The formation of the rain belt and the structure of the Barn front at the lower troposphere on the Chinese continent during the rainy season (June and July) have been studied. As the first step, the daily precipitation distributions were classified in terms of the morphology of the precipitation area and the formative location of the rain belt. Next, the concurrent relationships between the changes of synoptic fields and the formation of the rain belt were investigated. Finally, the characteristic features of the frontal system for each type were analyzed to show the manifold structures of the Baiu front on the Chinese continent.
Data sets used in this paper are daily precipitation records from 234 rain gauge stations (Fig. 1-a) and atmospheric data at 12GMT from 85 stations (Fig. 1-b) during the years 1977 to 1981.
The daily precipitation areas having synoptic scale can be classified morphologically into two groups: a circular precipitation area (here in after, CPA) whose diameter is 1, 000km or more, and a belt-shaped precipitation area (here in after, BSPA), oriented in an almost east-west direction. The BSPA, which is mainly seen south of 35°N on the Chinese continent (Fig. 3-a), can be divided into two types in terms of the initial formation site (Fig. 3-c). Furthermore, the BSPA sometimes appears to west-southwest of the CPA. Accordingly, the transition patterns of the precipitation area resulting in the formation of the BSPA could be classified as follows:
Type A (7 cases): The BSPA is formed after the passage of the CPA (Fig. 4).
Type B-I (11 cases). The precipitation area which appeared on the Tibetan Plateau moved or extended eastward without forming a CPA, and the BSPA built up to the north of 30°N (Fig. 5 type B-I).
Type B-II (6 cases): Similar to type B-I, but the precipitation area moved or extended southeastward, and the BSPA built up to the south of 30°N (Fig. 5 type B-II).
Figure 6 indicates the appearance period of the BSPA for each type. Type A and type B-II took place in early to mid-June, and type B-I occurred frequently after mid-June. On the Chinese continent, the occurrence of The BSPA is chiefly due to type B-I, which lasts longer than other types but often is punctuated with intermissions.
The BSPA of type A corresponds to the convergence line due to the southerly and the northerly or westerly trend in the western part of the synoptic scale cyclone which coincides with the CPA (Fig. 7 type A-a). In this case, the meridional gradient of temperature around the BSPA is not recognized (Fig. 7 type A-b and Fig. 12 type A). The synoptic scale cyclone appears to develop according to the incursion of cold air from a higher latitude to the east of the Tibetan Plateau (Fig. 9).
The formation of the BSPA in the absence of a CPA (type B-I and type B-II) is closely related to the appearance of a cold air mass in the lower troposphere. The BSPA is formed where the humid air, in a state of convective instability from south of the BSPA, is lifted up by the cold air mass and releases its instability (Fig. 12 type B-I, type B-II ), Therefore, the BSPA of type B-I and type B-II is considered to correspond to the front with a comparatively large meridional temperature gradient.
The cold air mass in type B-I can be traced back to the eastern foot of the Tibetan Plateau (Fig. 10) and is accompanied by an anticyclone in the lower troposphere (Fig. 7 type B-I and Fig. 11 type B-I ). On the other hard, the cold air mass in type B-II is derived from the Yellow Sea or the Japan Sea as a cold northeasterly or easterly air current (Fig. 7 type B-Il and Fig. 11). This cold air current seems to be established by an anticyclone to the east of North China Plain (Fig. 8 type B-II). Furthermore, the equivalent potential temperature to the north of the BSPA is lower in type B-II than in type B-I (Fig. 14 type B-II ).

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Since world war II, rural areas and village communities in Japan have been changing very rapidly. As a result village communities have varied from traditional to urbanized ones in their functions. The author thought that village communities vary in their degree of assimilation to the socio-economic systems of the whole society, which have brought forth the differentiation of rural areas, and that there is some relationship between the functional change in village communities and the differentiation of rural areas. Therefore, in this article the author tried to clarify this relationship.
For this purpose the rural area around Hamamatsu City (in Shizuoka Prefecture) was selected as a study area (Fig. 1). Hamamatsu City, which has strongly influenced the rural area around it, is located in the so-called Tokaido Megalopolis. Thus the study area includes both extensive agricultural production areas resulting from high industrialization and intensive truck farming areas.
Two kinds of associations, agricultural and administrative, are recognizable in each village as organizers of the community. In traditional village communities the two associations combine and have all-round functions, but in urbanized village communities the agricultural association is specialized to perform only agricultural functions and the administrative association, administrative functions.
Therefore, in this article the investigation was conducted by the following procedure: first, differentiation in the study area was examined through a spatial structure of two dimensions, agricultural and residential, which were analyzed by the principal component analysis. Second, the village communities were classified according to their functions, which were indicated by the characteristics of the agendas for the associations' meetings. And functional change in the village communities was investigated through the classification. Finally, the relationship between functional change in the village community and the differentiation of the study area were investigated. The results of the study as follows:
1) The rural areas around Hamamatsu City are spatially differentiated into three concentric zones. In the inner zone, agricultural production is declining and immigrants from the urban areas are becoming the majority of the population. In the middle zone, agricultural production is briskest, and immigrants are not so numerous. In the peripheral zone, agricultual production is less brisk than in the middle zone, and immigrants are very few (Fig. 5).
2) The village community, whose characteristics are investigated in terms of relationship between two associations, has changed from a traditional combined type to a divided one, a specialized one or a weakened one. The divided or specialized type sometimes functions better than the combined type, but not the weakened type. These new types of village communities are spatially distributed near built-up areas or main traffic routes (Fig. 8).
3) The village communities differ from the traditional type in terms of tow factors, decline of agricultural production and immigration of newcomers. The former weakens the agricultural association and the latter alters the administrative association to the specialized type or the weakened type. In a village where agricultural production is brisk in spite of the development of urbanization, the farmers want to keep the agricultural association form being separated from the administrative one, to avoid a social and spatial division between farmers and non-farmers and the social problems that can be caused by immigration from urban area into a traditional community (these are called konju-ka problems). In a village where the agricultural production has declined and newcomers are a major portion of the population, the village community takes on the character of a suburban community.

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