Download Study Guide for Weather

Study Guide for Weather
1. Water Cycle – Understand that the water cycle is a continuous process. Know the
following terms and where they fit into the water cycle:
•Evaporation
•Transpiration
•Condensation
•Precipitation – Rain, snow, sleet, and hail
•Infiltration
•Percolation
•Groundwater
•Runoff
•Aquifers
2. Layers of Earth’s Atmosphere – Understand that when it comes to weather, the
troposphere is where it happens, with some exception – the
stratosphere is where upper level winds called the jet stream flow
in a west to east winding fashion and can greatly influence our
weather here in North America.
•Also be aware that temperature decreases as you increase in
altitude in the troposphere. This leads to cooling of warm, moist,
rising air which in turn leads to condensation and cloud formation.
•Understand that it is the Ozone Layer that is responsible for the
increase of temperature with an increase in altitude in the
stratosphere.
•The Ozone layer is made up of O3 Molecules which absorb most
of the harmful ultraviolet (UV) energy from the sun. This protects
us from radiation that causes sunburn, skin cancer and even genetic
damage to some organisms. Understand that CFC’s
(Chlorofluorocarbons), a manmade compound used in Styrofoam
production, refrigeration and as a propellant in aerosol cans are
know to destroy Ozone molecules. The chlorine in CFC’s break
off of the molecules of CFC’s and attack Ozone, rendering it
useless as an absorber of UV energy. The result of this destruction
has been the thinning and gradual disappearance of the ozone
layer. The Montreal Protocol was an international treaty that
banned the use of CFC’s in most countries. The Ozone layer is
repairing itself as a result of this ban.
•The Greenhouse Effect – Know that greenhouse gasses –
especially Carbon Dioxide, Nitrogen Oxides and methane are good
to an extent as they help the planet stay warm enough for us to live
and thrive, but that too much of a good thing (in other words, too
much greenhouse gas) is not good.
•Increases in greenhouse gasses are believed by many to be the
cause for rising global atmospheric temperatures which could lead
to extreme changes in weather patterns and melting of polar and
glacial ice. Humans have greatly increased the amounts of these
gasses in our atmosphere by burning of fossil fuels and through
dramatic increases in cattle production. This process is known as
global warming.
• Study the greenhouse effect diagram and understand how the
process works. Basically, short wavelength solar energy passes
through our atmosphere and warms the surface of the Earth. The
Earth then emits long wavelength infrared (heat) energy which is
trapped by greenhouse gasses, much like a blanket or clothing
traps heat near your body. This keeps us warm, but like too much
clothing or too many blankets, too much greenhouse gas traps too
much heat making us too hot.
3. Temperature – Know that temperature is a measurement of the amount of heat
energy in a substance. In other words, how fast the molecules in a
substance are moving.
• Be able to calculate/convert temperature in degrees Fahrenheit to
Celsius and from Celsius to Fahrenheit using the following
Formulas:
Fahrenheit to Celsius
and
Celsius to Fahrenheit
(°F-32) x 0.556 =°C
(°C x 1.8) + 32 = °F
• Also remember that degrees Kelvin, the scale used by many
scientists, incorporates the notion of absolute zero (the
hypothetical temperature at which all molecular motion ceases).
4. Dew Point – Recall that dew point (or dew point temperature) is the temperature
at which the air is saturated (cannot hold any more water vapor)
and condensation begins.
• Also recall that a psychrometer is the instrument meteorologists
use to find the dew point. The psychrometer has two
thermometers. One is dry and the other is wet. Evaporation
enables the wet thermometer (called the wet bulb) to cool and will
therefore be cooler than the dry bulb.
5. Wind Chill and Heat Index – Recall that wind chill is a calculation that involves
temperature and wind speed. Wind chill is used to describe the
temperature that the air actually feels (colder than actual measured
temperature) due to wind blowing heat away from your body.
•Also recall that Heat Index is a calculation that involves
temperature and humidity. Heat index is used to describe the
temperature that the air actually feels (hotter than actual measured
temperature) due to high humidity preventing evaporation which is
a normal cooling process.
6. Pressure a.) Pressure gradients (two areas with different pressures) will try to
equalize.
b.) Pressure ALWAYS moves from High pressure to Low pressure!!!
c.) Pressure gradients cause wind. The steeper the gradient (greater the
difference) the stronger / faster the winds.
d.) Low pressure areas are areas where warm air (less dense than surrounding
air) rises. The result of low pressure is the formation of clouds and are
often associated with precipitation.
e.) High Pressure areas are areas where cooler, dry air (more dense than
surrounding air) sinks. The result of high pressure is clear skies and often
cooler temperatures.
