Water in the atmosphere

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.

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

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.

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

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)

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

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.

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

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.

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

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.