High clouds with a height of more than 6000 meters are formed in the colder part of the troposphere. It belongs to three genera, all cirrus. At this height, water will solidify and crystallize, so this group of clouds is all made up of ice crystals. High clouds are generally fibrous, thin and mostly transparent.

● Cirrus clouds

It has a silky structure and silky luster, separating scattered clouds. Clouds are usually white and shadowless, and appear in the form of silk strips, feathers, ponytails, hooks, clusters, sheets and anvil. Cirrus clouds are less likely to see halos, and even if they appear, they are incomplete. In the northern and western plateau areas of China, there are sporadic cirrus snowfalls in winter. Before sunrise and after sunset, cirrus clouds are often bright yellow or orange under the reflection of solar light. In the cold season in the northern and western plateau areas of China, we sometimes encounter a low-altitude cloud, which looks like stratocumulus, but it has the characteristics of filamentous structure and silky luster, and sometimes it is dizzy, which should be recorded as cirrus clouds. If there is no cirrus feature, it should be recorded as stratocumulus. Cirrus clouds are divided into four categories:

(1) cirrus cloud (Ci fil): a thin and scattered cloud in the shape of silk strips, feathers and ponytails. Sometimes, even if it is polymerized into a long filament with a certain width, the whole filament structure and silky luster are still very obvious.

(2) Ci dens: thick and irregular cirrus clouds, sometimes with shadows in the middle, but the cirrus features at the edges are still obvious.

(3) Ci unc: It looks like a comma symbol, and there are small clusters or hooks at one end of the cloud.

④ Pseudo cumulonimbus (Ci not): It is formed by the separation of the top of bristle cumulonimbus from the mother. Clouds are big and dense, sometimes like anvil.

● cirrocumulus (Cc, cirrocumulus)

A cloud sheet or cloud layer composed of small-scale or spherical clouds, usually arranged in rows or groups, much like small ripples caused by a breeze blowing over the water. White without shadow, silky luster. Cirrocumulus can be evolved from cirrus and cirrostratus. Sometimes cumulus clouds can evolve into cirrocumulus. At the edge of the whole layer of cumulus clouds, sometimes there are small cumulus clouds, which are quite similar in shape to cirrocumulus, but don't mistake them for cirrocumulus. Only those who meet one or more of the following conditions can be considered as cirrocumulus.

(1) and cirrus or cirrostratus has obvious connection.

② It evolved from cirrus or cirrostratus.

③ It does have the silky and silky characteristics of cirrus clouds.

● cirrostratus (Cs, cirrostratus)

White transparent cloud curtain, when the sun and the moon pass through the cloud curtain, the outline is clear, the ground objects have shadows, and there are often halo rings. Sometimes the organization of the cloud is so thin that it is almost invisible that it only makes the sky milky white; Sometimes the structure of silk thread is indistinguishable, like a tangled thread. In the northern and western plateau areas of China, there can be a little snowfall in cirrostratus in winter.

Thick cirrostratus is easily mixed with thin high-level clouds. If the sun and the moon are distinct, the ground objects are shaded or dizzy, or the silk thread structure is cirrostratus; If we can only tell the position of the sun and the moon, the objects on the ground are shadowless, dizzy and high-level clouds. Cirrostratus can be divided into two categories:

(1) Thin-curtain cirrostratus: A uniform cloud curtain, sometimes so thin that it is almost invisible, and its existence is only proved by halo; When the cloud curtain is thick, you can't see any obvious structure, but the outlines of the sun and the moon are still clearly visible, and there are halos and shadows on the ground.

② cirrostratus: cirrostratus with obvious white silk structure and uneven cloud thickness.

Second, the Zhongyun clan.

Clouds form between 2500 meters and 6000 meters above sea level. They are made up of small water droplets that are excessively frozen.

● Cumulus clouds.

Hypercumulus clouds are small and well-defined, usually oblate, tiled, fish-scale or wavy dense clouds. Arranged in groups, rows and waves. The apparent width angle of most clouds is 1-5. Sometimes it appears at two or more heights. Thin clouds are white and thick clouds are dark gray. On the thin cumulus clouds, there are often rainbow colors around the sun and the moon, or Chinese rings with red outside and blue inside. Altocumulus can evolve with stratocumulus, stratocumulus and cirrocumulus. Cumulus clouds can be divided into six categories:

① Translucent cumulus clouds: The color of clouds varies from white to dark gray, and the thickness varies greatly. Even in the same cloud, there may be some differences between different parts. There are obvious individuals in the cloud, which are generally arranged quite regularly, but the transparency of each part is different. You can see the blue sky in the clouds. Even without clouds, the thin parts of clouds are brighter.

(2) shadow altocumulus (Ac op): A continuous layer of altocumulus, at least most of which are seamless, dark and irregular. Because the clouds are thick, dense and almost completely opaque, individuals at the bottom of the clouds can still be distinguished.

(3) Acclent: Acclent is scattered in the sky, oval or pod-shaped, with clear outline and constantly changing clouds.

(4) Cumulonimbus Altocumulus (Ac cug): This kind of cumulonimbus is formed by the extension of cumulonimbus and dense cumulus. In the initial stage, it is similar to shadow cumulus.

⑤ Ac flo: Clusters similar to small cumulus clouds, bottomless, with individual pieces like cotton wool, mostly white.

⑥ Ac cast: Cumulus-like clouds that develop vertically are juxtaposed in a line from a distance, with the same horizontal bottom and a prominent top, like a castle. Clouds are smaller than stratocumulus castles.

● As (high-level cloud)

Clouds with striped or fibrous structures are sometimes uniform, gray or gray in color, and sometimes slightly blue. In the thin part of the clouds, you can see the vague outline of the sun and the moon, which looks like a layer of ground glass. Thick high-level clouds, darker at the bottom, can't see the sun and the moon. Due to the different thickness of the cloud, the brightness of each part is different, but there is no obvious fluctuation at the bottom of the cloud. High-level clouds can drop continuous or intermittent rain and snow. If several rain (snow) banners hang down, the stripe structure at the bottom of the cloud can still be distinguished. High-level clouds are usually formed by cirrostratus thickening or nimbostratus thinning. Sometimes it can also evolve from shaded cumulus clouds. In southern China, sometimes cumulonimbus clouds extend in the upper or middle part, and can also form high-level clouds, but the duration is not long. High-level clouds can be divided into two categories:

① Translucent stratus (As tra): a thin and uniform gray cloud. Through the clouds, the outlines of the sun and the moon are blurred, as if separated by a layer of ground glass, and there is no shadow on the ground.

② Shadow high-level clouds (such as op): Clouds are very thick, and the thickness varies greatly. The thick part can't see the sun and moon through the clouds; The thin part is brighter and the fiber structure can be seen. It's gray and sometimes blue.

Third, the low cloud family.

Low clouds are formed in the atmosphere below 2500m, including thick and gloomy stratocumulus, stratocumulus (discontinuous stratocumulus) and thick and gloomy and rainy nimbostratus. Stratospheric grounding is called fog.