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Why Do We Have Why Do We Have Weather? Weather?
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Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Dec 13, 2015

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Page 1: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Why Do We Have Why Do We Have Weather?Weather?

Page 2: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

An IntroductionAn Introduction

What is weather?What is weather?

Weather PatternsWeather Patterns

Weather ForecastsWeather Forecasts

Page 3: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

WHY DO WE HAVE THE WHY DO WE HAVE THE WEATHER ?WEATHER ?

Just think about it!Just think about it! Why is there wind? Why does it blow Why is there wind? Why does it blow

from one direction one day and from one direction one day and another the next?another the next?

Why is it rainy one day and dry the Why is it rainy one day and dry the next?next?

How come it’s cold in the winter?How come it’s cold in the winter? How can we have hail in the summer?How can we have hail in the summer? What causes snow and freezing rain?What causes snow and freezing rain?

Page 4: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Let’s take a look at the weather Let’s take a look at the weather picture and why we have picture and why we have

weather!weather!

Page 5: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

What is Weather?What is Weather?

State of the atmosphere at a specific time and State of the atmosphere at a specific time and placeplace

Includes such conditions as air pressure, wind, Includes such conditions as air pressure, wind, temperature, and moisture in the airtemperature, and moisture in the air

Temperature is a measure of air molecule Temperature is a measure of air molecule movementmovement– Sun’s energy causes air molecules to move rapidly; Sun’s energy causes air molecules to move rapidly;

temperatures are high and it feels warmtemperatures are high and it feels warm– When less of the Sun’s energy reaches air molecules, When less of the Sun’s energy reaches air molecules,

they move less rapidly and it feels coldthey move less rapidly and it feels cold

Page 6: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Wind Wind

Air moving in a specific directionAir moving in a specific direction As the sun heats air, it expands, becomes As the sun heats air, it expands, becomes

less dense, rises, and has low atmospheric less dense, rises, and has low atmospheric pressurepressure

Cooler air is denser and sinks, causing high Cooler air is denser and sinks, causing high atmospheric pressureatmospheric pressure

Air moves from high pressure areas to low Air moves from high pressure areas to low pressure areas, causing windpressure areas, causing wind

Page 7: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

HumidityHumidity

The amount of water vapor in the airThe amount of water vapor in the air Warmer air can hold more water vapor, tending to Warmer air can hold more water vapor, tending to

make it more humidmake it more humid Relative humidity – the amount of water vapor in the Relative humidity – the amount of water vapor in the

air compared to what it can hold at a specific air compared to what it can hold at a specific temperaturetemperature

When air cools, it can’t hold as much water vapor, When air cools, it can’t hold as much water vapor, so the water vapor condenses to liquid or forms ice so the water vapor condenses to liquid or forms ice crystalscrystals

Dew point – the temperature at which air is Dew point – the temperature at which air is saturated and condensation formssaturated and condensation forms

Page 8: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

If we were to pick one term to help If we were to pick one term to help explain why we have weather, what explain why we have weather, what do you think would be a good word?do you think would be a good word?

You might pick heat or sun….but You might pick heat or sun….but another good choice would beanother good choice would be

ConvectionConvection

Page 9: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Convection is the transfer of Convection is the transfer of heat,heat,

usually in gases or liquids.usually in gases or liquids.

Page 10: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

After the atmosphere is warmed by radiation After the atmosphere is warmed by radiation and conduction, the heat is transferred and conduction, the heat is transferred

throughout the atmosphere by convection.throughout the atmosphere by convection.

Since warmed air has Since warmed air has more space between more space between the molecules, it’s less the molecules, it’s less dense and risesdense and rises

Cooled air is more Cooled air is more dense and tends to sinkdense and tends to sink

In general, air near the In general, air near the equator tends to rise equator tends to rise and air near the poles and air near the poles tends to sinktends to sink

Page 11: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Take a look at this!Take a look at this!

Page 12: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Notice the band of clouds Notice the band of clouds around the equator ?around the equator ?

This is the This is the ITCZITCZ or inter or inter tropical convergence zonetropical convergence zone

Page 13: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Why do you think there is this Why do you think there is this band of clouds near the band of clouds near the

equator?equator?

