Transcript Weather - Jefferson Township Public Schools

Weather
What is weather?
The condition of the air (or
atmosphere) at a given location at
a given time
Climate
“Typical” weather in region; the average weather
or the regular variations in weather in a region
over a period of years
• includes temperature, air pressure, humidity,
days of sunshine, etc...
• drastically affected by water & mountains
– coastlines have cooler summers and warmer winters
– mountains greatly slow down winds and weather
Atmosphere
Blanket of air surrounding the earth
Air – the mixture of gases, mainly nitrogen
and oxygen, that forms the Earth’s
atmosphere
•
78% Nitrogen
•
21% Oxygen
•
1% Argon
•
1% Other stuff : Carbon dioxide, water
vapor, ozone, dust, ash, smoke, etc.
Structure of
the
Atmosphere
Lower Layers
Troposphere – the layer of the atmosphere that is
closest to the earth’s surface, where all weather
phenomenon occurs.
8 km thick at the poles
16 km thick at the equator;
(air temperature normally decreases with height)
Stratosphere - upper layer of air 8 - 16 km to
about 50 km and top of the stratosphere
contains the ozone layer; almost completely free
of clouds.
Middle and Upper layers
Mesosphere – the layer of air, 50km to 80km
where temperature begins to decrease with
height, mainly because ozone in the
stratosphere absorbs energy from the sun,
principally ultraviolet radiation
Thermosphere - where air temperatures can
exceed 1000° C (1800° F), 80km to 9600 km,
primarily due to oxygen absorbing the sun’s
energetic rays
Upper-Upper layers
Ionosphere – the region within the
atmosphere containing ionized molecules,
layers of ionized air in the atmosphere
extending from almost 60 km above the
surface of the earth to altitudes of 1000 km
and more.
Exosphere - The region beyond the
thermosphere, which extends to about
9,600 km, the outer limit of the
atmosphere.
Conditions of the Air
Temperature – amount of hotness or coldness
relative to something else
•Thermometer – an instrument that measures
relative hotness or coldness
•Dew Point temperature – The temperature at
which air becomes saturated
•Temperature scales:
1°C = 1.8°F
or
1°F = 5/9 ° C
Heat transfer
• Conduction – the movement of heat from
molecule to molecule
• Convection – the movement of heat by
warm and cold currents
• Radiation – the release and transfer of
energy in wavelengths of heat and light
How is the atmosphere is heated?
Draw
Draw on back of notes
Pressure
Air pressure - the downward pressure exerted by
the weight of the overlying atmosphere or the
“weight” of the atmosphere per unit AREA.
• Barometer – an instrument used to measure air
pressure
Measured in inches of
mercury in a column
• Or millibars (metric
conversion)
• Average air pressure
at sea level is 1013 millibars
Water in the atmosphere
Water Vapor
• Humidity – the amount of water vapor in
the air
• Relative humidity – the actual amount of
water vapor in the air compared to the
greatest amount the air can hold
Precipitation
water or ice that condenses in the air and falls
to the ground as:
• Rain- liquid water that falls to the ground
• Snow - ice crystal flakes; water vapor in the
atmosphere that froze into ice crystals and falls
to the ground in the form of flakes
• Sleet -partially melted grains of ice
• Hail - pellets made of layers of ice and snow
• Freezing rain –rain that freezes into ice as it hits
the ground
Evaporation
the process of changing
from liquid to gas;
molecules in a liquid
state GAIN energy to
change into a gaseous
state
(latent heat energy is the
stored in molecules
through evaporation)
Evaporation
DRIVES
the water
cycle
Condensation
• the process of changing from gas to liquid;
molecules in a gaseous state that LOSE
energy to change into a liquid state.
Clouds
• a visible mass of dense water vapor or ice
suspended in the atmosphere; formed by
surface heating & convection and/or warm
air lifted by rising over mountains
Wind
Air moving at a speed fast enough to be noticed…
• Low pressure – air is de-compressed (allowed to
expand) and sucks air toward.
• High pressure – air is compressed (contracted)
and flows away.
high pressure moves to low pressure
Winds are named by the direction they come
FROM
Instruments:
•
Weather Vane – measures wind direction
•
Anemometer – measures wind speed
LOCAL WINDS: Sea breeze
Sea breeze
wind blowing from sea to land during the
day when the sun warms the land faster
and cool air from above the water forces
the warm air above the land to rise
Draw diagrams
LOCAL WINDS: Land Breeze
LOCAL WINDS: Land Breeze
wind blowing from land to sea at night
because the land cools faster than the sea
Draw diagrams
• Draw diagrams
• High pressure – air is compressed
(contracted) and flows away.
• Low pressure – air is de-compressed
(allowed to expand) and sucks air toward.
– Add the Coriolis Effect and you get ‘cyclonic’
and ‘anticyclonic’ flow.
