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Why Do We Have Weather?. An Introduction Take good notes! There will be a quiz at the end of this presentation.

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Presentation on theme: "Why Do We Have Weather?. An Introduction Take good notes! There will be a quiz at the end of this presentation."— Presentation transcript:

1 Why Do We Have Weather?

2 An Introduction Take good notes! There will be a quiz at the end of this presentation.

3 WHY DO WE HAVE THE WEATHER ? Just think about it! Just think about it! Why is there wind? Why does it blow from one direction one day and another the next? Why is there wind? Why does it blow from one direction one day and another the next? Why is it rainy one day and dry the next? Why is it rainy one day and dry the next? How come its cold in the winter? How come its 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? video

4 Lets take a look at the weather picture and why we have weather!

5 If we were to pick one term to help explain why we have weather, what do you think would be a good word? You might pick heat or sun….but another good choice would be Convection

6 Convection is the transfer of heat, usually in gases or liquids.

7 After the atmosphere is warmed by radiation and conduction, the heat is transferred throughout the atmosphere by convection. Since warmed air has more space between the molecules, its less dense and rises Since warmed air has more space between the molecules, its less dense and rises Cooled air is more dense and tends to sink Cooled air is more dense and tends to sink In general, air near the equator tends to rise and air near the poles tends to sink In general, air near the equator tends to rise and air near the poles tends to sink

8 Take a look at this!

9 Notice the band of clouds around the equator ? This is the ITCZ or inter tropical convergence zone

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

11 Did you figure it out? Warm, moist air in the topics rises Warm, moist air in the topics rises Cold air can hold less moisture than warm air Cold air can hold less moisture than warm air As the moist air rises, it condenses and forms clouds! As the moist air rises, it condenses and forms clouds! More on this later

12 Consequences of Rotation: the Coriolis effect

13 The Weather Highways The rotation of the earth creates the Coriolis effect. The rotation of the earth creates the Coriolis effect. The Coriolis effect causes the air and water to be deflected to the right north of the equator. The Coriolis effect causes the air and water to be deflected to the right north of the equator. This creates global weather highways This creates global weather highways video video video

14 The Westerlies Because of our latitude, most of our weather comes from the west Because of our latitude, most of our weather comes from the west Looking at the weather map, what type of weather might we expect? Looking at the weather map, what type of weather might we expect? What type of weather might we expect in a few days? What type of weather might we expect in a few days?

15 Lets break for a short review 1.Transfer of heat in liquids or gases_____ 2. _____ air is dense and tends to sink. 3. Band of clouds found around the equator______ 4. Cold air holds _____ moisture than warm air 5. The Coriolis effect causes the air and water in the Northern hemisphereto be deflected to the _____ of the equator

16 How did you do? 1. CONVECTION 2. COLD 3. ITCZ 4. LESS 5. RIGHT

17 Winds Youve read about Global Winds: Youve read about Global Winds: –Trade Winds 0-30° 0-30° –Westerlies Between 30-60° Between 30-60° –Polar Easterlies 60-90° 60-90° –The Doldrums & Horse Latitudes Areas of weak and variable winds Areas of weak and variable winds

18 Local Winds Land surfaces heat up faster than water surfaces Land surfaces heat up faster than water surfaces Sea Breeze: Sea Breeze: –Cool wind from water to land Land Breeze: Land Breeze: –Cool wind from land to sea

19 Valley Breezes Valley Breezes –Warm air from the valley moves upslope –During the day Mountain Breezes: Mountain Breezes: –Cool air descends from the mountains –During the night

20 Now What? Ok, so we know that the weather moves around on these highways and that warm air rises and cold air sinks. Ok, so we know that the weather moves around on these highways and that warm air rises and cold air sinks. But why is it sunny one day, and rainy the next? But why is it sunny one day, and rainy the next?

21 Lets take another look at the weather map Notice that there are H s and L s on the map Notice that there are H s and L s on the map There are also blue lines with spikes and red lines with half circles There are also blue lines with spikes and red lines with half circles Lets take a closer look! Lets take a closer look!

