< p >云需要水分,因此高云将存在于上层的地区水分。综观规模提升是cm / s的,这不是一个有效的方式把水分从表面上水平。< / p > < p >认为这水汽图像:< br > < img src = " https://i.stack.imgur.com/ibT5x.gif " alt =“水蒸气”> <子>来源:学院杜佩奇NEXLAB < /订阅> < / p > < p >在这幅图像中,颜色代表中期的湿度和对流层上层。鲜艳的颜色代表上级水分。深色的颜色代表水分在中期的水平。黑色代表干中部和上部的水平。< / p > < p >最亮的白人(水分)的最高水平是在ITCZ和相关中纬度气旋位于美国东北部。这些都是与对流有关的区域,这与天气尺度流动是一种有效的水分运输到对流层上层。这个对流外流将先与“砧”雷雨,但随着流水在上面的水平可以表现为卷云。ITCZ是由赤道辐合和哈德利的向上分支细胞。 Mid-latitude cyclones have a so-called "wet conveyor belt" that transports near-surface moisture into the mid and upper levels which can then manifest as upper level clouds (or lots of rain/snow). To answer "why are most cirrus clouds in the tropics?" I would associate that with the large transport of water vapor into the upper levels by the persistent convection in the ITCZ.