Trade wind cumulus cloud

Trade wind cumulus (or trade cumulus) clouds are formed by cooling and moisture absorption of the dry trade winds over the relatively cold sea surface in the eastern parts of the oceans. These are clouds, typically Cumulus humilis or Cumulus mediocris, which are considered as fair weather clouds.

Characteristic for trade wind clouds is the uniform height of the upper cloud limit, which typically lies between 1000 and 1500 meters and thus indicates the altitude of the trade wind inversion. Due to orographic lift at mountains, the clouds can also rise higher, but the trade wind inversion also limits a further rise here, so that even in this case a light drizzle can occur at best. At night, the trade wind clouds usually dissipate again, especially over land.

Details of the development

The trade wind inversion is strongest in the eastern areas of the tropical oceans. Here, the sinking air masses of the Hadley or Walker circulation and the sea breeze ensure that the subsidence inversion lies particularly deep. Below this, a thin, very uniform layer of stratocumulus clouds forms in the marine atmospheric boundary layer. In these areas, the water surface temperatures are relatively low due to the upwelling of cooler, deeper water. As a result of the low-lying inversion and cool water temperature, moisture content increases within the marine boundary layer and, with saturation, clouds form over a wide area of the eastern tropical oceans.