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UNIT 5: WEATHER
& CLIMATE

PACKET 6: STATION MODELS, FORECASTING, FRONTS,
SEVERE WEATHER, AIR MASSES
Whoa! Its raining
buckets out there!
P.S. I’m Harley
EARTH SCIENCE
MS. GILL
NOTE PACKET #6
NAME:_____________________ CLASS:____ DATE:______
________
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Vocabulary
Weather
Gradient
Density
Field
Iso-line
Pollution
Isoline map
Size
Time Frequency
Pressure
Cyclic Change
Atmospheric carbon dioxide
Interface
Air masses
Cold front
Warm front
stationary front
Solar energy
Insolation
Atmosphere
absorbed
Ozone
Water vapor
Reflect
radiation
Conduction
Evaporation
Convection
Weather
Seasonal changes
Atmosphere
Hydrosphere
Density differences
Weather patterns
Weather variables
Air temperature
Air pressure
Moisture
Relative humidity
Dew point
Precipitation
Rain
Snow
Hail
Sleet
Wind speed
Wind direction
cloud cover
Instruments
Thermometers
barometer
Psychrometer
Precipitation gauges
Anemometers
Wind vanes
Probability of precipitation
Air pressure gradient
Vertical atmospheric
movement
Radar
Satellite images
Weather maps
Station models
Isobars
Fronts
Atmospheric cross-section
Computer models
Jet stream
Wind
Air masses
Frontal boundaries
Cyclonic system
Tornadoes
Thunderstorms
Hurricanes
Global temperature zones
Planetary wind
Ocean current patterns
Monsoons
Flooding
Severe weather
Calorimeters
Aluminum bars
Heat transfer
Predict
Weather event
Natural disaster
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Weather is the
__________________________________________________________________
It is the result of the interrelationship of the following 4 atmospheric variables:
I. Temperature: measures how much ____________________ the air molecules have
II. Air Pressure: caused by the __________________ of atmosphere pushing down
III. Wind: Horizontal Movement of air caused by ___________________in pressure
IV. Humidity: Moisture content of the atmosphere
In what layer of our atmosphere does our weather occur? ______________________________
What is our atmosphere made of? __________________, _________________, ___________
Use your ESRT to answer the following
questions:
What happens to the temperature of the
atmosphere as altitude increases
through the troposphere?
______________________________
______________________________
2. In what layer of the atmosphere is the
most water vapor found?
____________________
3. What is the exact altitude, in miles, of
the Stratopause?
_______________________
4. What is the pressure at an altitude of
15km? _________________________
5. What is the temperature at an altitude
of 50 miles? __________________
6. What is the temperature at an altitude
of 0 miles? __________________
7. What is the temperature at an altitude
of 30km? ____________________
8. What happens to the temperature of the
atmosphere as altitude increases
through the stratosphere?
______________________________
______________________________
9. How does pressure change with altitude?
______________________________
10. What is the exact altitude, in
kilometers, of the Tropopause? ___________________
1.
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I. Temperature:
Temperature is a measure of how much kinetic energy the air molecules have in a parcel of air, or simply
a mass of air. The average kinetic energy of the particles is dependent on energy transfer. Remember, Earth is
always trying to achieve equilibrium, and distributes energy from areas of high temperature to areas of low
temperature. In other words energy will always flow from the warmer energy source to the cooler energy sink.
The major source of energy for Earth is our Sun. Insolation from our sun heats the ground and bodies of
water covering earth’s surface. In turn, these surfaces reradiate the sun’s energy as infrared radiation that
heats the air. However, there are many factors that contribute to how much of the insolation is actually
absorbed and reradiated by Earth’s surface. This unequal absorption causes unequal heating of our atmosphere.
Once again, since energy always flows from high to low, convection currents form in our atmosphere to try to
distribute the heat energy evenly.
There several properties of earth’s atmosphere and surface that affects the amount of insolation that
is absorbed. The more solar energy that reaches and is absorbed by earth’s surface, the hotter the air above it
will become. Lets look at some of the variables that cause unequal heating of earth’s atmosphere.
Properties of the Atmosphere and Lithosphere that effect Intensity of Insolation
A) Particulate Matter prevents Insolation from reaching earth’s Surface:
Aerosols like water droplets, volcanic dust, ice crystals and pollutants can LOWER the air temperature because
they cause SCATTERING that result in LESS insolation reaching Earth’s surface.
B) Clouds:
During the day clouds scatter insolation and prevent insolation from reaching earth’s surface. Thus it is colder
on a cloudy day. However, at night the water vapor acts as a greenhouse gas and traps the reradiated infrared
heat energy. Thus it is warm and humid on a cloudy night.
C) Surface over which air Exists
Air is warmed by reradiated infrared radiation from the surface over which the air exists. Convection currents
then distribute the warm, less dense air in the atmosphere. Therefore, a dark rough surface will have warmer
air mass above it than a light colored smooth surface.
D) Latitude and Season
Due to earth’s revolution and the tilt of our axis, different latitudes on earth experience variations in
insolation though out the year. In general the tropical latitudes receive the most intense angle of insolation
where as the poles receive less intense insolation.
Convection currents form in our atmosphere due
to this unequal heating.
Warmer air is less dense and therefore will rise,
whereas cold air is more dense and will sink. This
is due to the fact that fluids (gas and liquids) tend
to layer based on density, with densest fluids
beneath less dense fluids. However when cool
dense air sinks, it eventually hits the earth’s
surface. It has nowhere to go except to flow
horizontally across earth’s surface. You
experience this phenomenon when you stand in the
wind. The cool dense air rushes down and across
earth surface to a region where air is rising and
needs to be replaced. You might recall this
concept from our energy unit, this type of energy
transfer is called a convection current.
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I. Air temperature: Total Kinetic energy of air particles
A. Three scales used to measure Temperature:
1. _____________________
2. _____________________
3. ______________________
Ice
Boiling water
Fahrenheit
Celsius
Kelvin
Absolute Zero: (Zero degrees Kelvin)
____________________
NO KINETIC ENERGY! MOLECULES ARE NOT MOVING!