Page 14: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Did you figure it out?Did you figure it out?

Warm, moist air in the tropics risesWarm, moist air in the tropics rises Cold air can hold less moisture than Cold air can hold less moisture than

warm airwarm air As the moist air rises, it condenses and As the moist air rises, it condenses and

forms clouds!forms clouds!

Page 15: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

CloudsClouds

Clouds form as warm air is forced upward Clouds form as warm air is forced upward and cools. Then water vapor condenses in and cools. Then water vapor condenses in tiny droplets that remain suspended in the airtiny droplets that remain suspended in the air

Shape and height of clouds vary with Shape and height of clouds vary with temperature, pressure, and water vapor in temperature, pressure, and water vapor in atmosphereatmosphere

Page 16: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

CloudsClouds ShapeShape

– Stratus-smooth, even sheets or layers at low altitudesStratus-smooth, even sheets or layers at low altitudes– Cumulus-puffy, white clouds, often with flat basesCumulus-puffy, white clouds, often with flat bases– Cirrus-high, thin, white feathery clouds made of ice crystalsCirrus-high, thin, white feathery clouds made of ice crystals

HeightHeight– Cirro – high cloudsCirro – high clouds– Alto – middle-elevation cloudsAlto – middle-elevation clouds– Strato – low cloudsStrato – low clouds– Nimbus clouds are dark and so full of water that sunlight can’t penetrate Nimbus clouds are dark and so full of water that sunlight can’t penetrate

themthem Precipitation Precipitation – water falling from clouds– water falling from clouds

– When water droplets in clouds combine and grow large enough, When water droplets in clouds combine and grow large enough, precipitation falls to Earthprecipitation falls to Earth

– Air temperature determines whether the droplets form rain, snow, sleep, or Air temperature determines whether the droplets form rain, snow, sleep, or hailhail

Page 17: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

CirrusCirrus

Page 18: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

CumulusCumulus

Page 19: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

StratusStratus

Page 20: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.
Page 21: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Consequences of Rotation: the Coriolis Consequences of Rotation: the Coriolis effecteffect

Page 22: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

The Weather HighwaysThe Weather Highways

The rotation of the The rotation of the earth creates the earth creates the Coriolis effect.Coriolis effect.

The Coriolis effect The Coriolis effect causes the air and causes the air and water to be deflected water to be deflected to the right north of the to the right north of the equator.equator.

This creates global This creates global weather highwaysweather highways

Page 23: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

The WesterliesThe Westerlies

Because of our latitude, Because of our latitude, most of our weather most of our weather comes from the westcomes from the west

Looking at the weather Looking at the weather map, what type of map, what type of weather might we weather might we expect?expect?

What type of weather What type of weather might we expect in a might we expect in a few days?few days?

Page 24: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Let’s break for a short reviewLet’s break for a short review

1.Transfer of heat in liquids or gases_____1.Transfer of heat in liquids or gases_____2. _____ air is dense and tends to sink.2. _____ air is dense and tends to sink.3. Band of clouds found around the 3. Band of clouds found around the

equator______equator______4. Cold air holds _____ moisture than 4. Cold air holds _____ moisture than

warm airwarm air5. The Coriolis effect causes the air and 5. The Coriolis effect causes the air and

water to be deflected to the _____ of the water to be deflected to the _____ of the equatorequator

Page 25: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

How did you do?How did you do?

1.1. CONVECTIONCONVECTION

2. 2. COLDCOLD

3. 3. ITCZITCZ

4. 4. LESSLESS

5. 5. RIGHTRIGHT

Page 26: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Now What?Now What?

Ok, so we know that the weather Ok, so we know that the weather moves around on these highways and moves around on these highways and that warm air rises and cold air sinks.that warm air rises and cold air sinks.

But why is it sunny one day, and rainy But why is it sunny one day, and rainy the next?the next?

Page 27: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Let’s take another look at the Let’s take another look at the weather mapweather map

Notice that there Notice that there are are HH’s and ’s and LL’s on ’s on the mapthe map

There are also blue There are also blue lines with spikes lines with spikes and red lines with and red lines with half circleshalf circles

Let’s take a closer Let’s take a closer look!look!

