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WEATHER
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Heating the Earth
Air pressure
Winds
Moisture in the Air
Clouds
Weather Instruments
Weather Patterns
Predicting the Weather
Heating The Earth
The atmospheric factors
that interact to cause
weather are:
•W (winds)
•H (heat energy)
•A (air pressure)
•M (moisture)
Heat Transfer in the
Atmosphere
• 1. Conduction – direct
transfer of heat energy from
one substance to another.
Ouch!
• 2. Convection – the transfer of heat
energy in a fluid (gas or liquid)
• 3. Radiation – transfer of heat energy
through empty space.
Greenhouse Effect
• Ultraviolet (UV) rays from the sun
pass easily through the atmosphere
to the Earth.
However, infrared rays
cannot
pass back out as easily.
It
helps the Earth
keep nice
and warm!
Without the Greenhouse
Effect the Earth would be a
frozen tundra!
Temperature Variations
• The Earth has varying
temperatures due to the
different angles at which the
sun’s rays strike the Earth.
COLDER
TEMPERATURES
HOTTEST
TEMPERATURES
Air Pressure
Factors That Affect Air
Pressure
• W (water vapor)
• E (elevation)
• T (temperature)
Water Vapor
• Moist air is less dense than dry
air. This is because a water
molecule has less mass than
an oxygen molecule.
• The MORE water vapor in the
air…the
Elevation
• The higher the elevation (height
above sea level), the less
dense (thinner) the air.
• The GREATER the elevation
above sea level, the LOWER
the air pressure.
Temperature
• Hot temperatures have low air
pressure Cool temperatures have
high air pressure. (think of the lava
lamp!)
• Places with HIGH (hot) temperatures
have LOW air pressure.
• Places with LOW (cold) temperatures
have HIGH air pressure.
Air Pressure and Weather
• When the air pressure in an
area is HIGH, it is preventing
clouds from entering the
area…therefore, the weather is
usually fair (nice).
• Conversely, when the air
pressure in an area is LOW, it
allows clouds to enter the
Winds
How does wind form?
• When air moves from an
area of high pressure to an
area of low
pressure….winds form!
• Two types of winds:
• 1. Local winds
Local Winds
• Winds that occur over a small area.
• Two types:
• 1. Sea Breeze –
flow of air from the
sea to the land.
• 2. Land Breeze –
flow of air from the
land to the sea.
Global Winds
• Due to temperature variation,
the Earth is heated
unevenly…this causes global
winds!
• Because of the Earth’s rotation,
all winds shift to the right in the
N. Hemisphere and to the left in
the S. Hemisphere. This shift is
Global Wind Systems
• 1. Doldrums – located
at the equator: very calm
• 2. Trade Winds 30°N and S of the
equator: calm…horse
latitudes
• 3. Prevailing
Westerlies - 40°-60°
N. and S…strong
• 4. Polar Easterlies –
approaching 90°N and
Jet Streams
• Discovered in the
1940’s…narrow belt of strong,
high speed, high pressure air.
• Flows approximately 7 miles in
altitude…airplane pilots use the
jet stream to increase speed
and save fuel.
Moisture in the Air
The Water Cycle
HUMIDITY
• During the process of
evaporation, the sun turns
water into a water vapor. This
moisture in the air is called
humidity.
• Winds transport moisture all over th
Relative Humidity
• Relative humidity is the
percentage of moisture the air
holds relative to the amount it
could hold at a particular
temperature!
• To find relative humidity,
meteorologists use a Relative
How to determine relative humidity…
• 1. Determine the dry-bulb thermometer reading.
• 2. Find the difference between the dry-bulb
temperature and the wet-bulb temperature.
• 3. Use the chart to find the relative humidity
expressed as a percentage.
RELATIVE
HUMIDITY
CHART
°C
1
2
3
4
10
88
77
66
55
44
11
89
78
67
56
46
12
89
78
68
58
48
13
89
79
69
59
50
14
90
79
70
60
51
15
90
80
71
61
53
16
90
81
71
63
54
17
90
81
72
64
55
18
91
82
73
65
57
19
91
82
74
65
58
20
91
83
74
66
59
21
91
83
75
67
60
22
92
83
76
68
61
23
92
84
76
69
62
24
92
84
77
69
62
25
92
84
77
70
63
26
92
85
78
71
67
27
92
85
78
71
65
28
93
85
78
72
65
29
93
86
79
72
66
30
93
86
79
73
67
5
Clouds
Clouds form
when
moisture in
the air
condenses
on small
particles of
Three Types of Clouds
• 1. Cumulus –
fluffy and white
with flat bottoms.
Indicate fair
weather
• 2. Stratus – gray
clouds that cover
the entire sky.
• 3. Cirrus – feathery clouds
highest in the sky. Made of
ice crystals because of its
high altitude. Indicate rain
or snow in several hours.
• Anything with the word
“NIMBO” means rain!
4 types of precipitation
• 1. Rain
2. Hail
• 3. Sleet
4. Snow
Weather Instruments
• A RAIN GAUGE is
used to measure
the amount of rain
in a particular area.
•A
THERMOMET
ER
is used to
measure
air
temperature
• A BAROMETER is used to
measure air pressure.
• A WIND VANE is used to
measure wind direction.
• An ANEMOMETER is used
to measure wind speed!
• You measure
RELATIVE
HUMIDITY
with a
psychromete
r!
Weather Patterns
Air Masses
• Changes in the weather are
caused by movements of large
bodies of air. These large bodies
are called air masses.
• There are 4 major types of air
masses:
• 1. Maritime tropical
• 2. Maritime polar
Let’s break down these words…
• Maritime means “relating to the sea”
• Continental means “of the land”
• Tropical means “warm”
• Polar means “cold”
• So….an air mass that is maritime
tropical means that it is over WATER and
HOT!
• Remember…evaporation takes place
over water so it is over water where there
is a lot of moisture or water vapor.
Fronts
• Fronts form where two air
masses meet
• There are 4 types of fronts:
COLD FRONT
WARM FRONT
OCCLUDED FRONT
STATIONARY FRONT
Storms
• 1. Rainstorms and snowstorms
– both develop when two
different fronts collide. It falls
as rain if above 32°F and
snow if 32°F or below.
• 2. Thunderstorms – When a
cold front moves in and meets
a warm front,
• 3. Cyclones and Anticyclones – both are
affected by air pressure. An area of LOW
pressure that contains rising warm air is a
cyclone. An area of HIGH pressure that
contains cold, dry air is called an anticyclone.
• 4. Hurricanes – A powerful cyclone that
forms over TROPICAL OCEANS!
• 5. Tornadoes – a whirling, funnelshaped cloud. Develops in low, heavy
cumulonimbus clouds.
Predicting the Weather
Weather Maps
• Some information included on a
weather map:
1. Cloud cover
2. Air pressure
3. Temperature
4. Wind speed
5. Wind direction
•H Area of high pressure (nice
weather)
•L Area of low pressure (cloudy,
rainy
ISOTHERM AND ISOBAR
• Let’s break down these words:
• ISO means equal or the same
• THERM reminds me of a thermometer
(which measures air temperature)
• So an isotherm means areas with the
same air temperature
• BAR reminds me of a barometer
(which measures air pressure)
• So an isobar means areas with the
Isobar Map (each color
represents areas with the
same air pressure)
Isotherm Map (each line
represents areas with the same
air temperature)
Cloud Seeding (changing the
weather)
• Most effective use so far is
at the airport to reduce fog
for incoming planes.