22 High Pressure Areas When cooler air sinks and is warmed, the air can hold more moisture When cooler air sinks and is warmed, the air can hold more moisture This usually means sunny skies This usually means sunny skies Winds tend to move clockwise around a high Winds tend to move clockwise around a high

23 Low Pressure Areas When warm air rises and is cooled, the air can not hold as much moisture When warm air rises and is cooled, the air can not hold as much moisture Often, these areas are associated with precipitation and stormy weather Often, these areas are associated with precipitation and stormy weather Winds tend to move counter clockwise around the low Winds tend to move counter clockwise around the low

24 So, if you see a big H on the weather map over the area you live, you can expect fair weather

25 Surrounding these "highs" and "lows" are lines called isobars. Surrounding these "highs" and "lows" are lines called isobars. – "Iso" means "equal" and a "bar" is a unit of pressure so an isobar means equal pressure. –We connect these areas of equal pressure with a line. Everywhere along each line is constant pressure. –The closer the isobars are packed together the stronger the pressure gradient is.

26 When you see a big L in your area, there will probably be stormy weather

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

28 Fronts and Air Masses An air mass is a large body of air whose temperature and moisture are fairly similar at a given altitude An air mass is a large body of air whose temperature and moisture are fairly similar at a given altitude Fronts are boundaries separating different air masses Fronts are boundaries separating different air masses There are four different air masses that affect the United States There are four different air masses that affect the United States

29 The Air Masses cP( continental polar) : cold, dry stable cP( continental polar) : cold, dry stable cT( continental tropical) : hot, dry, stable air aloft, unstable at the surface cT( continental tropical) : hot, dry, stable air aloft, unstable at the surface mP( maritime polar) : cool, moist, unstable mP( maritime polar) : cool, moist, unstable mT( maritime tropical) : warm, moist, unstable mT( maritime tropical) : warm, moist, unstable

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

31 Ok, now we see the difference in the air masses Lets look at the different fronts and their impact on weather Lets look at the different fronts and their impact on weather Can you see the four different types of fronts on the map? Can you see the four different types of fronts on the map?

32 Warm Fronts A warm front is when warm air is moving towards cold air. A warm front is when warm air is moving towards cold air. The shallow leading edge of warm air must overrun cold air The shallow leading edge of warm air must overrun cold air These are usually slow moving These are usually slow moving

33 Cold Fronts Cold air is moving into a region of warm air Cold air is moving into a region of warm air Intensity of precipitation greater, but short lived Intensity of precipitation greater, but short lived Clearing conditions after front passes Clearing conditions after front passes Usually approaches from W or NW Usually approaches from W or NW animation animation animation

34 Stationary Fronts When neither a warm or cold air mass is moving very much When neither a warm or cold air mass is moving very much Often a region of clouds Often a region of clouds

35 Occluded Fronts Cold front overtakes warm front Cold front overtakes warm front Often found close to the low pressure center Often found close to the low pressure center map http://www.accuweather.com /us/satellite/ei/us_/satellite.asp

36 Ready for a little quiz? Youll need a sheet of paper Write your answers as we go Write your answers as we go Here we go! Here we go!

37 1. Winds in a low pressure system move _____ around the low Winds in a low pressure system move _____ around the low

38 2. What type of front can be found close to point D ? What type of front can be found close to point D ?

39 3. Which of these fronts would you expect to have greater precipitation, but be short lived as the front passes? Which of these fronts would you expect to have greater precipitation, but be short lived as the front passes?

40 4. Give the name of the air mass that would have the following characteristics: Give the name of the air mass that would have the following characteristics: cool, moist, unstable cool, moist, unstable

41 5. That important weather word that refers to the transfer of heat

42 6. In general, air near the equator tend to_____ ( rise or fall )

43 7. It causes air and water to be deflected to the right north of the equator

44 8. Which of the weather highways usually controls our weather

45 9. Warm air holds ( more or less ) moisture than cold air

46 10. If there is a big H on the weather map where you live, would you expect fair or stormy weather If there is a big H on the weather map where you live, would you expect fair or stormy weather

47 How did you do? Lets check the answers!

48 Answers 1. Counterclockwise 1. Counterclockwise 2. Cold 2. Cold 3. Cold 3. Cold 4. Maritime polar (mP) 4. Maritime polar (mP) 5. Convection 5. Convection 6. Rise 6. Rise 7. Coriolis 7. Coriolis 8. Westerlies 9. More 10. Fair


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