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Weather
Weather is ….
• The condition of the variables in the
atmosphere at a given time and place.
• Variables – temp, air pressure, wind,
cloud cover, precipitation, etc.
Measuring
Temperature
• 3 different scales
to measure temp.
• Celsius
• Fahrenheit
• Kelvin
ESRT pg 295 (13)
Temp is ….
• Measured using a thermometer (liquid
filled glass tube)
• Modeled on maps or charts by using
isolines (isotherms)
• The atmosphere is heated in many ways:
– Insolation from the Sun
– Conduction
– Condensation
– Coriolis effect
• Heat energy is transferred in our
atmosphere by the process of
convection.
A closer look at CONVECTION:
Transfer of heat energy through
substances which can flow.
A convection cycle
air
Molten rock
5. Rising heated water
moves outward to
replace sinking cooler
water.
4. Cooler more dense
water sinks.
3. Water moves in to
replace rising warm
water
water
2. Lower density
warmer water rises
upward.
Heat
source
1. Heating causes a
decrease in density
Air Pressure
• Air Pressure- Pressure
due to weight of the
overlying atmosphere
pushing down on a given
area.
• Pressure & Density are
directly related
• Density = Pressure
Measuring Air Pressure
Barometers
– Mercury barometer
• Standard reference but
difficult to transport
(inches of mercury)
–Aneroid barometer
•Non-liquid barometer that is
smaller (millibars)
ESRT pg 295 (13)
1013.2 mb = ________
inches
29.92
30.18
1022.0 mb = ________
inches
30.53 inches = ________
1034.0 mb
1009.5 mb
29.81 inches = ________
What Effects Air Pressure?
• As the temp of air increases the
decreases
density & pressure _____________
• As the altitude increases the density
decreases
& pressure _______________
• The greater the amount of water
vapor, the lower the air pressure &
density…. but WHY?
Water has less
mass than other
elements, which
it replaces in
the atmosphere.
Practice Questions
According to the Earth Science
Reference Tables, an air pressure of
30.15 inches of mercury is equal to
1. 1017 mb
2. 1019 mb
3. 1021 mb
4. 1023 mb
A balloon carrying weather instruments is
released at the Earth’s surface & rises through
the troposphere. As the balloon rises, what will
the instruments generally indicate?
1. An increase in both air temp. & air
pressure
2. A decrease in air temp. & an increase in
air pressure
3. An increase in air temp. & a decrease in
air pressure
4. A decrease in both air temp and air
pressure
A temperature of 80°F would be
approximately equal to how many
degrees on the Celsius scale?
1. 27
2. 299
3. 178
4. 34
Layers of our Atmosphere
http://www.youtube.com/watch?v=F
HtvDA0W34I
Where was he?
• Jumped from 128,000 feet, or 24
miles!
Mapping Temperature and
Air Pressure
Why Use Weather Maps?
• Weather maps help us picture what is
going on in the atmosphere.
– Data is collected in multiple locations,
and is displayed in a format that can be
understood easily by people.
• The information is placed on weather maps.
Isolines
• Connect points of equal value on a
map. Ex.: Temperature, Pressure,
Elevation.
Types of Isolines
• Isotherms – connect points of equal
temperature.
• Isobars – connect points of equal air
pressure.
Rules For Drawing Isolines
1. Isolines begin and end at the edges of the
map OR form closed circles.
2. Isolines connect points of equal value.
3. The isoline interval is the difference
between two neighboring isolines.
4. Isolines NEVER cross because the point of
intersection would have two values, and this
cannot happen.
Gradient
• Gradient – Shows how much
something changes over a distance.
• Calculating Gradient:
– Gradient = Change in field value
Distance
Wind
•Horizontal movement of air parallel to earth’s surface
RANDOM FACTS:
Fastest wind struck
Oklahoma City on May 3,
1999.
