Condensation is a change in the combination of a substance from gaseous to liquid or solid. But what is condensation in the mastaba of the planet?

At each point in time, the Earth’s atmospheric planet contains over 13 billion tons of moisture. This figure is almost constant, since losses due to precipitation are ultimately continuously compensated by evaporation.

The moisture circulation rate in the atmosphere

The rate of moisture circulation in the atmosphere is estimated at a colossal figure - about 16 million tons per second or 505 billion tons per year. If all the water vapor in the atmosphere had condensed and precipitated, then this water could cover the entire surface of the globe with a layer of about 2.5 centimeters, in other words, the atmosphere contains an amount of moisture equivalent to only 2.5 centimeters of rain.

How long is a vapor molecule in the atmosphere?

Since on Earth an average of 92 centimeters falls out per year, therefore, moisture in the atmosphere is updated 36 times, that is, 36 times the atmosphere is saturated with moisture and freed from it. This means that the water vapor molecule stays in the atmosphere for an average of 10 days.

Water molecule path

Once evaporated, the water vapor molecule drifts usually hundreds and thousands of kilometers, until it condenses and falls to the Earth with precipitation. Water falling in the form of rain, snow or hail on the heights of Western Europe, covers about 3,000 km from the North Atlantic. Between the conversion of liquid water into steam and the precipitation on Earth, several physical processes take place.

From the warm surface of the Atlantic, water molecules fall into the warm moist air, which subsequently rises above the colder (denser) and drier air surrounding it.

If strong turbulent mixing of the air masses is observed, then a layer of mixing and clouds will appear in the atmosphere at the boundary of the two air masses. About 5% of their volume is moisture. Air saturated with steam is always lighter, firstly, because it is heated and comes from a warm surface, and secondly, because 1 cubic meter of clean steam is about 2/5 lighter than 1 cubic meter of clean dry air at the same temperature and pressure. It follows that humid air is lighter than dry, and warm and humid even more so. As we will see later, this is a very important fact for weather change processes.

Air mass movement

Air can rise for two reasons: either because it becomes easier as a result of heating and humidification, or because it is acted upon by forces that make it rise above certain obstacles, for example, over masses of colder and denser air or over hills and mountains.

Cooling

Rising air, once in layers with lower atmospheric pressure, is forced to expand and still cool. Expansion requires the expenditure of kinetic energy, which is taken from the thermal and potential energy of atmospheric air, and this process inevitably leads to a decrease in temperature. The cooling rate of the rising portion of air often changes if this portion is mixed with the surrounding air.

Dry adiabatic gradient

Dry air, in which there is no condensation or evaporation, as well as mixing, which does not receive energy in another form, is cooled or heated to a constant value (by 1 ° C every 100 meters) as it rises or falls. This value is called the dry adiabatic gradient. But if the rising air mass is moist and condensation occurs in it, then the latent heat of condensation is released and the temperature of the air saturated with steam drops much more slowly.

Wet adiabatic gradient

This magnitude of the temperature change is called the wet adiabatic gradient. It is not constant, but changes with a change in the amount of latent heat released, in other words, it depends on the amount of condensed steam. The amount of steam depends on how much the air temperature drops. In the lower atmosphere, where the air is warm and the humidity is high, the wet adiabatic gradient is slightly more than half the dry adiabatic gradient. But the wet adiabatic gradient gradually grows with height and at a very high altitude in the troposphere is almost equal to the dry adiabatic gradient.

The buoyancy of moving air is determined by the ratio between its temperature and the temperature of the surrounding air. As a rule, in a real atmosphere, the air temperature drops unevenly with height (this change is called simply a gradient).

If the mass of air is warmer and therefore less dense than the surrounding air (and moisture content is constant), then it rises up like a child’s ball immersed in a tank. And vice versa, when the moving air is colder than the surrounding, its density is higher and it drops.If the air has the same temperature as the neighboring masses, then their density is equal and the mass remains stationary or moves only together with the surrounding air.

Thus, two processes are present in the atmosphere, one of which contributes to the development of vertical air movement, and the other slows it down.