1. MET 2204 METEOROLOGY Presentation 4: Wind 1Presented by Mohd Amirul for AMC

2. Recapitulate Lets recap what we have done last week: – What is the Atmosphere? – Composition of Atmosphere – Layers of Atmosphere – Variation in Atmosphere – Air stability 2Presented by Mohd Amirul for AMC

3. Presentation Outline Introduction Convection Gradient Wind General Circulation Friction Jet Stream Local and Small Winds Wind Shear Wind Pressure Systems and Weather Conclusion Part 1 Part 2 3Presented by Mohd Amirul for AMC

4. Learning Outcomes At the end of this session, student should be able to: – Explain the concept of winds around the earth surface and upper winds. – Understand the relation of winds to pressure patterns and movement of weather system. 4Presented by Mohd Amirul for AMC

5. Introduction Presented by Mohd Amirul for AMC5

6. What is the WIND?? Presented by Mohd Amirul for AMC6

7. Cont. Difference in Temperature Difference in Pressure WIND Presented by Mohd Amirul for AMC7 How?? If the temperature increase, the molecule inside the box will move rapidly. Then there are more and rapid collision happen between the molecule and wall. Therefore the pressure will increase. From this pressure difference the air will moving and it will create the WIND.

8. Convection Presented by Mohd Amirul for AMC8

9. Convection : transmits heat by transporting groups of molecules from place to place. Convection occurs in fluids such as water and air, which move freely. Presented by Mohd Amirul for AMC9 Cont.

10. Two surface are heated unequally – Warm air less dense and lifting to the top Spreads and cool – Cold air more dense and drawn to the ground Presented by Mohd Amirul for AMC10 Cont.

11. The horizontal air flow in convective current is WIND. (sometime called ad ADVECTION) Presented by Mohd Amirul for AMC11 Convective current Cont.

12. General Circulation Presented by Mohd Amirul for AMC12

13. steep pressure gradient (fast winds) shallow pressure gradient (slow winds) pressure distance pp nn nn Pressure Gradient Force (PGF) Idea:

14. Pressure difference- create the FORCE and to drive the wind. The force we call as PGF. PGF: The difference in atmospheric pressure per unit distance Wind move from HIGHER PRESSURE to LOWER PRESSURE by PGF. Presented by Mohd Amirul for AMC14 Cont.

15. On the Isobars: – When there is difference in pressure the air begins to moving from higher pressure to lower pressure. Presented by Mohd Amirul for AMC15 Usage of ISOBAR on determine wind speed, strength, and direction. Cont.

16. Closer the spacing of isobars, stronger the PGF. Therefore stronger and faster the WIND. Widely space isobar – create light/slow wind Closely space isobar – create strong/fast wind Therefore general idea of wind speed can get from isobar. Presented by Mohd Amirul for AMC16 Cont.

17. Surface pressure – Low in warm region (equatorial) – High in cold region (poles) Because of PRESSURE DIFFERENCE- create PGF Therefore, PGF develop from poles to equatorial. Presented by Mohd Amirul for AMC17 Cont.

18. Imagine that earth didn’t rotate. Therefore PGF is the only force acting on WIND. – Circulation happen between two hemisphere (Circulation Process): Cold air SINK at poles Because dense air flows from poles to equator, wind will blow straight from poles to equator. Because less dense air rising, warm air force upward at the equator. High level wind blow directly toward the poles. Presented by Mohd Amirul for AMC18 Cont. Convective Current

19. However above circulation is distorted since the earth does ROTATE!!!! So the PGF is not only force acting on the WIND. Presented by Mohd Amirul for AMC19 Cont.

20. Coriolis Force (Geostrophic Force) Idea: – Imagine the rotation of the compact disk when the song played. Try draw a line during the rotation. Then stop the disk. – Now you can see the line you draw is deflected away. Not a straight LINE!! – This is the concept of Coriolis Force. Presented by Mohd Amirul for AMC20

21. Coriolise Force (Geostrophic Force) is the force caused by rotation of the earth It will make a moving mass of air turn to the right at northern hemisphere It will make a moving mass of air turn to the left at southern hemisphere. The angle of deflection/turn directly proportional to wind speed. Presented by Mohd Amirul for AMC21 Cont.

