Satellite image of the Mania River in Madagascar
© NASA Earth Observatory image by Joshua Stevens, using Landsat data from the US Geological Surve
Uncommon clouds are gathering
A satellite view of the Mania River in Madagascar allows us to see a curious cloud pattern. It's common for cool, moist marine 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, but not over water. 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 the water 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 learning about an unusual weather pattern puts you on cloud nine, then join the United Nations in celebrating World Meteorological Day today. The UN created the annual observance 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.