1. Water in the Atmosphere

2. Characteristics of Water
solid state 0oC or below (appearing as ice, snow, hail and ice crystals)
liquid state between 0oC and 100oC (appearing as rain and cloud droplets)
gas state 100oC or higher. This is an invisible gas referred to as water vapor.

3. Characteristics of Water
energy is either absorbed or released when water changes state
changing from a gas to a liquid is called condensation, energy is released.
Products of condensation is dew, fog, and clouds
condensation slows down the rate at which air cools
changing from a liquid to a gas is called evaporation, energy is absorbed.
Evaporation is a cooling process, heat is absorb by water molecules

4. Humidity Humidity: amount of water vapor present in the air.
Specific Humidity: actual amount of water vapor in the air at a given time or place is.
Expressed as the number of grams of water vapor per kilogram of air.
Saturated: when air can not hold anymore water vapor
condensation equals evaporation.
Amount of water vapor in saturated air is dependent on the temperature.
The warmer the air the more water vapor it can hold.
The water vapor capacity of air roughly doubles for every 11oC rise in temperature.

5. Humidity
Meteorologist report the relative humidity in weather forecasts.
Relative humidity is how near the air is to maximum capacity for holding water vapor.
Relative humidity units is percentage (%)

6. Measuring Humidity
Humidity measured using a psychrometer and a relative humidity chart.
The psychrometer, which works on the principle that evaporation causes cooling.
A psychrometer consists of two thermometers, one dry bulb and one wet bulb.

7. Condensation Condensation is the changing of water vapor to a liquid
night air cools more rapidly and when it cools past the point of saturation, condensation occurs.
Water vapor condensing in the atmosphere forming clouds or fog.
Water vapor condensing on surfaces is called dew.
Dew Point is temperature at which saturation occurs and condensation begins.
The more water vapor in the air the less the air has to cool in order for condensation to begin.

8. Cooling and Condensation
Two conditions are required for condensation to occur:
Condensation nuclei
Air must cool to or below the dew point
Condensation nuclei are usually substances such as salt, sulfate, particles, or nitrate particles.
Condensation nuclei are also required for the formation of ice crystals.
Air may cool or lose heat through the following ways:
Contact with a colder surface
Radiation of heat
Mixing with colder air
Expansion as it rises

9. Cooling and Condensation (cont)
Dew/Frost forms when moist air contacts a colder surface.
Air temp above 0oC dew forms
Air temps below 0oC frost forms
Fog forms when air cools through contact and mixing
Droplets are so small they fall slowly so that the slightest air movement keeps them suspended.
At very cold temperatures fog may consist of ice crystals.
Radiation fog occurs when the nighttime sky is clear and the ground loses heat rapidly (common in humid valleys)
Advection fog occurs when warm moist air blows over a cool surface.

10. Clouds Four types of clouds
Low clouds
Middle clouds
High cloud
Vertical developed clouds
classified based on their altitude and shape.
Cloud names formed from one or more of the five words or word parts:
Stratus or strato – clouds that form in layers
Cumulus and cumulo – clouds that grow upward, puffy
Cirrus and cirro – feathery clouds
Alto – clouds located between 2000 and 7000 meters
Nimbus and nimbo – dark rain clouds

11. CLOUDS

12. Cloud Formation Shape of a cloud shows how the air is moving
Vertical developed clouds form when rising air is lighter than the surrounding air.
condensation level: the atmospheric level at which condensation occurs
Rising air cools to its dew point
Without a steady influx of warm, moist air the cloud will soon evaporate.
clouds stop growing upward when the air in the cloud reaches the same temperature as the air surrounding the cloud.

13. Cloud Formation (cont)
the adiabatic rate is the rate at which air cools.
water vapor releases energy (heat) as it condenses.
released heat is very important to the formation of clouds
Rising dry air cools faster than rising moist air.
Moist air cools more slowly due to the fact that heat is being released by condensing water vapor.
Heat released during condensation can fuel the growth of huge cumulonimbus clouds.

14. Cumulonimbus Clouds
Cumulonimbus clouds form as moist air rises and cools to its dew point (condensation level).
Heat released from the condensation keeps the air rising.
air inside the cloud is warmer and less dense than the air outside.
cumuliform cloud that receives continuous supply of moist air continues to grow until it enters a layer of stable air.
Stable air is where the surrounding air temperature is the same as inside the cloud.

15. Layer Clouds Stratiform or layered clouds form in stable air.
Air cannot easily move up or down in stable air so the clouds spread out horizontally.
Clouds form in stable air in two ways:
Air is forced slowly upward to its condensation level. This happens when air moves up a mountainside or over a layer of colder denser air or a low pressure forces it upward.
Air can cool past its condensation level by radiating heat or mixing with cooler air

16. Predicting Condensation Level
As air that rises temperature and dew point decreases.
condensation level can be determined by knowing the ground temperature and dew point
Knowing the condensation level allows for
predicting at what level clouds will form
predicting how high they will grow.
predicting the severity of a possible storm

17. Precipitation
Precipitation: any form of water that has formed in clouds and has grown heavy enough to fall to Earth.
Water droplets grow by
bumping into and combing with other water droplets.
the larger the droplets the faster they will fall.
temperatures in upper clouds is below freezing
both ice and supercooled droplets form in the clouds
supercooled droplets evaporate and deposits on the ice crystals causing them to grow

18. Kinds of Precipitation
There are several forms of precipitation:
Drizzle, Rain, Snow
Sleet: rain freezes as it falls
Freezing rain: rain freezes as it hits a cold surface
Hail: balls or irregular clumps of ice.
In the summer, frozen precipitation melts before hitting the ground except for Hail.
Hailstones begin as a frozen raindrop or small, dense clump of ice crystals
Strong updrafts cause hailstones until it is too heavy and falls
The stronger the updrafts the larger the hailstones.

19. Where does precipitation occur
rising and cooling moist air major cause of precipitation
the warmer the air is before it rises the more moisture it can hold
the higher air rises the more precipitation it can release
Areas that receive the most precipitation are those where warm moist air rises high in large quantities.
Near the equator due to heating of the land by insolation, causing warmed air to rise. Daily thunderstorms occur in this region
Low pressure areas which cause air to rise and cool to produce precipitation
Areas where moist air often blows across a mountain range,
the windward side receives precipitations as the air rises and cools. It can receiving large amounts of precipitation.
the leeward side the colder and dryer air is sinking and warming so there is little to no precipitation on this side of the mountain range (desert regions occur on the leeward side of a mountain range).

20. Windward and Leeward

21. Global Precipitation