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Unit 4 Weather Dynamics Chapter 13 & 14. 1
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Unit 4 Weather Dynamics
Chapter 13 & 14.
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Global Weather DynamicsWeather dynamics is the study of how
the motion of water and air causes weather patterns.Energy from the Sun drives the motion of
clouds, air, and water.
A globe is tilted to represent Earth’s tilt at an angle of 23.5 degrees to the plane of
its orbit around the Sun.
The major components of Earth that influence weather are the atmosphere, the land forms, and water in its solid,
liquid and vapour forms.
About 70% of Earth’s surface is covered by oceans.
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The atmosphere above the oceans and continents contains air, water vapour, and particles of dust and chemicals,
all of which affect weather, especially when the atmosphere is in motion.
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Weather and ClimateWeather is the set of environmental conditions encountered from day to
day.
Climate is the set of environmental conditions averaged over many
years.
A city may have a January climate that is cold, but you could have a
week of mild weather.
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Global GeographyLongitude is the angle measured east or west from the 0 degree line which passes through
Greenwich, England.
The eastern tip of Cape Breton Island is at 60 degrees west longitude.
Latitude is the angle measured north or southof the equator. The border between the US and
our western Canadian provinces is along the49 degree north latitude line.
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The Tropic of Cancer is at 23.5 degrees north latitude. It is the most northerly location reached by the Sun’s vertical rays on the first day of summer, June 21, each year.
The Arctic Circle is at 66.5 degrees north latitude. It is the most northerly location reached by any of the Sun’s rays on the first day of winter, December 21.
In the southern hemisphere we have the Tropic of Capricorn and the Antarctic Circle.
The region between the Tropic of Cancer and the Tropic of Capricorn is referred to as the tropics. Polar regions occur north of the Arctic Circle, and south of the Antarctic Circle.
Most of Canada’s population lives in the mid-latitude region.
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Earth’s Energy Balance
Section 13.2
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Earth’s Energy BalanceAlmost all of the energy used on Earth to sustain life and cause our changing weather systems comes from the Sun. Different types of EM energy are emitted from the Sun.
Without this energy plants would not grow, and the land water and air would not be warm enough for people to survive. The average surface temperature is 15 degrees C.
Energy can be transferred from one place to another by 4 methods:
1) Radiation2) Conduction3) Convection4) Advection
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Radiation is the transfer of energy by means of waves. Unlike water and sound waves, radiation does not need a medium. The waves can travel from the Sun, through space, and reach Earth.
Visible light is an example of energy that can travel through space. Other examples are:1) Radio waves2) Microwaves3) X-rays4) Gamma rays5) Infrared rays
These travel at 300,000 km/s in a vacuum.
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The set of waves that can travel through empty space at the speed of light is called the
electromagnetic spectrum.
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The other methods of energy transfer require particles of matter.
Conduction is the transfer of energy through the collision of particles. Conduction occurs most easily in metals , but also to a smaller extent in rock, sand soil and water.
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Convection and advection are the transfer of energy by the movement of particles in a fluid.
A fluid is either a liquid (water) or a gas(atmosphere).
Convection transfers energy vertically .Advection transfers energy horizontally.
Weather systems involve convection and advection.
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Reflection and Absorptionof Energy
When the EM waves from the Sun reach Earth, some is reflected off the atmosphere and clouds back into
space; some pass through the atmosphere and bounce off Earth’s surface; some get absorbed by the atmosphere, the ground, or the water at the
surface.
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For earth materials, the portion of energy reflected depends on the albedo of the material.
Clean snow has a high albedo, it reflects a lot of incoming energy. Black soil has a low albedo, it absorbs more energy than it reflects.
Any object or material that absorbs energy and becomes warmer is called a heat sink.
Even though water has a higher albedo than land and soil, the oceans are good heat sinks. When solar energy hits water , the water begins to move(convection), and transfer energy deep into the oceans.
Soil and rock are poor heat sinks. Heat is conducted slowly into these materials.
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An important property of all substances is their heat capacity, which is the measure of
how much heat a substance requires to increase its temperature or how much heat it
releases as its temperature decreases.
Water has a high heat capacity. This means it can hold a lot of heat.
