逆温层原理 Inversion layer principle
在对流层大气中，通常情况下温度随高度的升高是降低的。如果气温随高度的升高反而增高的话，这就称为 “逆温”，相应的大气层就叫“逆温层”。从热力学的角度看，无论是等温层还是逆温层都表示大气层是稳定的。如果它们形成在对流层中某一高度上，则会阻碍下方垂直运动的发展。由于这种原因，近地层空气中的水汽、烟尘以及各种有害气体，上天无路，入地无门，只有飘浮在逆温层下面的空气层中，使整个天气阴沉，压得人透不过气来，同时也便会闻到煤烟味和其它难闻的气味。In troposphere, the temperature decreases with altitude. However, if the temperature becomes increase with altitude, it is called “Inversion temperature” and the air layer is called “Inversion layer”. From the thermodynamics, “inversion layer” represents that the air layer is very stable and it will stop vertical movement of air if it is formed in a certain height closed to ground. So, in this case, the steam, smoke, dust and some harmful gas in the air have no way to go and float under the inversion layer. At this time, sky becomes very cloudy, it makes people be hard to breath, and people can smell strong malodor.
“逆温层”的形成有很多种，最常见的是 “辐射逆温”, 辐射逆温是夜间因地面、雪面或冰面、云层顶部等的强烈辐射冷却，使紧贴其上的气层如地表层的空气就降到了上层空间某一高度的温度，这样地表层与 “与其等温”的上层空间之间就形成了一个“逆温层”。 如下图所示 There are many kinds of “inversion layer”. The most common inversion layer is called “Radiation inversion layer” that used to be formed during night time when the ground become cold and the cold radiation makes the ground surface air cool down to a degree that is same with the temperature in a certain height, so the “inversion layer” is formed between ground surface air layer and the certain height air layer.
近地层的辐射逆温，一般是在日落前后由地面开始形成，夜间随着辐射冷却的加强，逆温层逐渐加厚，黎明前达到最大厚度。日出后从地面开始逐步消失。它的垂直厚度可以从几十米到400来米，Inversion layer closed to ground used to be formed in evenfall, the dimension of the layer becomes thick during the night time due to the lower temperature, and it reaches the biggest thickness before sunrise. It starts to disappear after the temperature increase in daytime. The thickness of the inversion layer could be dozens meters to around 400 meters.
冬春时节大陆上高压控制的天气条件下，由于长时间的辐射冷却的结果，地面和近地层空气的温度显著下降，可形成在白天也不消失的冬季辐射逆温。这种逆温层的厚度可达几百米到3千来米。In winter and spring, a “winter radiation inversion layer” used to be formed because of the constantly lower temperature on the ground. The thickness of this kind inversion layer can reach hundred meters to three thousand meters.
在低洼地区（谷地、盆地）因辐射冷却，冷空气沿斜坡下沉流入低洼地区形成逆温。这叫“地形逆温”, 比如，在垃圾场的外围的低洼地区就很容易形成地形逆温。In lower area such as valley and basin, the cold air flows and sinks into the lower places to form the inversion layer that is called “Terrain Inversion Layer”. For example, it is easy to form terrain inversion layer in the lower places or valley around the landfills.