Page 28: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

High Pressure AreasHigh Pressure Areas When cooler air When cooler air

sinks and is sinks and is warmed, the air can warmed, the air can hold more moisturehold more moisture

This usually means This usually means sunny skies sunny skies

Winds tend to move Winds tend to move clockwise around a clockwise around a highhigh

Page 29: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Low Pressure AreasLow Pressure Areas When warm air rises When warm air rises

and is cooled, the air and is cooled, the air can not hold as much can not hold as much moisturemoisture

Often, these areas are Often, these areas are associated with associated with precipitation and precipitation and stormy weatherstormy weather

Winds tend to move Winds tend to move counter clockwise counter clockwise around the lowaround the low

Page 30: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

So, if you see a big So, if you see a big HH on the on the weather map over the area you weather map over the area you

live, you can expect fair live, you can expect fair weatherweather

Page 31: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

When you see a big When you see a big LL in your in your area, there will probably be area, there will probably be

stormy weatherstormy weather

Page 32: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

These highs and lows move These highs and lows move or less along the jet stream or less along the jet stream and bring us our weather and bring us our weather

changeschanges

Page 33: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Fronts and Air MassesFronts and Air Masses

Because air and moisture move in the Because air and moisture move in the atmosphere, weather is constantly changingatmosphere, weather is constantly changing Air pressure – measured by barometerAir pressure – measured by barometer An air mass is a large body of air whose An air mass is a large body of air whose

temperature and moisture are fairly similar at a temperature and moisture are fairly similar at a given altitude; properties like the part of Earth’s given altitude; properties like the part of Earth’s

surface over which it formedsurface over which it formed Fronts are boundaries separating different air Fronts are boundaries separating different air masses – clouds, precipitation, and storms occur masses – clouds, precipitation, and storms occur

at frontal boundariesat frontal boundaries There are four different air masses that affect the There are four different air masses that affect the

United StatesUnited States

Page 34: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

The Air MassesThe Air Masses

cPcP( continental polar) : cold, dry stable( continental polar) : cold, dry stable cTcT( continental tropical) : hot, dry, ( continental tropical) : hot, dry,

stable air aloft, unstable at the surfacestable air aloft, unstable at the surface mPmP( maritime polar) : cool, moist, ( maritime polar) : cool, moist,

unstableunstable mTmT( maritime tropical) : warm, moist, ( maritime tropical) : warm, moist,

unstableunstable

Page 35: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

This map shows the air mass This map shows the air mass source regions and there pathssource regions and there paths

Page 36: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Ok, now we see the difference Ok, now we see the difference in the air massesin the air masses

Let’s look at the different fronts and their impact on Let’s look at the different fronts and their impact on weatherweather

Can you see the four different types of fronts on the Can you see the four different types of fronts on the map?map?

Page 37: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Warm FrontsWarm Fronts

A warm front is A warm front is warm air warm air displacing cool air displacing cool air

Shallow leading Shallow leading edge warm air edge warm air must “overrun” must “overrun” cold aircold air

These are usually These are usually slow movingslow moving

Page 38: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Cold FrontsCold Fronts

Cold air advances Cold air advances into region of warm into region of warm airair

Intensity of Intensity of precipitation greater, precipitation greater, but short livedbut short lived

Clearing conditions Clearing conditions after front passesafter front passes

Usually approaches Usually approaches from W or NWfrom W or NW

Page 39: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Stationary FrontsStationary Fronts

Surface Surface positions of the positions of the front do not front do not movemove

Often a region Often a region of cloudsof clouds

Page 40: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Occluded FrontsOccluded Fronts

Cold front overtakes Cold front overtakes warm frontwarm front

Involves three air Involves three air masses of different masses of different temperaturestemperatures

Often found Often found

close to the low close to the low pressure centerpressure center

Page 41: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Ready for a little quiz?Ready for a little quiz?

Here we go!Here we go!

Page 42: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

1.1. Winds in a low Winds in a low

pressure pressure system move system move _____ around _____ around the lowthe low LL

Page 43: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

2.2. What type of What type of

front can be front can be found close to found close to point point D D ??

