Transcript (water vapour).

The Three States of Water
Water can exist in three states: solid (ice), liquid (water), and
gas (water vapour).
Water exists in the air in the form of water vapour, clouds, fog,
and precipitation.
The Three States of Water
A schematic diagram of the three states of water. Arrows show the ways that any
one state can change into either of the other two states. Heat energy is absorbed
or released, depending on the direction of change.
Global Water Balance
Since our planet contains only a fixed amount of water, a global
balance must be maintained among flows of water to and from the
lands, oceans, and atmosphere.
This balance also controls the proportion of water found in the
different reservoirs of the hydrosphere.
The oceans and glaciers contain most of the water. The
remaining freshwater, upon which we are so dependent,
comprises the least.
Global Water Balance
Figures give average water flows in and out of world land areas and world oceans.
Values are given in thousands of cubic kilometres. Global precipitation equals
global evaporation.
Humidity
The amount of water vapour present in the air is called humidity. Specific
humidity is a measure of the actual quantity of water vapour held by the air.
Relative humidity compares the amount of water vapour present to the
maximum amount that the air can hold at that temperature, expressed as a
percentage.
Humidity
The maximum specific humidity of a mass of
air increases sharply with rising temperature.
Relative humidity changes with temperature
because the capacity of warm air to hold water
vapour is greater than that of cold air. In this
example, the amount of water vapour stays the
same, and only the capacity changes.
The Adiabatic Process
Physicists use the term adiabatic process to refer to a heating or
cooling process that occurs solely as a result of pressure change.
That is, the change in temperature is not caused by heat flowing into
or away from a volume of air, but only by a change in pressure on a
volume of air.
*See the Animation on the Adiabatic Process found on WileyPLUS or your text's website.
The Adiabatic Process
A schematic diagram of adiabatic cooling
and heating that accompanies the rising and
sinking of a mass of air. When air is forced to
rise, it expands and its temperature
decreases. When air is forced to descend, its
temperature increases.
Adiabatic decrease of temperature in a rising
parcel of air leads to condensation of water
vapour into water droplets and the formation
of a cloud.
Clouds
A cloud is made up of water droplets or ice particles suspended in air.
Clouds
Clouds are grouped into families on the basis of height. Individual cloud types are
named according to their form.
Types of Clouds
Cirrus in Parallel Bands
Altostratus Layer
Stratocumulus Clouds
Cirrocumulus Clouds
Altocumulus Clouds
Cumulus Clouds
Precipitation
Precipitation can form in two ways:
1) Water droplets condense, collide, and coalesce into
larger and larger water droplets that fall as rain. This is
referred to as coalescence.
2) Ice crystals form and grow in a cloud that contains a
mixture of both ice crystals and water droplets. This occurs
where the cloud temperature is below zero degrees Celsius,
but despite that some droplets are still liquid in form.
Precipitation
Growth of raindrops is called coalescence.
Types of Precipitation
The processes responsible for precipitation in the
atmosphere create different forms of precipitation.
Rain falls from warm clouds where saturated
air has risen quickly and cooled, leading to
condensation. Snow, however, forms in cool
clouds where ice crystals collide with super
cooled water droplets. If they fall through air
that is below freezing, they remain as snow
flakes. If the air is above freezing, they begin
to melt and fall as sleet. Hail falls from tall
cumulonimbus clouds associated with
thunderstorms. Large hailstones grow as the
updrafts in the clouds successively add layer
upon layer of condensing water.
Orographic Precipitation
In orographic precipitation, through-flowing winds move moist air up and
over a mountain barrier. The term "orographic" means related to the
mountains.
*See the Animation on Orographic Precipitation found on WileyPLUS or your text's website.
Convectional Precipitation
In convectional precipitation, unequal heating of the
surface causes an air parcel to become warmer and
less dense than the surrounding air. Because it is
less dense, it rises. As it moves upward, it cools, and
condensation with precipitation may occur.
*See the Animation and Video Clip on Convectional
Precipitation (Thunderstorms) found on WileyPLUS or
your text's website.
Successive bubbles of moist condensing air push upward in the thunderstorm cell. Their
upward movement creates a corresponding downdraft, expelling rain, hail, and cool air
from the storm as it moves forward.