B.. The Affects of Air Temperature:
1.
2.
3.
4.
Which
Which
Which
Which
container has more kinetic energy?__
container has higher air pressure?___
container has greater density?___
container can hold more water?___
Summary:
*Hot air has more kinetic NRG
*Hot air has less pressure
*hot air can hold more water
*hot air is less dense
*hot air rises
You need to know the following weather instruments:
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II. Air Pressure:
Air pressure is the result the weight of atmosphere pushing down on Earth’s Surface. We live on the
bottom of an ocean of air; therefore the pressure is highest at low elevations because there is a tall
column of air molecules above you. As you increase your elevation, less air molecules are above you, so
air pressure decreases and your ear’s pop. Humans have evolved over the last 20 million years to be
strong and accustomed to this pressure. Therefore your body does not notice small changes in air
pressure, nor do you “feel” the weight of the air normally.
Air will either Rise or Sink based on its temperature, this results in
LOW and HIGH Pressure systems to an observer on earth’s surface.
Whenever you watch the weather channel you will often see giant red “L’s” and blue “H’s”
over different parts of the U.S. on a synoptic weather map. This indicates the vertical
movement of air and the weather that results from it.
In a low pressure system, air is rising because it is warm and less dense. (We can model
this using our hand above our head. If you move your hand upward away from the top of your
head, you will not exert pressure on you head.) This rising moist air leads to cloud development
and bad weather!
However in a High pressure system, air is sinking because it is cool and more dense. (This
can also be modeled using your hand. If you lower your hand toward your head, allowing your
hand to “sink” you will exert a high amount of pressure on your head) Sinking air is associated
with good weather and no rain, so give your friend next to you a “HIGH FIVE” for nice weather!
(PUN INTENDED)
This vertical movement of air is best visualized using an atmospheric cross section
like the one below:
Moisture in the Air affects Air pressure too!
Dry air is made up mostly of Nitrogen and Oxygen… theses are heavy gases because they have
many protons. Furthermore, cooler air is dry since the particles are closer together (more dense) and
there isn’t a lot of room for water to fit. These heavy densely pack molecules in dry air exert a lot of
pressure on earth’s surface.
Moist air on the other hand is usually characteristic of less dense warm air. Also water vapor is
made up of hydrogen and oxygen. Hydrogen is a much lighter gas compared to nitrogen and so moist
air in general is lighter than dry air. The light, less dense molecule of moist air does not exert as
much pressure on earth’s surface as dry air does.
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II. Air Pressure: Caused by the weight of the atmosphere pushing down.
A) As Altitude increases, Pressure decreases!
Graph the following relationships:
Pressure
Pressure
Altitude
Air Temperature
A barometer measures: pressure in ___________________________
or millibars.
Standard pressure is _________________or ____________________
(See reference tables page 13)
1040.0 millibars = _____________________ inches of mercury
B) Affects of Water Vapor on Atmospheric Pressure:
Atmospheric Pressure is affected by
_______________________________________________
Water vapor is very _______________________ compared to dry air.
So, when water vapor is added to dry air, the air pressure
____________________
In Summary:
Pressure
Humidity
Cold
Heavier
More Dense
Hot
Lighter
Less Dense
More Pressure
Less Pressure
Holds More Water
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Lows and Highs
A. Portions of the troposphere with low pressure centers are called LOWS or
________________________. Wind direction in a low pressure air mass (in the Northern
Hemisphere) is _______________________________ toward it’s center. Usually associated
with ____________________, ____________________ and _________________ weather.
B. Portions of the troposphere with high pressure centers are called HIGHS or
________________________. Wind direction in a high pressure air mass (in the Northern
Hemisphere) is _______________________________ away from it’s center. Usually associated
with ____________________, ____________________ and _________________ weather.
To summarize: In the diagrams below place curved arrows to indicate the direction the wind is
blowing. Note that the circles are isobars and that this diagram represents an aerial view.
In low pressure winds blow
( in or out )
( clockwise or counter clockwise )
L
In high pressure winds blow
( in or out )
( clockwise or counterclockwise )
Aerial View
H
The diagram below shows a cross-sectional view of how theses air masses move over land
Side View
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III. Humidity:
The amount of water in the air can be measured in different ways. The specific humidity of air
is a measure of how much water is in the air. Warmer air can hold more water than colder air. When
the air reaches its capacity, it is saturated. This capacity doubles for about every 11°C rise in
temperature. The term more often used is relative humidity. This is the measure of how much water
is in the air divided by how much it can hold. The relative humidity reading is given as a percent. The
relative humidity for saturated air is 100 percent. Lets look at the diagrams below to see if you can
figure out why warm air has the ability to hold more water vapor than cold air:
Since the particles in warm air are more spread out, there is more room for water vapor to occupy.
Cold air is more dense on the other hand and is not able to hold as much water vapor.
Temperature effect on the Amount of Water Vapor in the Air:
Temperature is a measure of the kinetic energy of the particles. As the temperature
increases, the motion of the particles in the material increases. As the temperature of a liquid
increases, the speed of the liquid particles increases. As particle speed increases, the particles move
farther and farther apart until finally they separate and are in a gas state. So an increase in
temperature increases the evaporation rate of a liquid. The more evaporation that takes place, the
more moisture there will be in the air.
Moisture in the Air affects Air pressure too!
Dry air is made up mostly of Nitrogen and Oxygen… theses are heavy gases because they have
many protons. Furthermore, cooler air is dry since the particles are closer together (more dense) and
there isn’t a lot of room for water to fit. These densely pack molecules in dry air exert a lot of
pressure on earth’s surface because they are heavier.