The AtmosphereSection 13.4
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The thin layer of gases that surround the earth is the atmosphere.
The atmosphere is where all the weather happens.
The atmosphere acts like a blanket which controls the temperature of the earth.
Atmosphere
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The earth's atmosphere is made up of dust and a mixture of invisible gases. Some of these gases include:
Nitrogen (N2) 78% Oxygen (O2) 21% Other gases: 1% combined
[water vapour, argon, carbon dioxide, neon, helium, krypton, hydrogen, ozone...]
Earth’s atmosphere:
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Nitrogen and ozone act as a protection shield that blocks out harmful radiation from space.
Oxygen is essential for life. Plants produce oxygen and we breathe it in.
Carbon dioxide is essential for life too. We breathe out carbon dioxide and plants breathe it in.
Some of these gases have very important roles in the atmosphere.
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Water vapour is essential to the water cycle and weather patterns.
Water vapour is responsible for clouds, fog, rain and snow.
Note: Even though there is not much water
vapour in the atmosphere it has the greatest effect on the weather.
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The atmosphere can be divided up into distinctive layers. The farther we travel from the earth the thinner the atmosphere gets.
Exosphere Thermosphere Mesosphere Stratosphere Tropopause Troposphere
Layers of the Atmosphere
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Troposphere
• The atmospheric layer closest to Earth’s surface• Up to 16 km at equator, 8 km at the poles• Contains most of the atmosphere’s moisture• Responsible for most of our weather
Tropopause
• Troposphere ends in this thin boundary• Temperature no longer decreases with increasing altitude• Temperature rises here, contains ozone which absorbs UV from the Sun• Higher temperature here helps divide troposphere from stratosphere
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Stratosphere
• Dry layer• From 12 to 50 km• Highest ozone levels• Protects Earth from harmful UV• Temperature increases with altitudeMesosphere
• Temperatures are low (-75oC)• Density of gases is low• 50 km to 80 km
O3
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Thermosphere
• Low density• Molecules have higher energy• Higher temperatures than mesosphere• Temperatures up to 30oC• X-rays absorbed, causing high temps• 80 km to 500 km• Sometimes called ionosphere• Particles charged and produce auroras
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Exosphere
• Outermost layer• Can be called space• Few particles, mainly hydrogen
Note that the temperature of the atmosphere is different at different altitudes. Change in temperature over a distance is called a
temperature gradient.The temperature gradient of the troposphere is -6
oC per 1000 meters.
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Atmospheric PressureAtmospheric pressure is the pressure the air exerts as
gravity pulls it toward the center of Earth.It is greatest at sea level, where the molecules are closet
together.
At higher altitudes atmospheric pressure decreases.
Atmospheric pressure at a particular altitude depends on whether the air is rising or falling. There are two
variations to consider : vertical and horizontal.
Pressure gradient is a measure of the amount the atmospheric pressure changes across a set distance.
Pressure gradients can be vertical or horizontal.
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Atmospheric pressure decreases rapidly as the altitude increases. Mountain climbers and air travellers know about atmospheric pressure.
Weather maps show lines of constant pressure. The gradient is greatest where the lines are
closest together. High and low pressure systems are identified on these maps.
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The most common instrument used to measure atmospheric pressure is the aneroid
barometer. The word aneroid means without liquid.
This instrument consists of an enclosed container with thin metal walls that are sensitive to
pressure changes. A needle attached to the container indicates the pressure.
(air pressure drops and the container expands)An aneroid barometer uses a small, flexible metal box called an aneroid cell. This aneroid
capsule (cell) is made from an alloy of beryllium and copper.
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A barometer is commonly used for weather prediction, as high air pressure in a region indicates fair weather while low pressure indicates that storms are more likely.
If the barometer is falling then deteriorating weather or some form of precipitation will fall, however if the barometer is rising then there will be nice weather or no precipitation.
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Gravity pulls down on all matter.
Gases are matter and gravity pulls down on them.
This is why the troposphere (layer closest to the earth) has 99% of all the gases in the atmosphere.
Atmospheric Pressure Recap
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The atmosphere is made up of areas of different densities.
In some areas the air is compacted very tightly (dense) and is very heavy causing a high pressure area.
