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CHARACTERISTICS OF GROUND TEMPERATURE IN PERMAFROST AREAS IN THE NORTHERN PART OF GREAT XINAN MOUNTAIN

Dai Jingbo ( 3rd Survey and Design Institute, Ministry of Railway )  
The ground temperature variation in the permafrost layer in the northern part of the Great Xinan Mountain depends on the latitudinal location of a given region, i.e.from south to north and from southeast to northwest associated with the increasing of latitude and atmospheric temperature decreases. On the other hand, the continuity and the thickness of permafrost increase, so the temperature of permafrost gradually becomes lower. This tendency is especially obvious on the northwest slope of the Great Xinan Mountain. The depth of variation of mean annual ground temperature in permafrost areas in the northern part of the Great Xinan Mountain is generally 12-18 meters or so and 14-15 meters seemingly in majority. According to the variation of amplitude within the depth of the annual ground temperature variation, it may be divided into the zone of diurnal temperature variation, the zone of positive and negative temperature variation, and the zone of permafrost temperature variation. Based on the type of ground temperature curve in permafrost, it may be divided into the positive gradient ground temperature curve,the negative gradient ground temperature curve, the zero gradient ground temperature curve, and the twisty form ground temperature curve. Among them, the type of positive gradient ground temperature curve usually happens in the permafrost region in the northern part of the Great Xinan Mountain and the type of zero gradient ground temperature curve usually distributes near to the southern boundary of permafrost. Under the influence of the extensive: and sustained human's activies, the ground temperature of permafrost arises, and the type of negative gradient ground temperature curve is formed from the change of positive gradient ground temperature curves. The type of twisty form ground temperature curve occurs scarcely.
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