Moist air on the other hand is usually characteristic of less dense warm air. Also water vapor is made
up of hydrogen and oxygen. Hydrogen is a much lighter gas compared to nitrogen and so moist air in
general is lighter than dry air. The light, less dense molecule of moist air does not exert as much
pressure on earth’s surface as dry air does.
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Dew Point and Relative Humidity!
Dew Point Temperature: The temperature at which the air is holding the ____________ amount of water.
The air is _____________
Relative Humidity: The ratio of the amount of water vapor in the air, to the maximum amount it can hold. It
is usually expressed as a __________. As the temperature increases, the maximum absolute humidity
_____________ but the relative humidity will decrease
The dew point and relative humidity are determined by using an instrument called a
___________________
The psychrometer has two thermometers, a dry bulb and a wet bulb. The psychometer is whirled in the air
so that evaporation will occur. The lower the moisture content of the air, the ________ evaporation will
occur from the wet bulb and the wet bulb temperature will be _________
1. The diagram below shows the temperature readings on a weather instrument.
Based on these readings, the relative humidity of the air is closest to
1) 32%
2) 8%
3) 11%
4) 60%
2. What is the dewpoint if the relative humidity is 100% and the air temperature is 20ºC?
1) 16°C
2) 18°C
3) 20°C
4) 21°C
3. What is the dewpoint when the dry-bulb temperature is 24°C and the wet-bulb temperature is 21°C?
1) 20°C
2) 6°C
3) 24°C
4) 14°C
4. On a cold winter day, the air temperature is 2°C and the wet-bulb temperature is –1°C. What is the relative
humidity at this location?
1) 37%
2) 6%
3) 83%
4) 51%
5. Which statement best explains why an increase in the relative humidity of a parcel of air generally increases
the chance of precipitation?
1) The amount of moisture in the air is greater, making the air heavier.
2) The specific heat of the moist air is greater than the drier air, releasing energy.
3) The air temperature is closer to the dewpoint, making cloud formation more likely.
4) The dewpoint is farther from the condensation point, causing rain.
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III: The Formation of Clouds
A.
Cloud: a large group of water droplets suspended in _________.
B. Steps involved in cloud formation:
___________________________________
__________________________________
___________________________________
____________________(gas to liquid phase change in which water vapor changes to droplets)
1.
Describe the mass of air that would lead to cloud formation in terms of temperature, humidity, density.
_______________________, ________________________, ____________________________
2.
The air will __________________ because of ____________________ density.
3.
Describe what the air does as it rises:
_______________________, ________________________, ________________________
4.
Clouds will form if this rising moist air:
a. cools to the ___________________ temperature and there by change phase can occur.
b. has ___________________________available, such as dust, pollutants, etc.
C. Basic Cloud Types:
1. Cirrus: high and feathery (____________
weather)
2. Cumulus: White and puffy
(_____________ weather)
3. Stratus: covers the sky like a blanket
(_____________________________)
4. Nimbus: Low Clouds
Alto: Middle Clouds
Cirrus: High Clouds
Steps involved in cloud formation:
-WARM MOIST AIR RISES due to LOW DENSITY
-This parcel of air COOLS DUE TO EXPANSION (adiabatic cooling process)
-Water vapor CONDENSES when the DEW POINT Temperature is REACHED
-Water droplets coalesce AND EVENTUALLY PRECIPITATE
Rising
1.
2.
3.
Air Results in clouds!!!!! What are some situations that will cause air to rise...
When to diffent air masses meet (frontal boundaries)
Windward side of a mountain
Above hot surfacese that cause the air to get less dense and rise!
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D. Effects of a Mountain Range: __________________________________
Label the diagram.
1. The side of the mountain with the moist prevailing winds is called the
_______________________
Summary:
HOT MOIST AIR RISES, EXPANDS, _______ AND THEN CONDENSES! if air is forced to
expand, the air will cool down because molecules will not hit into each other as often and energy
will dissipate (decrease due to spreading out in all directions) and therefore the energy will
disperse into the atmosphere. Once the hot moist air begins to cool, it the water vapor condenses
because cold air can not ________ as much water as hot air, thus producing rain.
2. The air descends to the other side of the mountain which is called the
_______________________
Summary:
DRY AIR SINKS COMPRESSES AND THEN _______. Since all the moisture has been “wrung”
out on the windward side the air on the leeward side is dry. Due to gravity and weight this dry air
sinks, the force of this sinking air causes air pressure to increase. Since the close air molecules
hit into each other more often, more friction between molecules takes place, therefore the air
temperature begins to increase again or ____________.
E. Precipitation:
1. Describe what causes precipitation. Precipitation forms around ___________ particles
(pollutants) droplets combine (____________________) and therefore become heavier and
eventually ___________.
2. Explain why precipitation cleans the atmosphere.
As precipitation forms around dust or pollutants…. They are removed from the atmosphere as
precipitation falls.
3. When the dew point temperature and air temperature approach each other what happens to the
chance of precipitation and why?
The chance of precipitation _____________ because the air is more __________________.
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IV. Wind:
Wind is the horizontal movement of air caused by differences in pressure between two
adjacent air masses. Wind refers to any flow of air relative to the earth's surface in a horizontal
direction. In meteorology winds are named for the direction that they blow from. This is because
although we might have an idea which way the wind will blow, we never know for sure because it has
not happen yet and could change direction at any time.
There are two types of winds: local and planetary. Breezes that blow back and forth from a
body of water to land areas— land and sea breezes—are examples of local wind. Planetary Winds are
driven by much larger pressure systems that exist above the tropics and the poles. These great wind
belts comprise the earth's atmospheric circulation as a whole.
The ultimate cause of Earth's winds is solar energy. When sunlight strikes Earth's surface, it
heats that surfaces differently depending on their specific heat, texture and color. Newly turned
soil, for example, absorbs more heat than does snow. This uneven heating of Earth's surface, in turn,
causes differences in air pressure at various locations. On a weather map, these pressure differences
can be found by locating isobars, lines that connect points of equal pressure. The pressure at two
points on two different isobars will be different. A pressure gradient is said to exist between these
two points. It is this pressure gradient that provides the force that drives air from one point to the
other, causing winds to always blow from high pressure to low pressure. The magnitude of the winds
blowing between any two points is determined by the pressure gradient between those two points.