Other areas the air is not compacted much at all and the air is very light (less dense) creating a low pressure area.
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The air at high altitudes is much thinner (less dense) creating low pressure and cooler temperatures.
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Prevailing Wind Patterns
Section 13.6
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Sailors discovered that in certain areas the winds tend to blow in the same directions most of the time.
They found that if they sailed south close to the equator the winds would blow to the west (from the east).
As they traveled further north they found that the winds would blow most often to the east (from the west).
This regular pattern of winds is known as prevailing winds.
Early 1800s
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A wind is a movement of air in the atmosphere. Major wind patterns cover large areas and are called prevailing winds. These winds affect weather around the world.
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Winds that affect large areas in regular patterns.
Blowing to the east they called the Northeast trade winds.
The winds blowing from the west (taking them back home) were called the
mid-latitude Westerlies (prevailing Westerlies).
Prevailing Winds
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SIMPLE PREVAILING WINDS MAP: 30º and 60º latitudes
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Heat As the sun heats the air over the equator strong convection currents form.
The hot air rises up and air rushes in from the north and south creating winds toward the equator.
This huge convection current billows out and the air begins to cool and fall down around 30o latitude.
Heat and Spin
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As the air falls some of it returns to the equator but some is deflected northward.
This north flowing air is once again heated
and rises up at about 60o latitude.
This rising air then flows to the north pole where it cools and drops flowing back to the 60o latitude.
We now have three convection currents set-up with air flowing in opposite directions at the surface of the earth.
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Spin The earth rotates east to west.
As the earth spins it deflects the wind. ◦Winds blowing north get deflected to the
right. ◦Winds blowing south get deflected to the
left.
The deflection of the wind caused by the earth's rotation is called the Coriolis effect.
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The Coriolis EffectEarth’s rotation causes anything that moves long distances, such as prevailing winds, to appear to
change direction. This apparent change of direction of a moving object in a rotating system is called the
Coriolis effect.
Viewed above the North pole, Earth rotates eastward or counter clockwise. Objects in the Northern
hemisphere appear to move to the right. In the Southern hemisphere moving objects appear to move
to the left.
From some point in the northern hemisphere, fire a rocket at a target south of your position. Because the Earth is rotating the target moves and the rocket will
miss its target.
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Early explorers like Columbus used trade winds to cross the Atlantic Ocean.
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Prevailing winds are caused by a combination of convection currents and Earth’s eastward rotation.
In the Northern hemisphere....
• Solar energy strikes the equator, heating the air, land, water• This warmed air becomes the equatorial convection current• The warm air rises and expands, leaving a low pressure area• Rising air reaches the troposphere, moving northward• At 30 degrees latitude the cooled air sinks, creating high pressure• Air moves from high to low pressure areas at the equator• The moving air is twisted right as it moves south (Northeast Trade Winds)
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In the Northern hemisphere.....
At 30 degrees latitude some descending air from the equatorial convection current is deflected northward, to an area of low pressure at 60 degrees latitude. This low pressure area is formed by the mid-latitude convection current. The surface air moving northward to the low pressure area twists to the right causing the mid-latitude westerlies.
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At the North Pole the air is cold and dense, so it sinks, creating a high pressure region at the
surface. This surface air moves south, twisting to the right and creating the polar
easterlies.
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A narrow band of spinning air is created in the places where these convection currents rise and fall.
The spinning causes the air to speed up creating a tube of fast moving air known as a jet stream.
The winds of the jet stream travel from west to east and can reach speeds of up to roughly 500 km/h.
Jetstream (Overview)
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Aircraft use this to their advantage when flying form west to east. ◦pick up to a 500 km/h tail wind which
saves time and fuel.
Going from east to west pilots try to avoid the jet streams.
Jet streams go right around the globe and generally steer major weather systems.
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Jet Streams – high speed winds in the troposphereAir moves from higher to lower pressure areas.
The troposphere is thicker at the equator, decreasing northward. So pressures will vary.
We get a high altitude east-ward flowing wind at 30 degrees latitude, and again at 60 degrees latitude. Both air masses twist to the right.
(241 to 482 kilometres per hour)
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Prevailing winds and the jet streams are affected by seasonal changes.
