Mountains move like clouds

Clouds as a weather sign

Clouds: Fibrous like hair or clumpy and clumpy

More than half of the earth's surface is constantly covered by clouds. Scientists estimate that around 15 trillion tons of water circulate in the atmosphere - 300 times the volume of Lake Constance.

Most people only know that clouds are made up of condensed water. Science, on the other hand, classifies the celestial structures into ten different genera, each of which has a few sub-forms.

Latin names describe their properties: Fibrous and like hair they can be, for example (cirrus), heap-like and lumpy (cumulus) or layered and low-hanging (stratus).

Ten types of clouds, three levels of altitude

Basically, clouds occur at three different altitudes: There are high (in our latitudes at a height of five to 13 kilometers, for example cirrus clouds), medium-high (at a height of two to seven kilometers, for example altocumulus clouds) and low clouds (below two kilometers, for example stratus clouds).

There are also types of clouds that extend over all altitudes. The most impressive are the huge, tower-like thunderstorm or cumulonimbus clouds: When they build up kilometers high in the sky - when viewed from below, they appear black because no more sunlight can get through - then even the meteorological layman suspects that a severe storm is imminent.

More experienced cloud viewers can also infer the appearance of a warm front with rain from condensing high cirrus clouds. The medium-high, undulating altocumulus clouds, on the other hand, herald rather stable weather. With the thick gray stratus clouds, which form a dense layer not that far from the ground, it can be seen that they usually have persistent rain in their luggage.

Mysterious cloud formation

Basically, clouds are formed when warm, moist air rises and cools down to the so-called dew point. This describes the temperature at which the previously invisible water vapor in the air condenses into liquid droplets.

There can be various reasons for the air to rise: With convection, the air absorbs the heat from the ground, becomes lighter and moves upwards. Even if it hits an obstacle, such as a mountain, warm air can escape upwards. In addition, a cold front can also move warm, moist air upwards by pushing itself under it like a wedge.

The condensation of water at great heights can only work if so-called condensation nuclei are present. These are particles that have to be of a certain size and are also called aerosols: Grains of dust and sand, bacteria, salt or sooty remains of human air pollution.

But when and how exactly clouds form, what exactly has to happen so that a cloud begins to arise from the moisture in the air, that is still a secret for scientists, which is currently being researched in different places.

The cloud in the tower

At the Leibniz Institute for Tropospheric Research in Leipzig there is a cloud simulator on which researchers can observe the birth of a cloud under laboratory conditions. A cloud several meters long and only millimeter thick is formed in a tower here, and it is barely a minute old.

It's a pretty nebulous proposition, but it is designed to help researchers answer important questions: Under what conditions do the droplets begin to form? How fast are they growing? Which particles have to be present in which density in order to make the cloud appear in the sky? Answering these questions could also provide further information about how we humans are changing the climate.

More rain on the weekend?

What is certain is that the clouds help determine climatic processes in various ways, because they can keep the sun's rays away from the earth and at the same time hold back the earth's heat. In addition, the water evaporating from the earth takes heat energy up with it and distributes it around the globe when clouds form.

And we influence the formation of clouds with our pollutant emissions by increasing the amount of condensation particles in the atmosphere. This can be seen, for example, in the condensation trails on airplanes, which in principle are nothing more than man-made clouds.

Scientists have been able to show why the weather is often worse on weekends than during the week. Because of the rush hour and work in industrial plants, a particularly large amount of aerosols are released into the air on weekdays. It takes a few days for them to accumulate, and then towards the end of the week they are most focused. This creates a lot of clouds and therefore it rains more often on weekends.