The closer the isobars the steeper the gradient and the faster the wind.
In many locations, wind patterns exist that are due to local topography and or water masses.
In most cases, unusual topographic or geographic features are responsible for influencing local wind
direction. Land and sea breezes are typical of such winds. Because water heats up and cools down
more slowly than does dry land, the air along a shoreline is alternately warmer over the water and
cooler over the land. These differences account for the fact that winds tend to blow offshore during
the evening and on-shore during the day.
Convection Currents form in our Atmosphere
due to this Unequal heating.
Warmer air is less dense and therefore will rise,
whereas cold air is more dense and will sink. This
is due to the fact that fluids (gas and liquids) tend
to layer based on density, with densest fluids
beneath less dense fluids. However when cool
dense air sinks, it eventually hits the earth’s
surface. It has nowhere to go except to flow
horizontally across earth’s surface. You
experience this phenomenon when you stand in the
wind. The cool dense air rushes down and across
earth surface to a region where air is rising and
needs to be replaced. You might recall this
concept from our energy unit, this type of energy
transfer is called a convection current.
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III. Wind: the horizontal movement of air due to differences in air pressure.
A) Winds are described by the direction they ____________________________.
B) Winds distribute energy. They blow from ______________ pressure to ___________ pressure.
C) Fastest winds occur where the isobars are _______________________________________.
Wind!
There are two types of winds, regional and
local. Regional winds extend over a large area
such as several states of the United States.
These are called planetary wind belts and are
huge global systems. Local winds are those that
extend only for a few miles before they die
out.
-Wind blows from HIGH PRESSURE TO LOW
PRESSURE AREAS.
- a difference in air pressure between to places
is called a pressure gradient.
- A STEEP pressure gradient means that
pressure changes quickly, isobars are close
together, and wind speeds are high.
-A gentle pressure gradient means that
pressure changes slowly, isobars are widely
spaced, and wind speeds are low.
The Coriolis Effect:
1) Winds move from high to low pressure but they do NOT move in straight lines
2) The coriolis effect caused by Earth’s rotation, causes winds to be deflected and curve to right in the
northern hemisphere and the left in the southern hemisphere.
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C) The Earth is always trying to achieve ____________________________.
Energy is constantly being re-distributed flowing from ________________ to ______________
How can we decrease pressure without changing our elevation?
Increase _______________ and Increase __________________
Low pressure = Warmer and Wet!!!
High Pressure = Cooler and Dry!!!
Poles
Equator
Temperature
Pressure
Density
Humidity
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V. Convection Cells and Prevailing Winds
1) The sun heats the Earth UNEVENLY because the angle of INSOLATION is great near the equator than
at the poles. This creates a TEMPERATURE GRADIENT.
2) Warm air rises because it is less dense, while colder, more dense air sinks. This causes CYCLIC currents
in the troposphere called convection cells.
3) Around the Earth, there are several alternating
bands of dry, high pressure air, and humid lower
pressure air. Between these bands are the prevailing
wind belts. PREVAILING WIND BELTS refer to the
common wind direction and speed at a given location
and time of year. In New York State, winds blow from
the west and southwest more than from any other
direction. These winds are called the prevailing westerlies,
or southwest winds. Look at the surface winds shown
in diagram to the right. Winds are named for the direction
from which they blow.
4) Look at the two diagrams below. Remember, if the Earth did not rotate, patterns or convection would be
simple. Air would descend in high pressure regions and blow directly toward low pressure centers. All
winds would be north and south winds. However, the rotation of the Earth causes the wind pattern to be
more complex. On a small scale, the winds blow straight but as they cover larger distances, the planet
moves underneath them, causing them appear to be deflected. This causes east and west winds. Rotation
also causes the formation of six smaller convection cells in the upper atmosphere. Regional weather
systems (highs and lows) complicate the matter even more! Winds can come from any direction
depending on changes in the pressure gradient.
*** If the Earth didn’t rotate, cold air
would form over the poles and flow along
the surface toward the Equator. Air would
then warm at the equator and flow back to
the poles. This would create two giant
convections cells over the earth.
*** However due to the Earth’s
rotation the two convection cells break
into six! See page 14 in ESRT
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Planetary Wind Belts:
Planetary Wind Pattern would be simple if the Earth Didn’t Rotate!
Cold air would _______________ at the poles and flow along the
surface of the Earth toward the ___________________.
Air would then warm at the equator and ________________
(due to ________________ density)) and flow back to the _________________
This would create two great _______________________cells over the Earth
Intended
Actual due to Coriolis
(rotation)
_________________ Effect causes the winds to be deflected to the _____________ in the Northern
Hemisphere and to the _____________ in the Southern Hemisphere. This causes the two convection cells to
break into __________ convection cells. See Reference Tables page 14. Label converging and diverging zones
Use your Reference Table page 14 to describe the wind direction for the following latitudes:
1) 42  N
__________________
2) 23 ½  N __________________
3) 23 ½  S ____________________
4) 70  N
__________________
5) Which planetary wind belt is New York State located? _______________________
6) The Coriolis effect causes winds to curve to the ____________ in the N. Hemisphere.
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Global Wind Patterns:
Global air circulation is influenced by:
-Rising hot air and sinking cold air
-Earth’s rotation, through the Coriolis effect.
-The result of these influences is the…
Three Cell Circulation Model:
-Each hemisphere has 3 zones, or cells, of circulation
-The boundaries are latitudes of 0º, 30º, 60º and 90º
-Patterns are due to alternating bands of H and L pressure.
-Wind patterns are different in each cell and are called…
Prevailing Winds: (Highlight the words naming these winds in YELLOW)
-The term prevailing winds belts refers to the general direction of wind in each cell.