Prevailing winds help to distribute large amounts of solar energy from the equator to colder parts of the world.
Convection currents create a return flow of air southward.
Prevailing winds carry moisture causing rain, snow.
Rising air is warm and moist.Falling air is cool and dry.
At 30 degrees N latitude we have cool, dry air. Many deserts are found in this latitude.
At 60 degrees N latitude two air systems meet and rise giving birth to winter storms.
The HydrosphereSection 13.8
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The HydrosphereAll of Earth’s water, both fresh and salt, forms what is
called the hydrosphere. About 70% of Earth’s surface is covered by water.
Freshwater makes up 2.5% of the total water on Earth. Most of this occurs as polar ice.
The Water CycleEnergy from the Sun causes water to evaporate(liquid to vapour) or ice to sublimate(solid to vapour). The invisible water vapour rises , and when the pressure and temperature decrease, the vapour condenses(vapour to liquid) into fog, mist and clouds.
Sometimes water vapour may do the reverse of sublimation(deposition) and form ice crystals. The precipitation falls and the cycle begins again.
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Major Ocean CurrentsSection 13.9
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In 1992 a container ship in the middle of the Pacific Ocean lost 29 000 bath tub toys over the side. Rubber duckies started washing ashore all over the west coast of North America.
In 1990 in a similar type accident 80,000 pairs of Nike shoes were swept off a Korean ship headed for the United states. Nike shoes started showing up from Hawaii to Oregon and as far north as Alaska.
These two accidents provided valuable information to oceanographers regarding ocean currents.
Rubber Duckies and Nike??
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Another spill occurred in 1999.
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An oceanographer is a scientist that studies ocean currents.
Ocean currents are compared to large conveyor belts that move around the globe.
The ocean currents circulate the sun’s energy from the equator to the poles.
Ocean Currents
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They serve to warm the poles and at the same time cool the waters of the equator.
In other words the ocean current spread out the heat energy all over the earth so that one area doesn't become too hot or too cold.
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The main cause of ocean currents is heating of the ocean by the sun.
At the equator the sun strongly heats the water.
As the water warms is gets lighter (less dense) and begins to rise.
Cooler, denser water sinks and rushes in to replace the warmer water.
What Causes Ocean Currents?
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This movement of water creates enormous convection currents.
We see warm surface currents flowing toward the poles (N & S).
At the same time, we get cold deep water currents flowing toward the equator.
The surface currents are pushed along and steered around the earth by the prevailing winds.
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The warmer the air is above a body of water, the more water it is capable of
holding.◦Evaporation rate is high and clouds form.◦Large amounts of precipitation.
Colder water has cool and dry air above it.◦Weather it brings is cool and dry.
Effects of Ocean Currents
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The Gulf Stream warms the coast of Norway and Iceland.
Ocean currents are like air- the warmer a body of air the greater its ability to hold moisture. The current that reaches Peru is cold so the air above it is cold and dry. We get the Atacama desert on the coast. Where warm waters evaporate, clouds and precipitation form.
Ocean currents keep coastal areas cooler in summer and warmer in winter. We are warmed in winter by warm, moist air of the Gulf Stream.
Ocean currents affect the pressure of the air above them. Air above warm ocean currents rises and forms low pressure systems.
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Average winter temperature for Ottawa is 12° colder than in St. John’s even though Ottawa is further South!
The warm, moist air brought north- ward by the Gulf Stream off the coast of NL is the reason.
Effect on Coastal Areas
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El Niño The phrase El Niño has been around for a
long time.
El Niño was originally just considered a gentle warming of the Pacific Ocean near the west coast of South America.
It usually occurred around Christmas time each year in which local people related the El Niño with poor fishing.
Disruptions to the Current System
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Normally the wind blows off the land in South America pushing away the warm surface water.
The cold nutrient rich water rises up (upwelling) and fish thrive.
During the El Niño wind patterns change and warm surface water is no longer pushed away.
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Since the water is not circulating it cannot cool.
The cold water with all its nutrients is trapped and cannot rise up.
No nutrients getting to the surface means poor fishing and fish kills!
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Normal Year El Niño Year
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During an El Niño year the Pacific Ocean undergoes a greater than normal amount of heating.
