Nimbostratus
Nimbostratus , Ns ( Latin nimbus "rain cloud" and stratus or sternere "expand, spread out, cover with a layer") is a more or less contourless, blue-gray cloud cover that usually begins at medium heights and often causes long-lasting precipitation .
Structure and appearance
Nimbostratus consists of (sometimes supercooled) water droplets and raindrops, ice or snow crystals or a mixture of the aforementioned liquid and solid particles. They arise through sliding movement on a warm front .
This type of cloud usually occurs as an extensive, low-lying, dark gray layer with a highly diffuse underside, from which persistent precipitation falls in the form of rain, snow, grains of ice or barrels of frost that does not necessarily reach the ground. In the tropics, especially during short pauses in the rain, one can observe how Nimbostratus breaks up into several different cloud layers that quickly grow back together.
The underside of Nimbostratus is often partially or completely covered by deeper lying, tattered clouds ( pannus ), which form on or below the Nimbostratus ceiling and change their shape quickly. Initially, these pannus clouds consist of isolated individual clouds; later they can merge into a coherent layer. If the pannus clouds cover large parts of the sky, special care should be taken not to confuse them with the underside of a nimbostratus cloud. Nimbostratus has neither special species nor subspecies. For special forms, accompanying and mother clouds, see article Cloud .
The horizontal extension of the Nimbostratus often reaches several hundred kilometers in width, corresponding to the course of the warm front. Due to the sliding movement of the warm front, the Nimbostratus is also very large in the direction of migration, which leads to hours of permanent precipitation ("land rain"), which often extends over the whole day. The Nimbostratus also belongs to the extended cloud genera vertically: Its upper limit is in the moderate latitudes at heights of 5 to 10 kilometers, which means that hardly any sunlight can penetrate the earth. As a result, the Nimbostratus has the status of the "classic bad weather cloud".
Differentiation from other types of clouds
In contrast to the Altostratus, the Nimbostratus has a darker gray color and completely covers the sun. Almost no precipitation falls from the Altostratus and only drizzle from the Stratus . The underside of the nimbostratus is indistinct and may show darker contours.
