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Clouds over inland waters

Amazon Estuary | Northeast Brazil

Dates of acquisition:
September 15th, 2023  |  13:52:55 UTC
September 7th, 2023  |  09:31:02 UTC

Sensor: Sentinel-2B L2A

Coordinates:     ca. 1°S, 51.5°W

Areas along the equator are among the cloudiest land areas on earth. During calm weather it can be less cloudy over rivers and lakes than over the adjacent land areas.
In the early morning hours, the sun begins to warm the surface and the warm, humid air rises and cools as it rises, forming low clouds.
Since water has a relatively high heat capacity, it takes longer to warm a water body (river or lake) than e.g. bare soil but also forests. The air above water is therefore cooler and the thermic effects are weaker. If the water body is large enough, less moisture rises to the atmosphere over the river or lake and consequently less clouds are formed.
From a satellite it is clearly visible that  rivers and lakes are often cloudless when the wind does not transport clouds from the surrounding area, while the surrounding tropical rainforest (e.g. around the Amazon [Figure 1] or the Congo River [Figure 2]) is quite densely covered with small, low-moving, low-flying cumulus clouds.

Fig. 1
Fig. 2
Images contain modified Copernicus Sentinel Data [2023].