不同沙面地被物增温效应的初步研究

我国西北、华北大面积沙漠裸露 ,每到春季沙漠地区迅速增温 ,形成了以沙漠为中心的高温低压区 ,与西伯利亚每年春季向四周扩散的高压冷气流形成明显的气压梯度 ,这是我国西北、华北地区每年春季沙尘暴频繁的直接原因。( 1 )干燥的沙面对大气增温的作用最明显 ,其次是粘土 (干泥土 )。沙面对大气增温的方式有两种 :一是反射相对最强 ,在反射过程中对大气增温的作用明显。二是以热辐射、热对流的方式使大气增温 ,这是夏季和春、秋季干燥沙面使大气增温的最主要方式。( 2 )在同一地区约同一时间相同的日照下 ,沙面温度明显高于粘土、麦草沙障表面和沙生植物叶面温度。沙面在近地表 2 0 0 cm高度范围内气温成明显的递减趋势 ,而植物在近 5 0 cm上空范围内气温成递增趋势 ;在一定温度范围内 (夏季和春、秋气温较高时 )植物具有明显降低沙漠地区气温的作用。 ( 3 )在降低沙漠地区温度 ,减少沙尘暴方面植物固沙具有麦草沙障和粘土沙障等机械固沙措施不能替代的作用

A Preliminary Research on Increasing Temperature Effectiveness in Different types of Desert Ground covers

A large area of desert in northwest and north of China is bare and harsh. The temperature of the areas is increased rapidly in spring and it forms high temperature and low air pressure in some areas where deserts are the centers. In the meanwhile,the air pressure gradient is formed with high air pressure and cold air flow froms west of Siberia,and spreads widely and rapidly. This is the direct reason of sandstorm happening frequently in spring in northwest and north China. (1)The function of dry sand ground is the most remarkable for the air temperature increasing, second is the clay ground(dry clay). The research showed that there are two types of air temperature increasing: one is stronger reflection in sand ground areas, where the air temperature increasing is obvious in the reflecting processing. The other is thermal radiation and thermal convection,which is the main way for air temperature increasing when sand ground is dry in spring,summer and autumn. (2)The sand ground temperature is higher obviously than clay straw barrier ground and the leaf surface of natural desert plants under the same conditions of sunlight,time and the area. The air temperature within the height of 200cm from the sand ground is reduced gradually with the height increasing,The air temperature within the height of 50cm from the plant crown is increased gradually with the height increasing. The vegetation can reduce the air temperature obviously within a certain air temperature scale (when air temperature is higher in spring, summer and autumn).(3)The function of plant in sand ground can't be replaced by straw barrier and clay barrier and other mechanical methods for reducing air temperature and decreasing sandstorm in the desert areas.