-Winds are named for the direction from which they come.
-Prevailing winds flow from high pressure bands to low pressure bands, and are deflected by the Coriolis effect.
Zones of Convergence (Highlight these in BLUE)
Low pressure bands are called zones of convergence because air flows toward them.
Air is hot and humid and there is little or no wind.
Historically called the doldrums, because sailing ships could be stranded for days.
Zones of Divergence (Highlight these in PINK)
High pressure bands are called zones f divergence, because air flows away from them.
Cooler, dry air & many deserts found in these zones.
Historically called the horse latitudes.
Trade Winds are the same as Strong Prevailing Winds! (Highlight these in GREEN)
The Trade Winds are a zone of steady, strong wind, between the doldrums and the horse latitudes.
They are named trade winds because sailing ships would use them as trade routes.
Jet Streams: (Highlight these in ORANGE)
Jet streams are narrow bands of fast moving, high-altitude wind which separates the cold polar air from the
warmer air to the south. Jet stream blow from the West to the East and circle the planet at about 200 mph.
Airlines have to think about these winds when planning their flight paths. You can cut about one half hour off
your travel time if you fly from west to east with the jet stream. You can plan to lose time if you hit one going
the other way from east to west. Jet streams wander and can give rise to weather systems and steer their
movement.
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Local Wind:
Caused by the unequal heating of land and water. This creates density difference!
Coastal Breezes:
When large areas of land an water are adjacent, temperature differences can create winds that
easily observed. By the coast, wind direction can reverse on a daily cycle due to the difference in
specific heats between the land and the water
SEA BREEZE:
On a sunny day, land heats up quicker than water because land has a lower specific heat. Radiation and
conduction from the lands surface heat the air over the land. This heated air expands and becomes
less dense causing it to rise. The result is a breeze that comes from the water to replace the rising
air over the land. Sea breezes are light winds that blow from the water to the land. The breeze will
continue until the land cools in the evening.
LAND BREEZE:
During the night, land cools off quicker than water because land has a lower specific heat. When the
land cools, the air above the land also cools. The air over the water is now warmer than the air over
the land, so the air above the water begins to rise. This causes the wind to change direction, blowing
from the land to the water.
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Monsoons
Monsoons are seasonal changes in the direction of the prevailing winds. They are similar to land and sea breezes
but last for months and move over greater distances. Rainfall in India depends on these seasonal changes.
During the winter, high pressure air over Asia brings dry wind to India, making rain scarce. In the summer,
warm, low pressure air over Asia draws in moist wind from the Indian Ocean bringing rain to India.
Wind Influence on Ocean Currents:
Ocean Currents:
Most interactions between the oceans and the atmosphere are not understood. It is known, however, that
ocean currents are caused by the wind. Winds blow over the ocean, causing surface water to drift along
with them. Moving water piles up, creating pressure gradients within the water. These pressure gradients
produce currents that transfer heat from the equator to the poles. As surface water drifts away with the
wind, cold nutrient rich water from below rises in a process called upwelling. This also is an example of heat
transfer. The oceans have a huge capacity for storing heat energy. As they slowly warm, they also slow the
rate at which the atmosphere warms.
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VI. How air masses and fronts influence the weather:
An Air Mass: is a large body of air (in the troposphere) with similar reading (amounts) of
_____________________, ______________________and ________________________
Where Air Masses Come From:
A. Regions where air masses come from are called ____________________
____________________
B. List the characteristics that an air mass picks up from its place of origin:
1. ______________________ 2. __________________________
C. If the air mass forms at a high latitude (nearer the poles), it will have a____________
temperature.
D. If the air mass forms at a low latitude ( nearer the equator), it will have a ___________
temperature
E. If the air mass originates over water it will be ___________________
F. If the air mass originates over land it will be ____________________
Using page 13 in your E.S. reference tables complete the chart below
Symbol
Origin ( where it formed)
Describe the air mass
continental
maritime
tropical
polar
arctic
Air Mass Track: the _______________ an air mass takes as it travels. In general, air masses and
weather systems move toward the ___________ over the U.S. because the U.S. is located in the
__________________ wind belt.
21
Air Masses:
The map below shows the source regions for air masses that affect North America. The gray area is the North
American continent. The white areas are oceans and other bodies of water. Use the Air Mass symbols key on
page 13 of your ESRT to properly name each of the numbered air masses. Your answers must be CASE
SENSITIVE (use the proper upper and lower case letters)!
Describe the temperature and moisture characteristics for each of the air masses numbered in the diagram (#1
is done for you):
1. cold and moist
2.
3.
4.
22
VII. Fronts: the boundaries between two air-masses
-Usually ___________________
-Often produce _____________________________________________________________
Front Symbols (draw front symbols on lines provided)
The Half circles and the triangles point in the direction of the air masses and front are moving.
___________ 1. A Cold Front: is the interface
between an advancing (moving forward) cold air
mass and stationary slow moving warmer air.
The cold air pushes the warmer air up
producing cumulous clouds and short but
violent thunderstorms. During this abrupt
weather change winds shift from southerly to
northerly. Note the steep slope of the
interface.
___________ 2. A Warm Front:
the interface between an advancing warm air
mass and a retreating mass of
________________________ air. When this
warm air meets and rises over the cold air on
the ground, it causes extended periods of
precipitation. Note the long gentle slope of
the interface.
___________ 3. An Occluded Front:
occurs when a faster moving cold front
overtakes a slower moving warm front and
completely lifts the warmer air off the
ground.
___________ 4. A Stationary Front: occurs
when a warm air-mass and a cold-mass are side by side with neither air mass moving. Weather is
similar to that of a warm front. Note gentle interface slope
*Note: Generally, at fronts between air masses that have different temperatures, Warm air will
________. This creates unstable weather conditions, and produces much of the ____________
that falls on the continental United States.
