Download CH. 16 Weather Factors I. Energy in the atmosphere A. Energy from

CH. 16 Weather Factors
I. Energy in the atmosphere
A. Energy from the sun causes weather
1. infrared radiation, visible light and ultraviolet radiation reach Earth’s
surface
a. infrared radiation – longer wavelengths than light are felt as
heat
b. ultraviolet radiation – shorter wavelengths than light give
sunburns, and help skin make vitamin D
2. different gases and particles in the atmosphere absorb different types of
energy
a. dust particles scatter light – reflect it in all directions
1) shorter wavelengths (blue and purple) get scattered
more, making the sky look blue
B. Energy at Earth’s surface – different latitudes receive different amounts of
energy
1. land absorbs light, and gives off energy as heat (infrared)
2. infrared waves can’t pass through CO2, H2O and some other gases
a. they hold in heat – greenhouse effect
b. Earth would get too cold for life at night without the greenhouse
effect
II. Heat Transfer
A. Temperature – measure of amount of motion of molecules in an object
1. measured with a thermometer
2. scale for most of the world is Celsius
a. water freezes at 0oC, and boils at 100oC
3. only the US uses Fahrenheit
a. water freezes at 32oF, and boils at 212oF
B. Methods of heat transfer
1. radiation – electromagnetic waves that can go through space
2. conduction – touching molecule bang into each other
a. can’t go through space
b. works best in solids – particles closer together
3. convection – heat transfer in moving fluids – liquids and gases
a. hot fluid rises and cools
b. cooler air gets less dense, then sinks again
(diagram)
III. Winds
A. Caused by differences in air pressure, which are caused by uneven heating of
Earth’s surface
B. Measure wind with an anemometer (picture)
1. wind chill factor – how much cooler wind makes it feel
C. Wind Classifications
1. local winds – in the area around you
a. land heats up faster than water, pavement heats up faster than
forests, etc
b. hot air rises, so air over cool area blows toward the warmer
land – making a convection current
2. monsoons – winds from cool oceans blow into land on hot continents
for the summer season
a. causes lots of rain
D. global winds – steady wind direction over large parts of the Earth
1. Caused by how direct sun rays are making warmer and cooler belts on
Earth
a. Diagram
2. giant convection currents form at certain latitudes on Earth
a. diagram
3. Coriolis Effect – rotation of Earth causes convection currents to curve
a. doldrums – near equator, little wind due to quickly rising hot air
b. Horse Latitudes – 30o north and south of the equator,
cooler air sinks and causes another area of little wind
c. Trade Winds – air from 30o blows toward the equator to
complete the convection current
1) in northern hemisphere wind comes from northeast
2) in southern hemisphere wind comes from southeast
d. Prevailing Westerlies – 30 to 60o in both hemispheres – wind
from the west
e. Polar Easterlies – from pole to 60o in both hemispheres – wind
from the east
E. Jet Stream – about 10 km up, a band of fast wind that moves weather systems
quickly
IV. Water in Atmosphere
A. Humidity – water vapor in the air
1. amount depends on temp. – higher temp can hold more water
2. relative humidity (RH) – percent of water in air compared to max.
amount for that temp.
3. measured with a psychrometer – 2 thermometers that are twirled
together
a. dry bulb thermometer – regular thermometer
b. wet bulb thermometer – has a wetted piece of cloth by the bulb
c. after spinning, find the difference between temp. for the
thermometers, and look on chart to see RH
B. Cloud Formation – as air cools, dissolved water vapor in air condenses and
forms tiny water drops or ice crystals which make up clouds
1. dew point – temp. where condensation begins
2. condensation nuclei – tiny dust particles needed for drops to form
3. more clouds form over mountains because mountains force air to rise,
and as it rises, it cools and can’t hold as much water
a. side of mountain that wind usually blows toward called
windward side – gets more rain
b. side wind blows away from called leeward side – drier
1) most water already fell on windward side
2) air sinks and warms, so can hold moisture
C. Types of Clouds
1. cumulus – white puffy clouds – dry weather
2. cumulonimbus – thunder heads
3. stratus – gray blanket – if thick enough, rains
4. cirrus – high thin whispy made of ice crystals – come before rains
V. Precipitation – rain, snow, sleet, hail
A. how it happens – droplets or crystals in clouds bump together until heavy
enough to fall
B. Types of Precipitation
1. rain liquid water
2. snow – frozen flakey
3. sleet – rain freezes into small pellets as it falls
4. hail – larger pellets of ice from thunder heads
a. winds in cloud carry ice pellet up many times growing more
layers
b. can be as large as baseballs
5. freezing rain – rain onto frozen ground or objects
a. most dangerous for driving – smooth sheet
C. Drought – long time with little or no rain
1. bad for plants – poor crops, high fire danger