Coriolis Effect
the effect of Earth’s rotation on movement
of air masses
• http://www.youtube.com/watch?v=_36MiCUS1ro (people on turn
table)
• http://www.youtube.com/watch?v=BPNLZyBNPTE&feature=fvwrel
• http://www.youtube.com/watch?v=mcPs_OdQOYU
• http://www.youtube.com/watch?NR=1&v=Kk7sXkzmtp0&feature=en
dscreen
• http://www.youtube.com/watch?v=49JwbrXcPjc&feature=related
• http://www.youtube.com/watch?v=DHrapzHPCSA – hadley cells
(belts)
• http://www.youtube.com/watch?v=KadsPCOudt0&feature=fvwrel belts
Coriolis Effect on a Synoptic Scale
• Low pressure… air moves:
– Up
– In
– Counter clockwise
• High pressure … air moves:
– Down
– Out
– Clockwise
Global Winds
Draw next page
Air Mass
A large region of air with similar properties
throughout (ie. temperature, humidity)
Major Air Masses
•
•
•
•
•
cA – Continental Artic – dry, very cold
cP – Continental Polar – dry and cold
cT – Continental Tropical – dry and warm
mP – Maritime Polar – moist and cold
mT – Maritime Tropical – moist and warm
•
Draw next page
http://www.youtube.com/watch?v=UmyfkXSFiZA&feature=related
Relative Humidity
Comparison of the specific humidity and the
maximum amount of water vapor that the air can
hold at a given temperature and pressure
 Unit is in percentage = %
Relative humidity = specific humidity X 100%
maximum capacity
100% Rel. Hum. – saturated air
0% Rel. Hum. – dry air
Psychrometer
Dry air - greater evaporation
- greater cooling
- greater the difference in the 2
temperatures
High humidity – no evaporation (saturated air)
- temperatures of the 2 bulbs
will be the same or very close
Psychrometer
 Instrument to
measure humidity
 Dry bulb – measures
air temp.
 Wet bulb – has a
water soak wick
around the bulb –
water evaporates –
cools the air
• As a parcel of air rises up the windward side
of a mountain range, the water vapor in the
air condenses to liquid water and creates
clouds and precipitation.
http://www.youtube.com/watch?v=GJR893xiTr0&feature=related
Rain Shadow (Orographic Lifting)
• When the air begins to flow over the mountain
and down the leeward side of the mountain, it is
dry (lost all of its moisture).
• As the cool air descends, it heats and
compresses (increased pressure), reducing its
possibility of precipitation.
Front
the boundary between two different air masses
– Cold front – a front that moves so that cold air
replaces a warmer air mass
– Warm front – a front that moves so that warm air
replaces a cooler air mass
– Occluded front – a front formed when a cold front
overtakes a warm front
– Stationary front – a front that is not moving
– Polar front – the low pressure zone where polar and
tropical air masses meet
• Manifestation of low
pressure:
Jet Stream
• Jet streams are fast flowing, narrow air currents found in
the atmosphere. The main jet streams are located near
the tropopause and the stratosphere.
http://en.wikipedia.org/wiki/Jet_stream
Jet Stream
http://www.youtube.com/watch?v=CgMWw
x7Cll4&feature=fvwrel
http://www.youtube.com/watch?v=CgMWwx
7Cll4&feature=related
Greenhouse effect
the ability of the atmosphere to let much
sunlight in, but little infrared radiation
(heat) to escape.
Greenhouse effect
Greenhouse gasses: carbon dioxide (CO2),
water vapor, methane (CH4), nitrous
oxide, hydrochlorofluorocarbons, or
HCFCs, & chlorofluorocarbons or CFC’s;
CFC’s are chemicals used in refrigerators,
air conditioners, etc. and aerosol spray
cans that destroy ozone molecules
Causes of the Greenhouse effect
• burning oil, natural gas and coal
(increasing CO2 levels)
• deforestation - burning of cleared forests
release more CO2; no trees to convert
CO2 to oxygen
• Air Pollutant – any
harmful matter
added to the air
• Ozone – a threeatom form of
oxygen that absorbs
ultraviolet sunlight
http://ozoewatch.gsfc.nasa.gov/monthly/mo
nthly_1990-07.htmln
• What
everything
means 
For wind direction –
this example is a NE
wind (going to the
SW) and the speed
is 20 knots
Warm front
•
Cold front 
 Occluded
front
• Unequal heating – currents
• http://www.youtube.com/watch?v=KadsPC
Oudt0&feature=fvwrel
• Collapsing (large) can
• http://www.youtube.com/watch?v=JsoE4F
2Pb20&feature=related
• http://www.youtube.com/watch?v=UySN5j1ogk&feature=related
http://kids.britannica.com/thund
erstorms_tornadoes/ocliwea12
4v4.html