23
Mid-latitude Cyclones
- Begins when cold air pushes down from the north, changing a stationary front into a pair of warm &
cold fronts moving around a low pressure center.
As the low moves eastward, the cold front overtakes the slower-moving warm front, producing an
occluded front.
- In general these low pressure systems move toward the NORTHEAST in the United States
A to C 12 –24 hours
D can last for 3 – 4
days
-
Cyclones are “driven” by heat energy released by condensation, causing the low pressure to become
even lower, thereby strengthening the winds.
In summer, cyclones move about 800km a day, while in winter they move about 1,100 km a day. A midlatitude cyclone may cover as much as one-half of the entire continental United States at one time.
Sequence of events if you were to experience the passing or a mid-latutide cyclone:
1. Warm front would approach and bring a long period of light precipitation.
2. Then you would have a period of clearing and warm humid weather
3. The cold front would arrive with brief heavy showers, followed by clearing and cooling
Sequence of events if you were to experience the passing or a mid-latutide cyclone:
City 1
-Temperature- decrease
-Pressure- increase
-Precipitation- brief,
heavy, thunderstorms.
City 2
-Temperature- warm, steady
-Pressure- steady
-Precipitation- none, but
humid
1
2
3
City 3
-Temperature- increase
-Pressure- decrease
-Precipitation- light, steady,
long lasting rain
24
VIII. Station Models & Synoptic Weather Maps
Atmospheric variables are collected from thousands of weather stations around the world four times each day.
1. Station Model
Provides a summary of the current atmospheric conditions in an area.
The Barometric Pressure on a Station Map is in code… The number 9 or 10 has been omitted from the
front. Rule for converting the code into millibars:
1. 887 = _____
if the first digit is 5 or greater add ________ and place a decimal point before
the last digit.
2. 165 = _____
if the first digit is less than 5 add ________ and place a decimal point before
the last digit.
Change the following to abbreviated form:
(ENCODE to place on station model)
1028 ____________
Change from abbreviated form:
(Decode to read off station model)
999 ____________
370 ____________
998.1 ____________
Construct the following Station Model:
Cloud cover: 50 %
Air temp = 20°C
Air pressure = 996 mb
Dew point temperature = 18 °C
Wind speed 25 knots
Wind direction SW
Add Rain and A steady 1.9mb rise in
the past 3 hours, still rising.
Construct the following Station Model:
75% clouds
winds from the N.W.
wind speed 35 knots
air temperature 28F, dew point temp. 20F
visibility 5 miles
barometric pressure 1032.5
barometric trend -1.1 and still falling
present weather is snow
Read the station model below:
78
985
77
Wind Speed:____ Direction: ___
Temperature:___ C ___ F __ K
Dew Point: ___ C ____ F
Cloud Cover:____
Pressure: ___ mb ___ inches
Current Weather: _________
25
IX. Synoptic Weather Maps:
Did you know that "Synoptic" comes
from the Greek meaning "at the
same time". So a Synoptic weather
map allows us to view many weather
variables that are occurring
simultaneously
A Synoptic Weather Map is an extremely useful tool used by meteorologists to predict the weather.
These maps analyze large-scale weather systems, particularly high- and low-pressure systems and
hurricanes. The word “Synoptic” comes from the Greek meaning “at the same time.” Therefore a synoptic
weather map summarizes several weather variables that are occurring simultaneously (at one particular
time).
Weather variables that can be gathered using a synoptic weather map include:
- Likelihood of precipitation due to the presence of high and low pressure systems.
- Wind direction and velocity using isobars and pressure gradient
- Local weather and cloud cover indicated by station models
- Air mass tracks and the movement of frontal boundaries associated with mid-latitude cyclones.
The primary reason that our society invests so much money and time into Meteorology is so that people
can prepare for rain or severe weather! Don’t you want to know if you should plan a nice beach trip or if
you should stay in and read a book? So let’s first look at the process the causes precipitation to occur.
Moral of the story: in order for precipitation to occur there must be upward vertical movement of moist air!
Lows Pressure Systems and Fronts on a Synoptic Weather Map indicate this vertical movement of air.
26
Large Scale Weather Systems: Low and High Pressure Systems
Whenever you watch the weather channel you will often see giant red “L’s” and blue “H’s” over
different parts of the U.S. on a synoptic weather map. This indicates the vertical movement of
air and the weather that results from it.
In a low pressure system, air is rising. We can model this using our hand above our head. If you
move your hand upward away from the top of your head, you will not exert pressure. Remember
rising moist air leads to cloud development and bad weather!
However in a High pressure system, air is sinking. This can also be modeled
using your hand. If you lower your hand toward your head, allowing your hand
to “sink” you will exert a high amount of pressure. Sinking air is associated
with good weather (no precipitation) so give your friend next to you a
“HIGH FIVE” for nice weather! (PUN INTENDED)
This vertical movement of air is best visualized using a atmospheric cross section
like the one below:
Highs and Lows on a Synoptic Weather Map:
When examining a synoptic weather map… we are
viewing earth from an aerial view, as if in a plane
looking down on Earth. The surface winds will
always flow from High Pressure to Low Pressure.
This makes sense since sinking air in a high
pressure system will hit the ground and have no
choice but to move horizontally along the surface
toward a low pressure system, where it can
replace rising air. This cycle of air movement is
known as a convection current and is due to
density differences.
Surface winds move toward lows and away
from highs. The greater pressure gradient
the faster the winds will blow. Therefore,
closely spaced isobars indicate fast winds.
27
Application Questions:
In summary the presence of Low pressure systems and High pressure systems on a Synoptic Weather map
enable a meteorologist to predict the probable chance of precipitation on a large scale map.
A. Portions of the troposphere with low
pressure centers are called LOWS or
CYCLONES. Wind direction in a low pressure air
mass (in the Northern Hemisphere) is
COUNTERCLOCKWISE AND toward it’s center.
Lows are usually associated with RAINY
weather (Low and Lousy). Draw three arrows to
indicate the surface wind direction.
