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Why Do We Have Weather? 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.

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Presentation on theme: "Why Do We Have Weather? 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."— Presentation transcript:

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2 Why Do We Have Weather?

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?

4 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

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

6 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

7 Take a look at this!

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

9 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

10 Hadley Cells Caused by convection currents. Caused by convection currents. –Warm air near the equator rises –Cold air near the poles sinks

11 Consequences of Rotation: the Coriolis Effect

12 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 West. The Coriolis effect causes the air and water to be deflected to the West. This creates global weather highways. This creates global weather highways.

13 The Prevailing 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?

14 Combining Hadley Cells, the Coriolis Effect, and Prevailing Westerlies gives you... Tradewinds: Where do you think they got their name? Who were these winds particularly important to?

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

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

17 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?

18 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!

19 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 and clear skies This usually means sunny and clear skies Winds tend to move clockwise around a high Winds tend to move clockwise around a high

20 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 Tornadoes and hurricanes can produce very low pressure readings. Tornadoes and hurricanes can produce very low pressure readings.

21 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

22 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

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

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25 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?

26 Cold Fronts Cold air pushes under a warm air mass. Warm air rises quickly=narrow bands of violent storms form This is the symbol for a cold front

27 Warm Front Warm air slides over departing cold air- large bands of precipitation form This is the symbol on a map for a warm front

28 Occluded Front 2 air masses merge and force warm air between them to rise quickly. Strong winds and heavy precipitation will occur This is the weather map symbol for an occluded front

29 Stationary Front Warm or cold front stops moving. Light wind and precipitation may occur across the front boundary This is the weather map symbol for a stationary front

30 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!

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

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

33 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?

34 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

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

36 6. In general, air near the equator tends to_____ ( rise or fall )

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

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

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

40 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

41 How did you do? Lets check the answers!

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

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