The Water Cycle&

The phase ’s of H2O

The hydrologic cycle - simplified

Evaporation – liquid to gas

Rate of evaporation depends on 3 things:

1.Temperature (more temp = more evaporation)

2.Wind (more wind = more evaporation)

3.Humidity (lower humidity = more evaporation)

Evaporation is the process by which water is converted from its liquid form to its vapor form and thus transferred from land and water masses to the atmosphere.

Evaporation from the oceans accounts for 80% of the water delivered as precipitation, with the balance occurring on land, inland waters and plant surfaces.

Humidity – how much water vapor is in the air relative to how much can it hold?

Relative Humidity• How near the air is to its maximum capacity for holding water vapor

• Humidity is measured with a psychrometer, An instrument consisting of a dry-bulb thermometer,a wet-bulb thermometer and a data chart.

Specific humidity – actual amount of water vapor within a parcel of air.

Saturated air

When there is so much water vapor in the air, that the rate of condensation equals the rate of evaporation.

Air is 100% FILLED

CondensationYou should

know:

•When warm air rises, it cools

•Warm air can hold more water vapor than

cool air

• Cool air can hold less water vapor

• • when air cools to the dew point,

water vapor condenses to liquid

Warm Air:

- Rises- Expands- Can hold more water vapor

Cool Air:

- Sinks- Contracts- Can hold less water vapor

Warm vs. Cool air:

Condensationthe process by which water changes from a gas to liquid:

- contact with a colder surface- water vapor in air rises and cools - compression

or through an increase in pressure

The DEW POINT

• A measure of the amount of water vapor that the air contains.

• the closer the dew point to the actual temperature, the higher the

humidity.

• the closer the dew point to the actual temp, the more likely it will

begin to rain.

The temperature at which saturation occurs and condensation begins

Forms of condensation

Fog

Clouds

Dew

Air that contains water vapor may rise, cool and condense forming a cloud.

If this happens at the surface, it is called fog.

Condensation nuclei – microscopic particles on which water vapor condenses to form cloud droplets.

*even when air cools below the dew point, condensation to fog or clouds may not occur if there is no condensation nuclei available.

Remember aerosols?

Melting – phase change of water from a solid to a liquid

Freezing– phase change of water from a liquid to a solid

Deposition

The formation of frost is an example of deposition of water vapor

Sublimation – a solid turns directly into a gas

CO2 sublimates

directly from a solid into CO2

vapor