(SPEED was 318 mph)
Two of the windiest
cities are found in
Massachusetts
10 windiest cities
Avg annual wind speed in
mph
1. Blue Hill, Ma
15.4
2. Dodge City, Kansas
14.0
3. Amarillo, Texas
13.5
4. Rochester, Mn
13.1
5. Casper, Wyoming
12.9
6. Cheyenne, Wy
12.9
7. Great Falls, Montana
12.7
8. Goodland, Kansas
12.6
9. Boston, Ma
12.5
10. Lubbock, Texas
12.4
ANEMOMETER
– Instrument used to measure wind speed
-Measured in miles per hour & knots
•Caused by DIFFERENCES in air pressures
for a specific distance
AIR PRESSURE GRADIENT
CLOSER THE ISOBARS =
GREATER Pressure Gradient & FASTER
Wind Speed
WIND MOVES FROM:
Areas of HIGH pressure to areas of LOW pressure
Coriolis effect (Earth’s rotation) causes
winds to move..
-RIGHT Northern Hemisphere
-LEFT Southern Hemisphere
MYTH OF THE TOILET
One can find both
counterclockwise and
clockwise flowing drains in
both hemispheres. Some
people would like you to believe that the
Coriolis force affects the flow of water
down the drain in sinks, bathtubs, or
toilet bowls. Don’t believe them! The
Coriolis force DOES NOT affect
such small bodies of water
Planetary winds in the Troposphere
Unequal heating of
Earth causes huge
CONVECTION CELLS
around Earth
Rising Moist Air
Sinking Drier Air
HIGH
LOW
Sinking Drier Air
HIGH
ESRT pg. 14
Rising Moist Air
LOW
Sinking Drier
Air
HIGH
LOW
Rising Moist Air
HIGH
Sinking Drier Air
Closer Look
• Bands of easterly moving air at the top of the
troposphere called JET STREAMS
-Blow 200 miles an hour or more
Local Breezes
SEA BREEZE
Air blows from the
sea onto the land
during the day
LAND BREEZE
Air blows from the
land out to sea at
night
Surface Ocean Currents
• Caused by wind blowing over the oceans &
transferring energy to the water
DIRECTION of CURRENTS is affected by:
1) PLANETARY WIND BELTS
2) ROTATION of EARTH
3) BLOCKING BY LANDMASSES
High Pressure System
• AKA - anticyclones
•Highest Pressure in
CENTER
•Winds blow OUT
•Winds move
CLOCKWISE
High and Dry!
Low Pressure System
• AKA - Cyclones
•Lowest Pressure in
CENTER
•Winds blow
TOWARDS the
center
•WINDS move
COUNTERCLOCKWISE
LOUSY DAY!!
Two weather stations are located near each
other. The air pressure at each station is
changing so that the difference between the
pressures is increasing. The wind speed
between these 2 locations will probably
(1) decrease
(2) increase
(3) remain the same
On which side of the low-pressure center
will the wind speed be greatest?
(1) North (2) South (3) East
(4) west
Which location is experiencing a southwest
planetary wind?
(1)
(2)
(3)
(4)
A
B
C
F
Which location is near the center of a lowpressure belt where daily rains, are
common?
(1)
(2)
(3)
(4)
E
B
F
D
Atmospheric Moisture
-Amount of moisture in the air is constantly changing
3 STATES of MATTER:
1) LIQUID
2) SOLID
3) GAS
**Gaseous water in the atmosphere is called
WATER VAPOR**
Water vapor enters the atmosphere by:
EVAPORATION
TRANSPIRATION
LIQUID changes to
GAS
PLANTS release
water vapor
SUBLIMATION
Change of phase from
SOLID to GAS
(NO LIQUID PHASE)
Factors INCREASING Evaporation:
1) MORE ENERGY available
2) INCREASE in SURFACE AREA of the water
3) GREATER WIND SPEED
Factors DECREASING Evaporation:
1) INCREASE in SATURATION of the air
Humidity
ABSOLUTE HUMIDITY
– AMOUNT of water vapor present in the air
MOISTURE CAPACITY
– TOTAL amount of water vapor the air can hold
RELATIVE HUMIDITY
– Ratio between the amount of moisture in the air
with the amount the air can actually hold at that
temperature
Relative Humidity & Temperature
HOT AIR HOLDS MORE MOISTURE THAN
COLD AIR
EXAMPLES:
INCREASES
1) Temperature _______________but
amount of
water vapor remains the SAME, then the Relative
DECREASES
Humidity will _______________.
