Condensation is the change of water from its gaseous form (water
vapor) into liquid water. Condensation generally occurs in the
atmosphere when warm air rises, cools and looses its capacity
to hold water vapor.
As a result, excess water vapor condenses to form cloud droplets.
The upward motions that generate clouds can be produced by convection
in unstable air, convergence associated with cyclones, lifting
of air by fronts and lifting over elevated topography such as
atmospheric motions in the vertical direction: In meteorology,
convection refers primarily to atmospheric motions in the vertical
direction. As the earth is heated by the sun, different surfaces
absorb different amounts of energy and convection may occur
where the surface heats up very rapidly. As the surface warms,
it heats the overlying air, which gradually becomes less dense
than the surrounding air and begins to rise.
Convergence Associated With Cyclones
extra-tropical and tropical cyclones In extra-tropical cyclones,
surface winds are deflected by friction towards the center of
the low pressure system.
Coupled with divergence aloft, (blue arrows), surface convergence
(red arrows) can generate rising motion (green arrow) that leads
to the condensation of water vapor
boundaries between air masses Fronts are boundaries
between air masses. Depending on the air masses involved and
which way the fronts move, fronts can be either warm, cold,
stationary, or occluded.
In the case of a cold front, a colder, denser air mass lifts
the warm, moist air ahead of it. As the air rises, it cools
and its moisture condenses to produce clouds and precipitation.
Due to the steep slope of a cold front, vigorous rising motion
is often produced, leading to the development of showers and
occasionally severe thunderstorms.
In the case of a warm front, the warm, less dense air rises
up and over the colder air ahead of the front. Again, the air
cools as it rises and its moisture condenses to produce clouds
and precipitation. Warm fronts have a gentler slope and generally
move more slowly than cold fronts, so the rising motion along
warm fronts is much more gradual. Precipitation that develops
in advance of a surface warm front is typically steady and more
widespread than precipitation associated with a cold front.