Satellite image of the Mania River in Madagascar

© Nasa Earth Observatory image by Joshua Stevens, using Landsat data from the US Geological Surve

Curious clouds. An unusual gathering of clouds

A satellite view of the Mania River in Madagascar allows us to see an unusual cloud pattern. It's common for cool, moist air to rise and form dense clouds over bodies of water, then for the clouds to evaporate as they drift over warmer, drier land. The opposite is happening here: Puffs of clouds are forming over land instead. That's because Madagascar's tropical rainforests are warm and wet enough that evaporating moisture rises as the day heats up. When it rises high enough, the moisture encounters cooler air, which condenses it into clouds. Generally speaking, clouds will form where the air is rising, which in this case is only over the land. Above the river, the air is cooler and descending, so no clouds are forming there.

If unusual weather patterns are your thing, then you might want to join the United Nations in celebrating World Meteorological Day today. The UN created the annual event back in 1950 as a day to recognise the contributions of meteorologists to our safety and well-being. We may not all know our cirrus from our cumulus, but we can at least thank meteorologists for letting us know if we should pack an umbrella or sunscreen.