Download 9th grade ch. 7 and 8 notes

Chapters 6 and 7
Properties of the Atmosphere and Weather Systems
1
Ch. 6: Properties of the Atmosphere
Weather: Short-term conditions of the atmosphere.
Some of these conditions include:
The energy needed to change and maintain weather factors comes from the SUN!
Weather factors:
1. Temperature: (See p. 13 in the ESRTs for a conversion chart from
Farenheit to Celcius to Kelvin.)
2. Air Pressure: (See p. 13 in the ESRTs for the Millibar to Inches of Mercury
conversion chart.)
 Caused by weight of air.
 Measured with a barometer (see fig. 6-5 on p. 143 in the rev. bk.)
 On a weather map, lines that connect points of equal pressure are
called isobars.
Factors that affect air (atmospheric) pressure:
 ALTITUDE: The higher the altitude, the lower the air pressure. Airplanes
need to be pressurized so that there is enough oxygen.
 TEMPERATURE: Low temp. = Higher pressure. High temp. = Lower
pressure. This is how a hot-air balloon works!
 HUMIDITY: The MORE humid the air, the LOWER the pressure!! This is
because water vapor takes the place of N2 and O2, which are heavier than
H20.
3. Moisture in the Atmosphere:
SLING PSYCHROMETER
DEWPOINT
Chapters 6 and 7
Properties of the Atmosphere and Weather Systems
2
RELATIVE HUMIDITY
Why is one of the thermometers in a sling psychrometer WET?
Use p. 145 and 146 in your review book or p.12 in the ESRTs to answer
these questions:
1. If the dry-bulb temperature in a room is 14 Celcius and the difference
between the wet and dry bulbs is 5 Celcius, what is the DEWPOINT?
______ What is the RELATIVE HUMIDITY? _______
2. If the dry-bulb is 14 Celcius and the wet-bulb is 12 Celcius, what is the
DIFFERENCE? ______ What is the DEWPOINT? ______ What is the
RELATIVE HUMIDITY? ______
WIND:
 The wind is measured with an anemometer. (See the drawing on p.151 in
your review book.)
 “Wind” is the result of heat flow by convection.
 Winds ALWAYS blow from HIGH to LOW pressure!!
 A “sea breeze” occurs when cooler temperature (and higher pressure) is
over the water and warmer temps (and lower pressure) is over the land. A
nice, refreshing, cool breeze blows from SEA to LAND.
 A “land breeze” occurs when the land is cooler than the ocean and the winds
blow from LAND to SEA. This happens at night, when the sand has cooled
but the ocean still feels a little warm! (See p. 149 in the rev. bk.)
 Winds blow FASTER when isobars are CLOSE!
 Winds are named for WHERE THEY CAME! For example, if a breeze is
blowing from Watertown towards Syracuse, it would be called a North wind.
Chapters 6 and 7
Properties of the Atmosphere and Weather Systems
3
 Wind paths tend to curve due to the Earth’s rotation. This is called the
“CORIOLIS EFFECT.” Winds curve to the RIGHT in the northern
hemisphere. See figure 6-14 and 6-15 on p. 150.
 Also, there are shifts in wind direction every 30 degrees of latitude!! (see p
14 in the ESRTs.)
 Remember, winds blow from High to Low Pressure.
 The winds cause the ocean currents to move. The ocean currents also
curve due to the Coriolis Effect. (See p 5 in the ESRTs.)
 How did ancient explorers get to America? How did winds and ocean
currents play a part in early exploration?
Weather Variables and How They Are Related:
Daily temperature changes affect pressure, wind speed and relative
humidity.
 Warmer air = lower pressure and cool air = high pressure
 Winds blow from high to low pressure – therefore unequal heating =
unequal pressure = WIND!
 When the air is warmer, it can hold more water. Cold air can hold
LESS water. As temp increases, relative humidity decreases. As temp
decreases, relative humidity increases. If relative humidity hits
saturation (100%), “dew” will form. This “dew” may also be in the form
of frost or fog!
 When water ENTERS the atmosphere due to EVAPORATION, it
makes the dew point INCREASE.
 When water LEAVES the atmosphere due to CONDENSATION, it
makes the dew point DECREASE.
Clouds and Precipitation:
Clouds are created when air RISES, COOLS BELOW ITS DEW POINT, and
WATER VAPOR CONDENSES.
Why does air “rise”?
 Air that is lower in density will rise above higher density air. (Warmer
temps and/or moister air will result in lower density!)
