Is the light black on the meteorological cloud picture a rain cloud system?

Visible light is a very narrow band, from 0.35 to 0.80 μ m. The satellite measures the solar radiation reflected from the surface of the ground cloud in the visible spectrum, and converts the radiation received by the satellite into an image, which is called a visible cloud image. The wavelength intervals of satellites in the visible spectrum are: 0.52 ~ 0.75 micron and 0.58 ~ 0.68 micron. The radiation received by satellites in the visible band is related to the albedo of objects and the zenith angle of the sun. If the zenith angle of the sun is smaller, the albedo of the object is greater, and the radiation received by the satellite is greater, and vice versa. On the visible light cloud map, the greater the radiation, the whiter the color tone; The smaller the radiation, the darker the color tone. Generally, the thicker the cloud, the greater the albedo and the whiter the hue.

Various cloud characteristics

(1) structural type: refers to the distribution pattern of image points with different light and dark degrees. For example, high-level cumulus clouds are often banded and vortex, and open cellular cloud systems are composed of cumulus clouds.

(2) Range size: refers to the distribution scale of cloud systems, from which the physical process of cloud formation can be inferred. Small-scale cloud systems are often related to small and medium-scale weather systems; Large-scale is related to large-scale weather systems.

(3) Boundary shape: Different types of clouds have different boundaries. For example, the boundary of cumulus clouds is irregular, and the boundary of stratus clouds (fog) is neat.

(4) Tone: refers to the brightness of an object image. The hue of the cloud on the visible cloud image is related to the thickness and composition of the cloud, while on the infrared cloud image it is related to the cloud top temperature.

(5) Shadow: refers to high clouds projected on low targets at a certain angle of solar altitude.

(6) Texture: used to indicate the roughness of the cloud top surface, such as the surface of stratus (fog) cloud top is even and smooth; However, the surface of cumulus clouds is uneven.

Characteristics of various clouds on satellite cloud images

A cirrus cloud: On the visible light cloud image, cirrus cloud has low albedo and is gray-dark gray; If cirrus clouds in visible light cloud images are white, their clouds are thick or overlap with other clouds; On the infrared cloud picture, cloud top temperature is very low and white. Whether it is visible light or infrared cloud image, cirrus cloud has fiber structure.

Cloud system classification map

B. Mesosphere clouds (upper clouds and cumulus clouds): On the satellite image, mesosphere clouds are connected with the weather system, showing a wide range of bands, swirls and commas. On the visible light cloud map, the middle cloud is gray-white to white, and the thickness of the cloud is determined by the different tones; On the infrared cloud image, the middle cloud is moderately gray.

C. Cumulonimbus clouds: The color of cumulonimbus clouds is the whitest in both visible light and infrared cloud images; When the high-altitude wind is small, the cumulonimbus cloud is round, and when the high-altitude wind is strong, there is often a cirrus anvil at the top, which is oval.

D. Cumulus Cumulus: The color of cumulus is very white on the visible light cloud image, but on the infrared cloud image, due to the different height of cumulus, the color of cumulus varies from gray to white, and the texture is uneven and the boundary is irregular. Its patterns are cumulus lines and perforated clouds.

E-stratocumulus (fog): On the visible light cloud map, stratocumulus (fog) appears as a smooth and uniform cloud area; The color tone is white to gray, and the color tone is very white if the thickness of stratus cloud exceeds 300 meters; Stratocumulus (fog) boundary is neat and clear, consistent with the trend of mountains, rivers and coastlines. On the infrared cloud image, the stratocumulus is darker in tone and in phase with the ground tone.