DECREASES
2) Temperature _________________
but amount
of water vapor remains the SAME, then the
INCREASES
Relative Humidity will __________________.
3) Temperature remains the SAME, but MORE water
vapor is added, then the Relative Humidity will
__________________.
INCREASES
Determining Relative Humidity
-Instrument used to measure called a PSYCHROMETER
Smaller the
difference between
the dry & wet bulb
temperature the
more humid the air
Dew Point
Temperature at which the air becomes
SATURATED with water vapor & the RELATIVE
HUMIDITY is 100%
Air drops TO the dew point
condensation will occur
(CLOUDS FORM)
Determining Dew point on Chart
Dew point = 1oC
Assume a dry-bulb temperature of 10oC
12
& a wet-bulbPg.
temperature
of 6oC. The
difference between these two readings
is 4oC.
Relative
Humidity = 54%
The graph indicates
that as the air
temperature increases,
the relative humidity
1)
2)
3)
4)
Decreases, only
Increases, only
Increases & decreases
Remains the same
Condensation most likely occurred at approximately
(1) 6 am
(2) 9 am (3) 7 pm (4) 10 pm
The dry-bulb temperature is 20oC. The
wet-bulb temperature is 17oC. What is
the dew point?
(1) 12oC
(2) 13oC
(3) 14oC
(4) 15oC
When was the air at ground level SATURATED with
water vapor?
(1) 6 pm MONDAY
(2) 6 am Tuesday
(3) 3 pm TUESDAY
(4) 12 noon Tuesday
The relative humidity was lowest at
(1) 12 midnight
(2) 6 am
(3) 12 noon
(4) 3 pm
Station Model
Open your ESRT to pg 13
Temperature (°F)
Cloud Cover
Barometric
Pressure
Barometric
Trend
Visibility (miles)
Present Weather
Dew Point (°F)
Wind Speed
82
003
5=
65
+34 /
.1
Precipitation
(inches)
Wind Direction
Decoding Barometric Pressure
• If the number given is higher than 500
put a 9 in front and add a decimal in
between the last 2 numbers.
– Example:
• 642  ___________
964.2
997.2
• 972  ___________
• 980  ___________
998.0
• If the number given is lower than 500
put a 10 in front and add a decimal in
between the last 2 numbers.
– Example:
1032.0
• 320  ___________
1024.0
• 240  ___________
1004.0
• 040  ___________
Encoding Barometric Pressure
Example: 1013.7 mb
a. Drop the decimal point = 10137
b. Report the last 3 digits = 137
Practice:
160
1016.0 _____________
984.0  ____________
840
Understanding Barometric Trend
SYMBOLS
+  pressure was HIGHER than 3 hours ago
–  pressure was LOWER than 3 hours ago
/  pressure is rising
\  pressure is falling
-  pressure is steady
Number  decimal point is missing
Example:
32 = 3.2
Practice Question
• Pressure = 230
• Trend = + 34 /
a. ____________________
1023.0
Higher
b. ____________________
3.4 mB
c. ____________________
1023.0 – 3.4 = 1019.6
d. ____________________
Still Rising
e. ____________________
35
8
10
199
+31 /
.03
a. Wind Direction ____________
Northwest
b. Wind Speed
15 knots
____________
35°F
c. Temperature ________________
10°F
d. Dew point Temperature _________
1019.9 mb
e. Barometric Pressure ____________
f. Barometric Trend ______________
3.1 & Rising
g. Cloud Cover _________________
0%
AIR MASS
–Large body of air in the troposphere with
similar characteristics of PRESSURE,
MOISTURE, & TEMPERATURE
• Forms when a
large mass of air
remains
STATIONARY
for a period of
time acquiring
similar
characteristics.