 Cold air will force warm air to rise.
 Air can be forced to rise if it is pushed up a mountain or plateau.
Chapters 6 and 7
Properties of the Atmosphere and Weather Systems
4
Why does air cool and form clouds as it rises?
 Air expands as it rises due to the lower air pressure higher in the
atmosphere. When air is allowed to expand, its molecules are farther
apart. These molecules have less heat energy. (Feel a CO2 cartridge
right after it has been used!)
 When air cools below its dew point, tiny droplets of condensation cling to
“condensation nuclei” – little bits of dust, salt crystals, etc. in the air.
Clouds can not form if the air is PERFECTLY clean! Rain helps clean the
air of pollutants because raindrops surround these condensation nuclei.
What is Precipitation?
When cloud droplets gather together, they may get large enough to start to
fall through the air.
 Most clouds are so high up that precipitation starts out as snow – even
in summer!
CHAPTER 7: WEATHER SYSTEMS
How does energy get into the atmosphere?
 Most of earth’s energy comes from the sun in the form of
electromagnetic radiation.
 See p. 163-164 in your review book or p. 14 in the ESRTs for the
electromagnetic spectrum.
 Which type of wave has the shortest wavelength? ___________
 Which has the longest? ___________
 Where does MOST (75%) of the sun’s energy that reaches the earth
get used for?
 How can you INCREASE the rate of evaporation?
 How can you DECREASE the rate?
The 3 states of water:
ICE  LIQUID WATER  WATER VAPOR
(graph from p. 165 in rev. bk.)
 1 gram of ice requires 80 calories to melt (heat of fusion).
Chapters 6 and 7
Properties of the Atmosphere and Weather Systems
5
 1 gram of liquid water requires 540 calories to evaporate (heat of
vaporization).
 1 gram of liquid water requires 1 calorie to rise 1 degree Celcius, as
long as it remains a liquid.
 1 gram of ice or water vapor requires .5 calorie to rise 1 degree
Celcius, as long as it remains ice or vapor.
 So… which of the above processes took the most energy (calories?)
 The above processes will RELEASE energy (calories) if their
temperatures go down or if the phase change goes from gas to liquid
or liquid to solid.
 When fog is created, water droplets form from vapor – water goes from
a GAS to a LIQUID. For every 1 gram of fog, 540 calories of heat is
released into the air. So, fog can release a lot of energy. Sometimes it
is enough to significantly melt snow!!
Sometimes water vapor can DIRECTLY change to ice or snow – this is
called “deposition.”
Sometimes ice or snow can change DIRECTLY to vapor – this is called
“sublimation.”
Synoptic Weather Maps:
These maps put a lot of weather info onto one map. This info comes form
“weather stations.” See p. 168 in the rev. bk or p.13 in the ESRTs for an
example of a weather station model.
REMEMBER:
 Don’t use any labels!!
 The temperatures are in FARENHEIT!
 Air pressure is in MILLIBARS and must be converted from the
abbreviated form:
If the first digit is 0,1,2,3,or 4 – put a “10” in front and a decimal between the
last two digits.
If the first digit is 5,6,7,8 or 9 – put a “9” in front and a decimal between the
last two.
Chapters 6 and 7
Properties of the Atmosphere and Weather Systems
6
Air Masses:
Air masses are described by their TEMPERATURE and MOISTURE
CONTENT.
c = continental
m = maritime
T= tropical
P = polar
A = arctic
Describe the characteristics of these air masses:
cP
cT
mT
mP
cA
Where might these air masses have originated?
Predicting the Weather:
 Most weather systems in the continental U.S. move from WEST
towards the EAST, so Chicago’s weather today may be OUR weather
in a day or two.
 Meteorologists look for the presence of “high” and “low” pressure
areas:
 High pressure (DIVERGENCE) brings sinking air, few clouds (clear
skies) and dry conditions.
 Low pressure (CONVERGENCE) brings rising air, many clouds and
moist conditions.
 ALSO: low pressure systems pull in other air masses which brings
different “fronts” together, leading to often stormy conditions.
Define: Front:
Living With Natural Hazards:
 Thunderstorms: Stay away from high ground; metal objects; water.
 Tornadoes: STRONGEST winds! They are usually small, and last for
less than an hour.
 Hurricanes: Not as strong as tornadoes, but MUCH larger and longer
lasting. Coastal flooding from the storm surge is especially hazardous.