Of course, there are no giant scales in the world on which we could place our object of study, so we will rely on calculations. Especially since they have already been done before us by Peggy LeMone, a researcher at the U.S. National Center for Atmospheric Research, who was also intrigued by this question.
A cloud gets its mass from the tiny droplets of water or ice crystals it contains. One such tiny droplet weighs almost nothing, but if you add them all together…
In different types of clouds (cirrus, cumulus, stratus) the concentration of such droplets varies. The water density in a cumulus cloud is about 0.5 g per cubic meter. We recall from school physics lessons that mass can be obtained by multiplying volume by density. Scientists decided to take as a basis the most typical-sized «white-maned little horse» about one kilometer wide and arrived at a volume of one billion cubic meters.
By doing some simple calculations, it becomes clear that the mass of an average cumulus cloud is 500,000,000 grams, or 500 tons. To picture it more vividly, let us compare it with the mass of the largest land animal – the elephant. Its weight is about 6 tons, so an average cloud weighs as much as 80 of these savanna dwellers.
But cumulonimbus clouds, the ones we call storm clouds, are even heavier. In them the density of water droplets reaches its limiting values. The weight of such menacing clouds, ready to pour down on the earth as rain, can reach 2,000 tons, and that is already more than three hundred elephants.
Why, then, does such a giant float across the sky rather than fall down? The thing is that the temperature inside a cloud is slightly higher than that of the surrounding air, owing to the heat released when water vapor turns into droplets. This is what allows them to stay aloft. And when the density of the droplets inside reaches its limit, the cloud sheds its «ballast» in the form of rain. But by no means do all the droplets reach the surface of the earth; some of them evaporate along the way and return to their cloud homes.
