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Atmospheric Forces:
Weather and Climatology
Mr. Ross Brown
Brooklyn School for Law and
Technology
How do we understand the weather?
• 4 January 2015
• Do now: Take out your Reference Tables.
– What is the dewpoint when the dry-bulb
temperature is 24°C and the wet-bulb
temperature is 15°C?
a)
b)
c)
d)
8°C
-18°C
36°C
4°C
Air Mass
• Large, uniform temperature and moisture
content
• Types:
– Polar (P) cold
– Tropical (T) warm
– Maritime (m) oceans
– Continental (c) land
Air Masses
• Combinations
– Maritime Polar (mP)
– Maritime Tropical (mT)
– Continental Polar (cP)
– Continental Tropical (cT)
North American Air Masses
Air Masses
An airmass originating over the North Pacific Ocean
would most likely be
a)
b)
c)
d)
continental polar
continental tropical
maritime polar
maritime tropical
On a weather map, an airmass that is very warm
and dry would be labeled
a)
b)
c)
d)
mP
mT
cP
cT
Fronts
• Air masses of different densities meet along a
Front.
• Warm front: warm air overtakes cool air.
Warm air rises over cool.
Fronts
• Cold front: cold air mass overtakes a warm air
mass, lifting the warm air. May cause storms.
A big storm ahead of the front is a squall.
Fronts
• Stationary front: two air masses meet but
neither is displaced
Fronts
• Occluded front: fast cold front completely lifts
warm front and keeps it high in the
atmosphere.
How do Hurricanes form?
•
•
•
•
Windspeed >120 km/ hour
Spiral toward intense low-pressure center
Warm, moist air over ocean rises
Moisture condenses, releasing heat energy
Wind patterns
Wind patterns
• The arrows on the diagram below represent surface wind directions on a
weather map. The points represent the locations of four weather stations
in the Northern Hemisphere. Which weather station probably has the
lowest air pressure?
•
•
•
•
A
B
C
D
Forecasting the weather
Forecasting weather
This question may require the use of the Earth Science Reference
Tables.
The station model below shows the weather conditions at
Massena, New York, at 9 a.m. on a particular day in June.
What was the barometric pressure at Massena 3 hours earlier on
that day?
a)
b)
c)
d)
997.1 mb
999.7 mb
1003.3 mb
1009.1 mb
The weather map
• Isobars: lines connecting points of equal
atmospheric pressure. Lines closer together
mean faster winds.
Heat Energy and Water
• Water changes state from icewatersteam
and back again
• Absorbs and releases heat during this process
Sublimation
• The change from ice directly to steam or
steam to ice. For example, steam going out on
a winter’s day.
Humidity
• Humidity: Water vapor in the atmosphere
• When the air holds as much water vapor as it
can, it is saturated
• As temperature rises, ability to hold water
vapor rises
• Relative humidity: ratio of water vapor in the
air to amount that could be held (%)
How do we measure relative
humidity?
• Psychrometer: instrument with 2
thermometers, one with a wet wick
• Dew point: temperature at which water vapor
begins to condense
Atmospheric Pressure
• Gravity pulls atmospheric gases toward the
Earth’s surface
– 99% of mass of atmospheric gases are within 32
km of surface
– A reading of 1 atmosphere = average atmospheric
pressure at sea level
– 1 millibar (mb) equals 0.001 of standard
atmospheric pressure
How do we measure atmospheric
pressure?
• Barometer
– Mercurial barometer: atmospheric pressure
presses on liquid mercury in a glass tube. We read
how high it gets pressed.
How do we measure atmospheric
pressure?
• Aneroid barometer: Sealed container with air
removed. As pressure increases, sides of
container bend inward.
Layers of the Atmosphere
• Troposphere: closest to Earth’s surface
– Up to ~ 10 km
• Stratosphere: troposphere to 50 km
– Ozone is contained here
• Mesosphere: stratosphere to 80 km
• Thermosphere: above
Layers of the Atmosphere