Download Chapter 16 Section 1 Outline

Chapter 16 Section 1 Outline
What is Weather?
I. Weather Factors
A. Refers to the state of the atmosphere at a particular time and place.
1. Describes conditions such as:
a) Air pressure
b) Wind
c) Temperature
d) Amount of moisture in atmosphere
B. The Sun provides almost all Earth’s energy
1. Energy from the Sun evaporates water into atmosphere to form clouds.
2. The Sun is the source of heat energy.
3. Air and water heat differently, which causes uneven heating of earth’s atmos.
4. Heat is distributed by air and water currents.
5. Weather is the result of heat and Earth’s air and water.
C. Air Temperature
1. Air is made up of molecules that are always moving randomly, even with no
wind.
2. Temperature is the measure of the average amount of movement/motion of
molecules.
3. When temp is high…molecules move rapidly and it feels warm
4. When temp is low…molecules move less rapidly and it feels cold.
D. Wind
1. Air moving in specific directions is called wind.
2. When Sun warms air, air expands and becomes less dense and has low
atmospheric pressure.
3. Cooler air is denser and tends to sink and has high atmospheric pressure.
4. Wind results b/c air moves from regions of high pressure to regions of low
pressure.
5. Instruments to measure wind
a) Wind vane and/or wind sock-measures direction
b) Anemometer measures wind speed
6. Humidity
a) The amount of water vapor present in the air.
b) Humidity varies
(1) At warmer temps-molecules of water vapor in air move quickly
and don’t easily come together.
(2) At cooler temps, molecules in air move more slowly and tend to
stick together and form droplets of liquid water called condensation.
(3) When enough water vapor is present in air for condensation to take
place, the air is saturated.
7. Relative Humidity
a) The measure of the amount of water vapor present in the air compared to
the amount needed for saturation at a specific temperature. Example: If
forecaster says, the relative humidity is 50%, then it means that the air
contains 50% of the water needed for the air to be saturated.
8. Dew Point
a) The temp at which air is saturated and condensation forms is the dew
point.
b) When the temp drops, less water vapor can be present in air.
c) The dew point changes with the amount of water vapor in the air.
9. Forming Clouds
a) Clouds form as warm air is forced upward, expands, and cools.
b) As air cools, the amount of water vapor needed for saturation decreases
and relative humidity increases.
c) When relative humidity reaches 100%, the air is saturated.
d) Water vapor beings to condense in tiny droplets around small particles of
dust & salt.
e) Billions of droplets form a cloud.
10.Classifying Clouds
a) Classified by shape and height.
b) Shape and height vary with temperature, pressure, and amount of water
vapor.
11.Shape
a) Stratus-smooth, even sheets or layers at low altitude
b) Cumulus-puffy, white clouds, often w/flat bases
c) Cirrus-high, thin, white, feathery clouds made of ice crystals
12.Height
a) Cirro-high clouds
b) Alto-middle elevation clouds
c) Strato-low clouds
13.Nimbus-“dark rain cloud” clouds that are dark and so full of water that sunlight
can’t penetrate.
a) Cumulonimbus-rain or snow thunderstorm clouds
b) Nimbostratus-layered clouds that can bring, long, steady rain or snowfall
14.Precipitation
a) Raindrops can vary in size due to strength of updrafts
(1) Strong updrafts create large droplets
(2) Dry air can evaporate drops into smaller drops
(3) Air temp determines whether water forms rain, snow, sleet, or hail
(4) Drops falling in above freezing create rain
(5) Below freezing causes water vapor to change directly to solidscrystals/snow
(6) Sleet forms when raindrops pass through a layer of freezing air
b) Hail is precipitation in the form of lumps of ice
(1) Forms in cumulonimbus clouds
(2) Form when ice pellets are tossed up and down by rising and falling
air
Cloud Types in the Troposphere