美国山地降水量垂直分布的研究

根据美国西部山地资料,依据宏观地理因素和局地海拔高度因素从各种气候区域和不同纬度上选择典型坡地研究了降水的垂直分布规律。

RESEARCH ON VERTICAL DISTRIBUTION OF MOUNTAIN PRECIPITATION IN THE UNITED STATES

In the paper precipitation normal data from 1951 to 1980 in the Unitec States are used to make research on mountain precipitation distribution.According to geographical positicn and climatic situation, we selected eleven slopes.The western slope of the Cascades Mts., the western slopes (37N and 39N) of the Sierra Nevada Mts., the southwestern and eastern slopes of the Rocky Mts., thh southern, southwestern and eastern slopes of the Colorado Plateau as well as the western and southeastern slopes of the Appalaching Mts. The conclusions can he drawn as follows.1.The mountain precipitation in the United States does not always Increase with height simply.Their distribution have four patterns. (1) Precipitation increases with height without or with the maximum precipitation height or with the second maximum precipitation height probably. (2) precipitation decreases with height at first, then it increases with height.2.The first maximum precipitation height exists mainly on the windward slopes where elevation above see level is height of more than 1500 meter and its height increases with aridity of climate.3.On the slope higher than 2500m A.S.L. of the western slope (37N)in the Sierra Nevada Mts. the increase of precipitation with height again is observed. It is a result that airflow climbs up the slope twice experiencing ascending-descending-ascending process.4.The increasing (lapse) rates of precipitation with height are not uniform and related to geographical position, exposure of the slope and season. Generally the increase of precipitation with height is the fastest at the lower slope on the windward slopes of westerly airflow, and increments or decrements are much larger in rainy season than in dry season, and seasonal differences of the rate values at each height are larger. On the leeward of the westerly airflow the precipitation almost does not change and even decreases with height at the lower slope and the largest increment of precipitation with height often appears at the upper slope or nearby peak and seasonal differences of the rate values at each height are smaller.5.There are experiment relation between annual precipitation (P_z) and elevation above sea level(Z)on all the selected slopes of the mountains in the United States as follows:P_z=a(b-z)z+c, where a, b and c are determinant cofficients and they change with region.6.Annual maximum precipitation height on the windwaid slopes almost dose not change from year to year, but its annual precipitation has large interannual variation.However, there is a good linear regression correlation between annual precipitation of footfill and maximum precipitation height. The correlation coefficient is very high and regression effect is quite remarkable.