The extra heating disrupts and changes the normal patterns of convection currents and wind patterns in the Pacific Ocean.
Bigger Than First Thought…
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A long lasting El Niño effect is believed to affect the weather of the entire planet.
Major shifts in winds and current patterns create weather extremes that bring major ecological, social and economic disruptions world-wide.
The direct cause of El Niño is unknown but it is believed to be connected to global warming.
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During El Niño years the jet stream tends to push further north.
Air north of the jet stream is cooler than air south of the jet stream.
As result North America tends to receive warmer than normal average temperatures.
What does this mean to us?
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During an El Niño year in Newfoundland we would get a warmer winter than normal which would mean more rain and less snow!
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About every four to five years, a pool of cooler-than-normal water develops off South America.
The effects of this cooler water are called La Niña.
This usually shifts the jet stream farther south which steers’ colder drier winters to the Canadian west.
A reversal - La Niña
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For Newfoundland it may bring cooler wetter conditions - lots of snow!
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1. The Sun’s Energy2. Cloud Cover3. Earth’s Rotation4. Jet Streams5. Prevailing Winds6. Ocean Currents7. Land Masses8. The Hydrosphere
All Conditions affecting Weather on a Global Scale (Main Factors):
p. 536 A Global Weather Model
Clouds and FogSection 13.11
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As air rises it begins to cool and expand.
Cooled air can no longer hold all its moisture.
The water vapour begins to condense on dust particles as very tiny water droplets.
Depending on the temperature clouds may be made up of tiny water droplets and or tiny ice crystals.
How Clouds Form
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1. Convective: formed when a land mass is heated and the warmed air begins to rise, expand, cool and water condenses.
We see these types of clouds where thermals and sea breezes are formed.
• When air near the ground is heated• Warm air rises, carrying moisture• At higher elevations air cools• Water vapour condenses, forms clouds• Occurs where solar energy absorbed by water and
other surfaces
Three Main Types of Clouds
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Convective Cloud
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2. Frontal: form at the frontal zone where two
large air masses meet.
The warmer air mass is forced to rise up over the cooler air mass.
It expands and cools resulting in the
formation of condensation.
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Frontal Clouds
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3. Orographic: formed because of geography when air
is forced to rise up a large hill or mountain.
As the wind blows into the side of the mountain it rises up.
As the air rises it expands and cools causing water vapour to condense as clouds.
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Orographic Clouds (an old volcano on one of the Aleutian islands )
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• A cloud that forms near the ground• Can form on cool, cloudless nights• When warm air passes over snow-covered
ground• When moist sea air drifts over a cold current• When moist air rises up a mountain side
Forms when warm moist air moves over a colder surface (land or water) releasing its moisture as very fine water droplets.
Fun in the Fog!
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Cloud shapes tell us about atmosphericconditions.
Two general shapes of clouds:1. Cumulus Clouds2. Stratus Clouds
Classifying Clouds
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Heaped" or "lumpy" clouds result when strong vertical (upward) motions exist in the atmosphere.
This shows us that the air mass is being forced to rise very rapidly.
A clue that the atmosphere is unstable and are usually associated with stormy or severe weather.
Cumulus Clouds
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Wide spread out, smooth, layered clouds.
These clouds gives a clue that the air motion is horizontal (across) rather than vertical (up and down).
The forming clouds are rising slowly which is a sign of a stable atmosphere.
Stratus Clouds
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To further classify clouds, they are named by
altitude in the atmosphere.
Low level clouds have simple names – cumulus and stratus
Medium level clouds – start with prefix alto – meaning higher
Higher level clouds – called cirrus which means curly hair
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stratocumulus
altocumulus
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cumulonimbus
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Evening-May 3,2009
Clouds have a duel role:1) Quite simply clouds act as a blanket.
◦ Cloudy nights: traps heat keeping the air warm. ◦ Clear night sky: heat escapes and air cools
quickly.
2) Keep the earth cool during the day.
◦ The formation of white cloud cover reflects the sun's energy away.
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Cloud Cover Maintains Balance on Earth
When is there a greater risk of frost, on a cloudy night or a clear night?
Deserts regions are so dry that clouds do not form during the day or the night.
What do you think the temperature conditions would be like?
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Questions to Ponder…