7. Clouds A. How do clouds form?
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Key terms: EVAPORATION, CONDENSATION, DEW POINT,
CLOUD DROPLETS
First, EVAPORATION takes place as the Suns energy energizes water
molecules from plants, puddles, streams, rivers, lakes, oceans and soil.
The air (warm, moist air) is less dense than cooler, dryer air, so it rises up into
the atmosphere.
As air rises, it cools and expands (due to less pressure). This is known as
adiabatic cooling.
At some elevation, the warm, moist air reaches it’s DEW POINT ( the
temperature at which gas turns back to liquid) and CONDENSATION occurs
around tiny particles of dust.
These tiny droplets of water (known as CLOUD DROPLETS) form clouds
when millions of these droplets cluster together.
As these droplets bump into one another, the droplets stick together and get
larger. When the get too big and heavy to remain suspended in the
atmosphere, they fall as precipitation.
Precipitation is either rain, snow sleet or hail.
B. What determines the type of precipitation that falls?
 Precipitation type, for the most part, depends on the temperature of the
atmosphere the droplets fall through.
 Droplets that fall through temperatures above freezing fall as rain.
 Snow forms when air temperature is below freezing and water vapor turns
directly into snow.
 If snow flakes pass through a layer of warm air and melt, then pass through a
layer of below freezing air, they re-freeze turning into sleet.
 Hail forms in cumulonimbus clouds where air currents are very active. The
water droplets are blown up into the cloud where they freeze, then they fall
down into warmer air nearer the bottom of the cloud where a new layer of
water sticks to the small ice pellet. This mixture of ice and water then blows
back up into the cloud where it freezes again. This process is repeated several
times and the ice pellet grows until it is to large to be suspended by the strong
winds that are present inside of the cumulonimbus cloud. At this point, the ice
(known as a hailstone) falls to earth.
C. What are the three main types of clouds?
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CUMULUS clouds are the puffy white clouds that often accompany fair
weather. They can grow into much taller and more troublesome
cumulonimbus clouds that bring heavy rain, strong winds, thunder and
lightning, even hail and tornadoes.
 STRATUS clouds are like blankets that cover the sky. These clouds
accompany dreary weather and can bring rain showers.
 CIRRUS clouds are found at really high altitudes. They are the thin, wispy
ice clouds that usually occur on nice days. Watch for these clouds to bunch
up and increase in number, this indicates coming storms.
7. Thunderstorms –
A. Remember that thunderstorms occur in association with
cumulonimbus clouds. They are most often associated with cold fronts and or
occluded fronts where warm moist air is rapidly forced upward by advancing cold
air resulting in the formation of cumulonimbus clouds. Also recall that mountains
can be responsible for warm, moist air being rapidly forced upward (this is the
case in the pacific northwestern United States and results in temperate rain forests
in the state of Washington). Three ingredients are associated with thunderstorms:
moisture, unstable air and lift.
B. Lightning occurs when positive and negative charges separate in clouds
(positively charged ions move to the tops of cumulonimbus clouds while negative
charges build up at the bottom). As ice crystals brushing past one another is
believed by many to cause this separation of charges. Cloud to ground lightning
is due to a buildup of positive charges on the ground which are attracted to the
negatively charged cloud bottom. When the potential difference is great enough,
the electrons from the cloud move toward the ground creating a pathway for the
electricity to flow. Thunder is sound waves that are produced by the air rapidly
expanding away from the intense heat generated by the lightning. As the air
molecules race back together, tremendous sound waves are produced.
C. Hail that is associated with severe thunderstorms is formed as water droplets
blow upwards in cumulonimbus clouds and freeze, then fall back to the lower
portion of the cloud and pick up more water. This process of moving up and
freezing, then down and gaining more water results in the growth of the
hailstones. Eventually, the updrafts in the clouds are no longer strong enough to
support the weight of the hailstones and they fall to the ground, often causing
significant damage.
D. Severe Thunderstorm Watches and Warnings –
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Severe thunderstorm watches are issued by the National Weather
Service to let people know that the conditions are right for Severe
Thunderstorms (those with winds over 80km/hr and 2cm or larger
hailstones) to develop.
A severe thunderstorm warning means that severe thunderstorms have
actually developed in your area and immediate action is necessary.
The National Weather Services warns people in a severe thunderstorm
to stay indoors away from windows and electrical appliances and to
avoid contact with water as these create significant hazards from
electrical shock and flying debris. If you are outside, you should get
indoors if possible and avoid tall structures such as trees or towers as
they are most likely to attract lightning.
Strong wind gusts called Gust Fronts are the result of tremendous
amounts of air moving as a result of the high volume of falling rain.
They occur in advance of the storm.
Tornadoes & Hurricanes
– Refer to the tornado research questions and the hurricane
research questions that you answered in class.