Page 44: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

3.3. Which of these Which of these

fronts would fronts would you expect to you expect to have greater have greater precipitation, precipitation, but be short but be short lived as the lived as the front passes?front passes?

Page 45: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

4.4. Give the name Give the name

of the air mass of the air mass that would that would have the have the following following characteristics:characteristics:

cool, moist, cool, moist, unstableunstable

Page 46: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

5.5.That important weather word That important weather word that refers to the transfer of that refers to the transfer of

heatheat

Page 47: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

6.6.In general, air near the equator In general, air near the equator

tend to_____ ( rise or fall )tend to_____ ( rise or fall )

Page 48: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

7.7.

It causes air and water to be It causes air and water to be deflected to the right north deflected to the right north

of the equatorof the equator

Page 49: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

8.8.Which of the weather highways Which of the weather highways

usuallyusuallycontrols our weather controls our weather

Page 50: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

9.9.

Warm air holds ( more or less ) Warm air holds ( more or less ) moisture than cold airmoisture than cold air

Page 51: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

10.10. If there is a bigIf there is a big

HH on the on the weather map weather map

where you live, where you live, would you would you

expect fair or expect fair or stormy weatherstormy weather

HH

Page 52: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

How did you do?How did you do?

Let’s check the answers!Let’s check the answers!

Page 53: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

AnswersAnswers

1. 1. Counterclockwise Counterclockwise 8. 8. WesterliesWesterlies

2. 2. Cold Cold 9. 9. MoreMore

3. 3. Cold Cold 10. 10. FairFair

4. 4. Maritime polar (mP)Maritime polar (mP)

5. 5. ConvectionConvection

6. 6. RiseRise

7. 7. CoriolisCoriolis

Page 54: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Severe WeatherSevere Weather

Thunderstorms occur inside warm, moist air Thunderstorms occur inside warm, moist air masses and at frontsmasses and at fronts– Warm, moist air is forced rapidly upward, wehre Warm, moist air is forced rapidly upward, wehre

it cools and condensesit cools and condenses– Strong updrafts of warm air and sinking, rain-Strong updrafts of warm air and sinking, rain-

cooled air cause strong windscooled air cause strong winds

Page 55: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

LightningLightning

Movement of air inside a storm cloud Movement of air inside a storm cloud causes parts of the cloud to become causes parts of the cloud to become oppositely chargedoppositely charged

Current flows between the regions of Current flows between the regions of opposite electrical charge, forming a opposite electrical charge, forming a lightning boltlightning bolt

Thunder – lightning superheats the air, Thunder – lightning superheats the air, causing it to expand rapidly and then causing it to expand rapidly and then contract, forming sound wavescontract, forming sound waves

Page 56: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

TornadoTornado

Violent, whirling wind that moves in a narrow Violent, whirling wind that moves in a narrow path over landpath over land

Page 57: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

HurricaneHurricane

Large, swirling, low-pressure system that Large, swirling, low-pressure system that forms over tropical oceansforms over tropical oceans

Page 58: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

BlizzardBlizzard A winter storm with strong winds, cold A winter storm with strong winds, cold

temperatures, and low visibility, that lasts temperatures, and low visibility, that lasts

more than three hours more than three hours

Page 59: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Severe Weather SafetySevere Weather Safety

A National Weather Service WATCH means A National Weather Service WATCH means conditions are favorable for severe weather conditions are favorable for severe weather to developto develop

A warning means that severe weather A warning means that severe weather conditions already existconditions already exist

Meteorologists study and predict weatherMeteorologists study and predict weather National Weather Service makes weather National Weather Service makes weather

mapsmaps

Page 60: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Reading a weather mapReading a weather map ISOBAR= connects areas of equal pressure ISOBAR= connects areas of equal pressure

BAR comes from BARometric pressureBAR comes from BARometric pressure

Page 61: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Reading a weather map...Reading a weather map... Isotherm: Connects areas of equal Isotherm: Connects areas of equal

temperature; therm means temperaturetemperature; therm means temperature

Page 62: Why Do We Have Weather? An Introduction What is weather? Weather Patterns Weather Forecasts.

Weather Station (not on the TV)Weather Station (not on the TV)Weather conditions at specific locationWeather conditions at specific location

Current Conditions!!