B. Portions of the troposphere with high pressure
centers are called HIGHS Or ANTICYCLONES.
Wind direction in a high pressure air mass (in the
Northern Hemisphere) is CLOCKWISE away from
it’s center. Usually associated with FAIR weather
(High and Dry! High Five). Draw three arrows to
indicate the surface wind direction.
1012
L
1016
984
1020
H
988
992
Directions: Draw the following onto the Synoptic Weather Map on the next page and answer the questions.

Label the cold front, the warm front and the occluded front (USE Your ESRT). Remember the combination
of these fronts surrounding a Low is called a Mid-Latitude Cyclone.

Find and label the mT air mass associated with this Mid- Latitude Cyclone.
Is there a high probability that it is raining here? _____
Describe the temperature and humidity of this mT air mass. ________________ & ______________

Place a red “x” over the area experiencing the greatest wind speeds. Site the evidence shown on the map
that enabled you to determine this location:________________________________________________

Draw a green arrow to indicate the wind direction between the High and Low on the Map.
Name this wind: ____________________

With a blue pencil, shade the area on the map that is most likely experience precipitation.
Bonus Question:
In what compass direction will the center of this Mid- Latitude Cyclone most likely move if it follows a normal
storm track. (Hint use the planetary wind diagram on page 14 in your Reference table)
28
29
X. Storms and Severe Weather
A storm is violent episode of heavy precipitation, strong wind, lightning and the danger of flash floods. Most
storms are associated with low-pressure systems, rising warm air, clouds and precipitation.
Types of storms include:
Mid-latitude or cyclonic Storms: Movement of air masses along the polar front can result in the formation of
Mid-latitude cyclones with LOW pressure.
The counter-clockwise rotation of the air is the result of the earth’s rotation,
Which is known as the ___________________________ effect.
Hurricanes: In late summer and early fall LOW pressure centers form over warm tropical ocean water. Winds
can exceed 74 miles per hour. Hurricanes have high winds, high waves, flooding from rain and storm surges of
ocean water along coastlines. If you are in the path of a hurricane you should have food, water and all necessary
supplies and stay indoors. If you live in a flood prone area you should go to an emergency shelter. Board up
windows. Bring in outdoor objects that could blow away. Make sure you know which county or parish you live in.
Know where all the evacuation routes are.
Thunderstorms: Usually form along a cold front producing heavy rainstorms accompanied by thunder and
lightning. Thunderstorms may have strong wind, hail, deadly lightning and produce flash flooding. People in
the path of a thunderstorm should seed shelter indoors, close all windows stay off the phone, turn off
appliances and stay away from flood areas. Stay away from trees if there is no shelter around you.
Tornadoes: rapidly rotating, extremely LOW pressure funnel that hangs down from thunderstorm clouds. They
form when very cold air meets very warm air. Tornadoes are most common in the Midwest where cold, dry air
from Canada meets warm, moist air from the Gulf of Mexico. The tornadoes may stay on the ground for a few
minutes or a few hours. The path of the Tornado is unpredictable. The greatest danger to humans from a
tornado is flying debris picked up by extremely strong winds. People in the path of a tornado should seek low
shelter immediately or go into or under a sturdy structure. Go to a basement. If you do not have a basement, go
to an interior room without windows on the lowest floor such as a bathroom or closet. If you can, get under a
sturdy piece of furniture, like a table. Have a disaster plan. Make sure everyone knows where to go in case a
tornado threatens. Prepare a disaster supplies kit.
Blizzards: associated with heavy snow and winds. Drifting snow can stop transportation. An ice storm can disrupt
electric and phone services. Ice storms can occur suddenly as rainfall begins to freeze. There is a danger of
frostbite and hypothermia. People should stay indoors, not drive, stay warm and have food, water and medical
supplies available.
Emergency Preparedness for Storms:
Describe 4 ways you can prepare for a storm.
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
30
Hurricanes
A hurricane is a huge storm! It can be up to 600
miles across and have strong winds spiraling inward and
upward at speeds of 75 to 200 mph. Each hurricane
usually lasts for over a week, moving 10-20 miles per
hour over the open ocean. Hurricanes gather heat and
energy through contact with warm ocean waters.
Evaporation from the seawater increases their power.
Hurricanes rotate in a counter-clockwise direction
around an "eye." The center of the storm or "eye" is the
calmest part. It has only light winds and fair weather.
When they come onto land, the heavy rain, strong winds
and large waves can damage buildings, trees and cars.
Hurricanes only form over really warm ocean
water of 80°F or warmer. The atmosphere (the air) must
cool off very quickly the higher you go. Also, the wind
must be blowing in the same direction and at the same
speed to force air upward from the ocean surface.
Winds flow outward above the storm allowing the air
below to rise. Hurricanes typically form between 5 to 15
degrees latitude north and south of the equator. The
north easterly prevailing winds bring these hurricanes
westward from the ocean onto the land. The Coriolis
Force is needed to create the spin in the hurricane and
it becomes too weak near the equator, so hurricanes can
never form there.
Tornadoes
Although tornadoes occur in many parts of the world, these
destructive forces of nature are found most frequently in the
United States. They most often occur to east of the Rocky
Mountains during the spring and summer months. In an average
year, 800 tornadoes are reported nationwide, resulting in 80
deaths and over 1,500 injuries. A tornado is defined as a
violently rotating column of air extending from a thunderstorm
to the ground. The most violent tornadoes are capable of
tremendous destruction with wind speeds of 250 mph or more.
Damage paths can be in excess of one mile wide and 50 miles
long. Once a tornado in Broken Bow, Oklahoma, carried a motel
sign 30 miles and dropped it in Arkansas!
Climate:
They are often referred to as a twister or a cyclone, although
the word cyclone is used in meteorology in a wider sense, to name
any closed low pressure circulation.
