the south side of the axis.Some results of this paper might have indicative significance for long-range forecast of rainfall tendency.