• Temperature:
– High Latitude  _____________
Low Temp
– Low Latitude  ______________
High Temp
• Humidity:
– Land  _____________
Dry Air
Wet Air
– Water  _____________
m = maritime (water, wet)
T = Tropical 
(low latitudes & hot)
c = continental (land, dry)
P = Polar 
(high latitudes & cold)
Tornado Alley
Cold Front
Cold air is
pushing
forward
into
warmer
air.
Cold Front
• Strong storms can occur, such as
thunderstorms.
Warm Front
Warm
air is
pushing
forward
into
colder
air.
Warm Front
• Steady rain can occur leading up to the
warm front.
• High elevation clouds are seen ahead of
the warm front.
Why is precipitation
associated with fronts?
Adiabatic Heating and Cooling
Adiabatic Cooling
When air rises, it
expands, and the
temperature of the
air decreases.
Adiabatic Heating
When air sinks, it
condenses, and the
temperature of the
air increases.
Elevation
• Elevation increases, the air becomes less
dense and expands.
–Less-dense air cannot hold as much HEAT
Elevation
= Temperature
Precipitation at High Elevation
The air reaches its dew point
– Condensation forms clouds
– Precipitation starts to fall
• http://www.phschool.com/atschool/phsciex
p/active_art/weather_fronts/
Cold Front
Cold air is
pushing
forward
into
warmer
air.
Warm Front
Warm
air is
pushing
forward
into
colder
air.
Occluded Front
Warm Air
Warm Air
Stationary Front
Both cold & warm
air are pushing
forward
Practice Questions
A mT airmass would most likely originate over
which type of Earth surface?
A) warm and moist
B) cold and dry
C) cold and moist
D) warm and dry
Which map correctly shows the wind directions
of the high-pressure and low-pressure
systems?
The cold frontal interface is moving faster than the
warm frontal interface. What usually happens to the
warm air that is between the two frontal surfaces?
A) Warm air is forced under both frontal interfaces.
B) Warm air is forced under the cold frontal
interface but over the warm frontal interface.
C) Warm air is forced under the cold frontal
interface but under the warm frontal interface.
D) Warm air is forced over both frontal interfaces.
4. Compared to a maritime tropical airmass, a
maritime polar airmass has
A) lower temperature and less water vapor
B) higher temperature and less water vapor
C) lower temperature and more water vapor
D) higher temperature and more water vapor
5. How does air circulate within a cyclone (low
pressure area) in the Northern Hemisphere?
A) counterclockwise and away from the center of
the cyclone
B) clockwise and away from the center of the
cyclone
C) counterclockwise and toward the center of the
cyclone
D) clockwise and toward the center of the cyclone
• Climate: the overall
view of a region’s
weather conditions
over a long period of
time
Station
Distance
WANTAGH CEDAR
CREEK
5.3 miles
Jan Temp 24 to 37 F
Apr Temp 40 to 55 F
Jul Temp
67 to 81 F
Oct Temp 47 to 62 F
Annual
Precip
42.9 inches
JFK
• The two main factors that
determine climate are
• Temperature
• Precipitation
• Annual Temp Range – difference between
average temp of the hottest month & the
coldest month
• Arid or Dry when… • Humid or Wet when…
– precipitation is
– Precipitation is
less than the
more than the need
need
World Climate Map
Latitude
• Temp varies with
latitude because of
the relationship
between the angle
of intensity &
duration of sunlight
• Low Latitudes
-Sun usually HEIGHEST in sky
– average temp. is always high
• High Latitudes
– Sun usually LOWER in sky
– average temp. is low
Moisture
• Moisture varies
because of
planetary winds
& pressure
belts
Low Pressure –
Humid
Climates
___________
High Pressure –
Dry Climates
___________
**Wet & Dry Belts
are in the ESRT Pg
14 (296)**
Practice Questions
A high air-pressure, dry-climate belt is
located at which Earth latitude?
A) 30°N
C) 0°
B) 15°N
D) 60°N
The planetary wind & moisture belts
indicate that large amounts of rainfall
occur at Earth’s equator because air at
Earth’s surface is
A) Converging & rising
B) Converging & sinking
C) Diverging & rising
D) Diverging & sinking
An area with a high potential for
evapotranspiration has little actual
evapotranspiration and precipitation. The
climate of this area is best described as
A) cold and arid
B) hot and humid
C) cold and humid
D) hot and arid
Which generally has the greatest effect
in determining the climate of an area?