Thunderstorms develop in warm, moist air in advance of
eastward-moving cold fronts. These thunderstorms often
produce large hail, strong winds, and tornadoes. Tornadoes in the
winter and early spring are often associated with strong, frontal
systems that form in the Central States and move east.
Occasionally, large outbreaks of tornadoes occur with this type
of weather pattern. Several states may be affected by
numerous severe thunderstorms and tornadoes.
31
XI. CLIMATE: Average long term condition of the atmosphere
I. Latitude & Temperature
Locations at low latitudes have HIGH average temperatures
Locations at high latitudes have LOW average temperatures
II. Latitude & Moisture
Where there is low pressure, near the EQAUTROR and at mid-latitudes (60°N & 60S °)…
Air rises, expands, cools and CONDENSES… which leads to PRECIPITATION.
This results in a HUMID climate. At high pressure belts, (near 30°N & 30S °), the air SINKS and
temperatures RISE…
This results in an ARID (dry) climate.
III. Latitudinal Climate Patterns:
The combined effect of temperature and moisture results in a distribution of 4 major climate types
around the world.
These Climate Types are:
a) HUMID >1.2
b) SUBHUMID .8-1.2
c) SEMIARID 0.4-0.8
d) ARID <0.4
Climate zones are based on the ratio between :
PRECIPITATION (P ) and POTENTIAL EVAPOTRANSPIRATION (EP)
Potential evapotranspiration depends on temperature (INSOLATION)
IV. Effect of Large Bodies of Water on Climate:
Large bodies of water modify (change) the climate of an area because of the SLOW heating up and
cooling off of the water.
Summary: (for the same latitude)
-MARINE CLIMATES: have COOLER summers and WARMER winters and a SMALLER range of
annual temperatures.
-CONTINENTAL CLIMATES: have HOTTER summers and COLDER winters and a LARGER range
of annual temperatures.
V. Effect of Large Land Masses on Climate:
Because land heats up and cools off faster than water, temperatures over a CONTINENT (in
mid-latitudes) are WARMER than the oceans in the summer and COLDER in winter.
VI. Storm Tracks & Climate:
In the mid-latitudes (including the continental U.S.) temperatures & moisture are affected by a
succession of low pressure (storm) systems. Generally, these storm centers follow a WEST to
EAST path across the Continental U.S.
32
VII. Ocean Currents & Climate: SEE Reference Table!!!
Coastal climates are modified by ocean currents, for example, a cold ocean current will cause a coastal
area to have COLDER temperatures, and LESS precipitation.
Currents flowing away from the equator carry WARMER water to higher latitudes. Currents flowing
toward the equator carry COLDER water to lower latitudes.
VIII. Elevation & Climate:
The higher the altitude ( at any given latitude), the COLDER it is.
Questions:
1. Why do areas at higher altitudes have less precipitation than lower
altitudes?_________________________________
2. What is the climate type of an area with an annual precipitation of 1089 mm. of water and a potential
evapotranspiration rate of 865 mm. of water?
3. What factors affect the potential evapotranspiration rate of an area?
___________________________________________________________________________________
_______________________________________________________________________________
__________________________________________________________________
4. Which side of a mountain has a more humid climate?
___________________________________________________________________________________
_______________________________________________________________________________
__________________________________________________________________
5. List the factors which effect the climate :
_______________________________________________________________________________
_______________________________________________________________________________
______________________________________________________________________
Use your Reference Table page 14 to describe the wind direction for the following latitudes:
6. 42  N
__________________
7. 23 ½  N __________________
8. 23 ½  S ____________________
9. 70  N
__________________
10. Which planetary wind belt is New York State located? _______________________
11. The Coriolis effect causes winds to curve to the ____________ in the N. Hemisphere.
12. The Coriolis effect causes winds to curve to the ____________ in the S. Hemisphere.
33
La Nina refers to the normal Oceanic
Circulation of the Pacific Ocean:
Cold water comes up from the depths of
Antarctica and travels up beside Peru. It brings
nutrients up to the surface and the fishing is
good. The sinking high pressure zone above the
water pushes down onto the cooler currents
emerging from below. This forces the water
and the air to the west, since the surface of
the ocean is joined to the bottom of the air.
The water is an easterly current going to the
west pushed along by the easterly winds.
Easterly winds bring moisture from the sea and
by the time they arrive on the Australian coast
they are rain-laden.
El Nino & La Nina:
El Nino:
El Nino is a regularly occurring climatic feature
of our planet. Every two to five years, El Nino
reappears and lasts for several months or even
a few years. El Nino takes place when warmer
than usual sea water exists off the coast of
South America. This causes the easterly winds
to reverse or weaken and become westerly
winds. El Nino causes climate effects around
the world.
Peruvian fishermen noticed that the arrival of
El Nino often coincided with the Christmas
season so named the phenomenon after the
"the baby boy" Jesus. The warmer water of El
Nino reduced the number of fish available to
catch. The warm water that causes El Nino is
usually located near Indonesia during non-El
Nino years. However, during periods of El Nino
the water moves eastward to lie off the coast
of South America.
El Nino increases average ocean surface water
temperature in the region. This mass of warm
water is what causes climatic change around the
world. Closer to the Pacific Ocean, El Nino
causes torrential rains across the west coast of
North America and South America.
34
Lake Effect Snow:
Lake-effect snow is produced during cooler atmospheric conditions when cold winds move across long expanses
of warmer lake water, providing energy and picking up water vapor which freezes and is deposited on the
leeward shores.
The most likely setting for this localized type of snowfall is when very cold Arctic air rushes over warmer
water on the heels of a passing cold front, as often happens in the Great Lakes region during winter.
Winds accompanying Arctic air masses generally blow from a west or northwest direction, causing lake effect
snow to fall on the east or southeast sides of the lakes.
Whether an area gets a large amount of snow from lake effect is dependent on the direction of the winds, the
duration they blow from a particular direction, and the magnitude of the temperature difference between the
water and air.
35