High and Low Pressure Weather Systems

1. High and Low Pressure Weather Systems

2. Air (Atmospheric) Pressure • Is the force exerted by air particles • Air moves from an area of high pressure to an area of low pressure. • The moving air is called wind.

3. Air Pressure is always changing and depends on factors such as: • Temperature/Time of day - hotter air has higher pressure • Altitude – higher up = lower pressure • Humidity – higher = lower pressure • Migrating weather systems – Highs and Lows

4. Low Pressure Systems • Bring cloudy, rainy or stormy weather. • Warm air is forced up. • As it rises, the air spins • As the air rises, it also cools and water vapor condenses to form clouds.

5. Low pressure systems can cause stormy weather and extreme weather events like cyclones, hurricanes and typhoons

6. Represented on a weather map by: • isobars with an “ L ” written in the central most isobar • arrows traveling clockwise in the Southern Hemisphere or counter-clockwise in the Northern Hemisphere

7. High Pressure Systems • Bring clear blue skies, calm winds, cooler temperatures and lower chance of precipitation. • Drier air usually results in a greater range of high and low temperatures • Cold air falls down • As it falls, the air spins • As the air falls, it loses humidity and clear skies are the result

8. Represented on a weather map by • isobars with an “H” in the central most isobar • arrows showing which direction the wind is flowing (clockwise in Northern Hemisphere, counter-clockwise in the Southern Hemisphere).

9. Highs and Lows on Weather Maps

10. The Coriolis Effect • Caused by the Earth’s rotation • Results in the curving of moving objects, including air • It is one thing that causes wind and the direction of prevailing winds that exist in each major latitude belt

11. Prevailing Wind • The direction the wind blows most of the time in a certain location

12. Jet Streams • Narrow currents of fast moving air flowing in the upper levels of the atmosphere • Flow between cold and warm air masses • Usually move weather systems from place to place – always WEST to EAST

13. Northern vs. Southern Hemisphere The direction that the air spins is opposite

14. Highs vs. Lows

15. Highs vs. Lows

16. ADD Clockwise = Anti- Cyclone Counter-Clockwise = Cyclone

17. Highs & Lows on a weather map

18. Review Video • http://www.youtube.com/watch?v=aiYyCurh_SU&safe=active • Fox 9 weather 3:24

19. Question Page – do as notes

20. Question 1 • Why do high pressure systems cause clear skies? • B/c Cool air falls. Cool air does not hold much moisture as warm air, thus preventing the formation of clouds.

21. Question 2 • Why do Low pressure systems cause clouds? • B/c Warm air rises and cools, causing water vapor to condense and form clouds

22. Question 3 • Why do high pressure systems cause weather to stay the same for days? • B/c HP systems are large, usually the size of an entire air mass, therefore they take a longer time to move out of an area.

23. The Crushing Can - videos • Pop Can Crush • http://www.stevespanglerscience.com/experiment/incredible-can-crusher • 55 gallon Barrel Crush • http://www.youtube.com/watch?v=JsoE4F2Pb20&safe=active

24. Assignment • Do the Crushing Can lab pages 41- 42 • Do the Worksheets on pages 44 - 50

25. Page 44 answers • 1. Solar Energy • 2. Clouds • 3. Earth’s Rotation • 4. The Jet Stream • 5. Prevailing Winds • 6. Ocean Currents • 7. Lithosphere • 8. Hydrosphere

26. Page 45 answers 1. Cold, warm, stationary, occluded 2. Warm – moves slow, gentle, warm air moves towards colder air, gentle sloped straight boundary line Cold – moves fast, stormy, cold air moves toward warmer air, steeply curved boundary line 3. Cold fronts – cold air mass over takes a warm air mass 4. High – clear sky, nice weather Low – cloudy, bad weather 5. High – clockwise (NH), falling air, clear, sunny Low – counterclockwise (NH), rising air, clouds, rain

27. Page 46 answers 1. Warm air rises and cools. Water vapor condenses out of the air to form clouds. 2. In A, the warm air is less dense. 3. In B the warm air is forced up by the mtn 4. C 5. A 6. E 7. B

28. Page 46 continued 8. (b) Air Mass 9. (a) Condensation 10. (c) Advective 11. (b) Precipitation 12. (a) Coriolis Effect 13. (b) Jet Streams 14. (c) Polar Easterlies 15. True or False. True – Clouds form when air rises and cools. False – different things can make air to rise (fronts, mountains, etc)

29. Page 47 answers

30. Answers to Highs, Lows and Fronts Worksheet. P. 48 1. 2. A) H = High Pressure System B) Clear, blue sky, sunny, cool, stable, mild wind

31. 3. In terms of fronts – a warm front is arriving, and hence the formation of cirrus clouds • The thick grey blanket are altostratus clouds • By night, it is likely that nimbostratus clouds will have formed and light rain will have begun to occur. • The light rain will continue into the next day b/c warm fronts pass slowly

32. Page 49 answers • B 2. C 3. A 4. a) NE b) SE

33. Page 49 Question 5 Page 49 question 5

34. Page 50 answers • Warm front, Cold Front, Stationary Front • High pressure system, cold air • SE, Cold front • Moving blob of air • Cold Front • Stationary Front • Cold Air Mass • Clear due to High Pressure • Cold air mass passed over; caused snow