Water in the atmosphere

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

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

T°C

Density

0°

4°

Water

Other kindred substances

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

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

Evaporation goes on

Saturation has been reached

Condensation takes place

water phase transfer from state 1 to state 2 are

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

Recal ling that ,

0

water transfers from state 1 to state 2
Clausius – Clapeyron

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

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:

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

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

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.

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