Specifying the amount of water vapor in the atmosphere is important
for several reasons:
- Water is the only substance that can exist in all three phases
in the atmosphere. The change of phase of the water is an important
energy source for storms and atmospheric circulation patterns. The
change of phase of water also affects the buoyancy of air, which is
important in cloud and precipitation formation.
- Water vapor is the source of all clouds and precipitation. The
potential for cloud formation and dissipation depends on the amount of
water vapor in the atmosphere.
- The amount of water in the atmosphere is an important factor that
determines the rate of evaporation. Evaporation is important to many
forms of plant and animal life. Human comfort is a function of
temperature, humidity, and wind speed.
- Water vapor is a principle absorber of shortwave and longwave
radiant energy. It is the most important greenhouse gas.
Reports of current weather conditions often include the
dew point temperature
and the relative humidity.
These are just two of several ways to express the amount of water vapor
in the atmosphere.
You can explore the relationships
between dew point temperature and relative humidity.