Table of Content

    15 July 1963, Volume 29 Issue 3 Previous Issue    Next Issue
    1963, 29 (3):  175-187.  doi: 10.11821/xb196303001
    Abstract ( )   PDF (3262KB) ( )   Save
    Based on the field observations in various localities, some microclimatic features of undulating terrain are analysed. The main results are as follows: 1) It is just as pointed out by A. Woeikof that convex areas have a moderate climate while convex areas have an extreme one. The daily fluctuation of air tempera-tune and humidity is largest at the bottom of the valley smaller on the slop and smallesten the top of hill.2) The distribution of maximum and minimum temperature along the valley slope is shown as Fig.4, curve 1 represents temperature during clear weather with wind-speeds (v) at a height of 1.5 m above the ground less than 4 m per sec.;2-during clear weather, v-3.5 m/s; 3-during clear weather, v>5 m/s; 4-during cloudy weather, v<1m/s; 5-during over-cast weather, v=1.5 m/s. 3) In middle latitudes, the daytime temperature on a hill is highest on the south slope, lowest on the north slope. (Fig. l) 4) On a hill the isotherms in nighttime are generally parallel to the contours of the ground. The temperature becomes lower and lower as approaching to the foot of the hill (Fig. 2). 5) Fig. 7 shows the distribution of wind speed around a peak. The maximum of speed occurs at the top while minimum at the foot behind the peak. There are two secondary maxima near the middle of both slopes parallel to the wind direction and a secondary minimum at the foot of the windward slope. 6) In an undulating country the distribution of precipitation recerved by the rain-gauge is just contrary to that of wind. Wherever the wind is stronger, the precipitation is lesser, and vice versa. (Fig. 8) 7) Precipitation actually received by ground surface of a peak is largest in the lower part of its windward and beward slope and smallest at its top. Near the middle of the both sides parallel to wind, are also localities with much smaller precipitation.
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    1963, 29 (3):  197-206.  doi: 10.11821/xb196303003
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    In this paper after analyzing the diurnal variation of weather in Nan Shan region the auther pointed out the following phenomena. 1. In the high mountain region (absolute height over 4000 m) the air temperature falls down very slowly during the night time. Some times the mean diurnal variation of temperature shows semi-diurnal wave. 2. The mountain-valley winds predominant on the whole region of Nan Shan. 3. The mountain-valley winds are found to be disturbed by upper temperature trough. 4. The direction of reversed diurnally and annually.
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    1963, 29 (3):  207-218.  doi: 10.11821/xb196303004
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    As a main tributary of the Yellow River, the Wei Ho flows eastward in a graben, Central Shensi. The river course below Sian takes NEE direction in accordance with the Tsingling structural line. The present paper deals primarily with the channel types, the characteristics of the channel shifting, and the processes of erosion and deposition of the Lower Wei Ho. The Lower Wei Ho displays free meandering pattern. There are more than 30 al-ternating bends below Wei-Nan, while anastomosing is prevalent through certain cross-ings in the neighbourhood of the junctions of the Wei Ho and its tributaries. The formation of the meandering channel of the Lower Wei Ho depends chiefly on the following physiographic conditions: (1) the hydraulic gradient of the Lower Wei Ho is rather gentle (0.1‰-0.2‰);(2) the sediments of the Lower Wei Ho alluvial plain are mainly sub-loess (medium or fine silt, or clay admixed with moderate amounts of silt);(3) the Yellow River during its rising stage exerts a backwater effect on the Lower Wei Ho; and (4) as the Yellow River north of Tung-Kwan shifted its course east-ward during the past three decades, the Wei Ho has extended its mouth more than 10 kilometers forward and its gradient has become gentler than before. Figure 3 (in the main text), showing the tendency of the channel shifting of the Lower Wei Ho during 1915-1962, exhibits some important aspects: first, most of the bends shift downstream vigorously due to the action of sweeping; secondly, the transverse shifting to the left bank is rather pronounced than to the right; and thirdly, the chute cut-offs were easily formed at the rising stage during the past years. After analyzing the geomorphic processes of the Lower Wei Ho, it can be concluded that the meandering tendency is still going on, and the channel filling will develop to a certain extent in the near future.
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    1963, 29 (3):  241-249.  doi: 10.11821/xb196303006
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    The Minchin Oasis is one of the typical desert oases of China. Its area has ex-perienced some expansion in spite of the decrease of the river discharge and the shrink-age of the lake surface. The evolution of the drainage system of the oasis can be divided into three periods (the period of natural drainage, the period of semi-natural drainage, and the period of artificial drainage) and six stages (the Chung-Tuan bake stage, the Chu-ye Marsh stage, the Tu-ye Marsh stage, the Pai-Ting Lake stage, the Tsing-Tu Lake stage, and the Leap-forward Irrigation Channel stage). Throughout all these periods and stages the volume of water of the rivers and lakes was on the decrease, and the natural drainage system was finally replaced by the artificial drainage system-reser-voirs and irrigation channels. The decrease of the river discharge was not caused by the desication of the climate but by the destruction of natural vegetation cover and the diversion of the water for irrigation in the upper courses of the rivers. After the libera-tion, the project of land reclaimation and water conservation in large scale carried on in the arid regions of the Northwest has opened a new era for the Minchin Oasis.
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