Low water clouds

Low water clouds
Satellite Instrument

Low level water clouds appear yellow in the HRV Cloud RGB images.

Water droplets strongly reflect short wave solar radiation, hence the strong intensity of the red and green colour beam (red + green = yellow) .

The blue colour contribution from the window channel IR10.8 has an average value caused by the relatively warm cloud tops. It contributes more when the cloud tops are colder. Especially in the winter season, when low stratus and fog are most frequent (see image below), they depict in yellow tones. The colder the cloud tops are, the more the yellow will turn into grey (and white for very high opaque clouds). Notice that the intensity of the blue colour beam intensifies with decreasing cloud top temperatures.

On the image below, the HRV Cloud RGB shows low stratus and/or fog in central Europe.


HRV Cloud RGB from 19 December 2015, 12:00 UTC

The image below shows ship trails over the Atlantic. Water in the exhaust from cargo vessels condensates and forms long trails. These low level water clouds can be seen in the HRV Cloud RGB.


Ship trails over the Atlantic ocean.

Explanation of the yellow colour of low-level clouds in the HRV Cloud RGB (see the recipe):

Only the HRV channel contributes notably to the HRV Cloud RGB for low level clouds. The addition of red and green results in a yellow tone.