A) Degrees of longitude
B) Extent of vegetation
C) Distance from the equator
D) Month of the year
According to the ESRT, at which of these
latitudes would average annual
precipitation be greatest?
A) 90°S
C) 30°N
B) 90°N
D) 0°
Large Bodies of Water
• Lake, ocean, seas modify climate patterns
•Water takes time to HEAT up & COOL down
because it has a HIGHER SPECIFIC HEAT
MARINE CLIMATE
Cooler Summers &
Warmer Winters
-Small annual
temperature range
CONTINENTAL CLIMATE
Cooler winters & warmer
summers
-Large annual temperature
range
Ocean Currents
• Currents flowing away from the equator carry
WARM water to higher latitudes
•Causes WARMER
Climates & MORE
precipitation
-
•Currents flowing
toward the equator
carry COOL water to
lower latitudes
•COOLER climates with
LESS precipitation
Prevailing Winds
• U.S. located in the prevailing southwesterly
wind belt
•Weather moves from
Southwest to Northeast
CALIFORNIA has
more of marine
climate because
prevailing winds
blowing from the
coast
MONSOONS
Weather changes
caused by the
seasonal shifts of
Prevailing Winds
-Mostly associated
with southeast Asia
causing wet
summers & dry
winters
El Nino
El Nino ANIMATION
-Periods of ocean WARMING along the Pacific coast of
South America
El Nino & La Nina
Which graph
best represents
the yearly
temperature
variation for
location B?
Which location probably has the highest
average yearly temperature?
1) A
2)B
3)C
4)E
Why are temperature variations usually not
as great on Long Island as they are in
central NYS?
1) Central NYS has a higher elevation
2)Central NYS is more heavily wooded
3)Long Island has a more southerly latitude
4)Long Island is surrounded by a large body
of water
According to this diagram, between which 2
latitudes are the prevailing southwesterly winds
located?
2) 30°N and 0°
1) 30°N & 60°N
3) 30°S and 0°
4) 30°S and 60°S
Elevation
• Elevation increases, the air becomes less
dense and expands.
–Less-dense air cannot hold as much HEAT
Elevation
= Temperature
Precipitation at High Elevation
The air reaches its dew point
– Condensation forms clouds
– Precipitation starts to fall
Mount Kilimanjaro
Mountains
There are two sides to a mountain range:
• Windward
– The side that
faces oncoming
winds
– Rain or snow fall
in this side
• Leeward
– The downside of the mountain
– Dry air, sometimes called the rain
shadow
– Often times you will find a desert
located here
Vegetation
• Forests are cut down, deforestation,
RUNOFF
more ____________
occurs
Without trees to absorb solar energy from sun:
-SUN heats the land & atmosphere faster
Cloud Cover
DURING DAY
• LESS CLOUDS the more
heat reaches the Earth
from the sun
AT NIGHT
•LESS CLOUDS the more
heat is released at night
Practice Questions
Which graph best shows the general effect that
differences in elevation above sea level have on
the average annual temperature?
Location G has a cold, humid climate.
Which profile best represents the position
of location G with respect to the
mountains & the prevailing winds?
The map below shows the location of four
cities A, B, C, & D, in the western US where
prevailing winds are from the southwest.
Which city most likely receives the least
amount of average yearly precipitation?
A) A
B) B
C) C
D) D
What is the best explanation for the two
statements below?
* Some mountains located near the Earth's
Equator have snow-covered peaks.
*Icecaps exist at the Earth's poles.
A) Both mountain & polar regions have arid
climates.
B) An increase in snowfall & an increase in
temperature have a similar effect on climate.
C) Mountain & polar regions receive more energy
from the Sun than other regions do.
D) High elevation & high latitude have a similar
effect on climate.
In the diagram of a mountain below, location A & B
have the same elevation.
Compared to the climate at location A the climate
at B will be
A) Warmer & drier
B) Cooler & drier
C) Warmer & wetter
D) Cooler & wetter