Water in the atmosphere

of the weather. An important element of the weather is

cloudiness. There are many types of clouds. Some of them are beautiful, some gloom, some are terrible.
Of course, a fat lot they care what we think of them, but it is not so for us. The form, shape, and movement of clouds are indicators of the processes occurring in the atmosphere. It means that the clouds can serve as predictors of the weather. Therefore, the real meteorologists should be familiar with all aspects of the cloud “life”.
Precipitation, like cloudiness, are of different kind: rain, snow, drizzle, sleet etc. In turn, the rains can be divided into different forms: widespread, pouring, drizzling. There are some special form of rain. Every of them has its inherent name.

there is one particular one the people call “TSAREVNA’S TEARS”.

That is the rain which can not be named by any other name but this.

The drops of this rain look larger than usual raindrops, They seem to fall slower from a small cloud. The Sun shinning from a side and reflecting from the drops makes them as if they are made with gold. Being transparent, they bear blue color from that part of the sky which is not covered with clouds.

Gold and blue combination makes them so beautiful that the name “ tsarevna’s tears” seems to be the most appropriate name for this rain.

found in all three phases: vapor, liquid, and ice.
Special character

of the water density variation.



Water heat capacity significantly changes when congealing to the solid state. That is
not so for other kindred substances.
Water freezing and boiling temperature are much higher than that of other kindred chemical combinations.

T°C

Density

0°

4°

Water

Other kindred substances

a good solvent, it has chemical activity (iron rusts as

contacting water)
Liquid water density varies with temperature a little. It can be regarded as constant (1 g/cm³), as well as ice (0.91 g/cm³).
Water vapor heat capacity can be also regarded as non-depended on temperature variation.

molecules comes back,
Evaporation
Saturation state at
At
Condensation
If the temperature in the closed

space increases to become
evaporation will begin again until

Evaporation goes on

Saturation has been reached

Condensation takes place

water phase transfer from state 1 to state 2 are

possible

Water vapor

Liquid water

Ice

The first law of thermodynamics can be applied to describe the water phase transfer processes

Let’s introduce the notion of thermodynamic potential

denotes entropy (it is a term known from general physics)

temperature
Thermodynamic potential remains unchanged at the water phase transfer from

one state to another.
At temperature T+dT, Ф+dФ, and E+dE., and

Recal ling that ,

0

water transfers from state 1 to state 2
Clausius – Clapeyron

equation

For the process

For practical purposes the quantity is neglected because it is very small (T°C). Therefore, the latent heat is adopted as constant.

the same reasoning, we’ll obtain the similar formula for sublimation

process.

Magnus formula

Much better results were obtained with empirically determined coefficients “a” and “b”

air
C-Saturated air

01°C), E0=6,1114 hPa
At T>0,01 water can be in two phases:

liquid and vapor.
At T≤0,01 water can be found in any phase.

Due to adhesion forces the equilibrium water vapor pressure over super cooled water is larger than over ice.

are curvature of the evaporating surface, salt solution, and electric

charges.

Easier come off

Hard come off

In the atmosphere we deal with convex surfaces (droplets). To determine the saturation water vapor pressure over droplet of the radius r, meteorologists use Thomson's formula.

Is surface tension coefficient

For practical purposes

the surface tension coefficient depends upon temperature as indicated in

the table.

In fact, the parameter Cr is not constant, but its variation is so small that we may neglect them.
The ration Er/E can be calculated for different values of the droplet radius.

For the condensation to start over very small droplets ( ) the super saturation must be 300 – 400%. If the droplet radius is the saturation is about 100%. It means that curvature, at this case, doesn’t influence saturation, and, hence, condensation.

condensation nuclei (ядрах конденсации) that are particles of various salts.

Thus, the droplets actually are chemical solutions. The saturation over solution is always smaller than over pure water (at the same temperature).

m is the mass of the salt dissolved in the droplet, M is the solution mass ( mass of the droplet), is the solution density, is pure water density, Cm is coefficient depending on the nature of the salt.

Presence in droplets of electric charges (Q) should also be accounted for.

Is dielectric permissivety

Is electric constant