22. Presented by Mohd Amirul for AMC22 Cont.

23. In this course we will concentrate on Northen Hemisphere where mass of air will deflect to the right. Coriolis Force varies from equator to poles: – Maximum at poles and minimum at equator. So it will effect wind direction everywhere except at the equator. Presented by Mohd Amirul for AMC23 Cont.

24. Differences of Coriolis and PGF Pressure Gradient Force Force created by different pressure Wind blow perpendicular to isobar Coriolis Force Apparent deflection result from earth rotation Wind blow parallel to isobar Presented by Mohd Amirul for AMC24

25. PGF drives wind perpendicular to isobars (higher pressure to lower pressure). GF (coriolis force) drives wind to the right until defelected to 90˚ and become perpendicular to isobars. At this time, GF and PGF is BALANCE!!! Presented by Mohd Amirul for AMC25 Geostrophic Wind

26. Geostrophic Wind is the wind that blows when the GF is balance with PGF. Geostrophic wind directly proportional to the PGF. Geostrophic wind speed increase as latitude decrease. (Wind speed becomes faster close to the equator) Presented by Mohd Amirul for AMC26 Cont.

27. Geostrophic winds: go in a straight line go parallel to the isobars have speeds proportional to the pressure gradient force. 1.pressure difference starts wind 2.wind gets going a little, starts being deflected by Coriolis force 3.wind goes faster in response to pressure difference, 4.gets deflected more by Coriolis Force 5.Eventually, the two balance How Geostrophic wind occur??

28. But within the 15 degrees latitude from the equator GF is ZERO. For the wind to be geostrophic it must occur: – Above the friction layer – At a latitude greater than 15 degrees – When the pressure situation is not changing rapidly – With the isobars STRAIGHT and PARALLEL. Presented by Mohd Amirul for AMC28 Cont.

29. Gradient Wind The gradient wind occurs when the isobars are curved. The force makes the wind follow a curved path parallel to the isobars. Gradient wind is due to a combination of 3 forces: – PGF – GF (Coriolis Force) – Cyclostrophic Force Presented by Mohd Amirul for AMC29

30. Cyclostrophic force acts towards the center of pressure system when the isobars are curved. Presented by Mohd Amirul for AMC30 Cont.

31. Friction Presented by Mohd Amirul for AMC31

32. Idea: – Consider two boxes of wood contact with each other. Try move each of those boxes in the opposite direction. It will slow the movement or hardly to move smoothly because of FRICTION FORCE. Friction act as the resistance when one body is moved in contact with another. Presented by Mohd Amirul for AMC32 Cont. V FrFr

33. Same goes with wind. There will be a friction between wind and terrain. It will slower the wind. Friction Layer: Greatest near and right at the surface. Usually confined to lowest 1000m (3000 ft). The friction increase when: – Rougher the terrain – Stronger the wind speed Presented by Mohd Amirul for AMC33 Cont.

34. Friction acting OPPOSITE in wind direction Friction increase will result decrease in GF. Presented by Mohd Amirul for AMC34 Cont.

35. Therefore, the friction will result: GF and PGF no longer in balance!! Friction on sea less than from land. Presented by Mohd Amirul for AMC35 Cont.

36. PGF + GF + Friction Chronology Presented by Mohd Amirul for AMC36

37. Just a Pressure Gradient Start with just a pressure gradient Then wind blows straight from High P to Low P And accelerates as it goes HL View from top Pressure 1017 1015 1013 1011 1009 1007 1005 return

38. Just a Pressure Gradient The wind would blow at the same speed regardless of altitude. H L Pressure 1013 1011 1009 1007 1005 return

39. Now add Friction Then wind still blows straight from High P to Low P, but it doesn’t get moving as fast as soon, especially near the ground HL View from top Pressure 1017 1015 1013 1011 1009 1007 1005 back up

40. Friction and Pressure Gradient Friction slows the wind at the ground—its effects decrease as you go up in the atmosphere. H L Pressure 1013 1011 1009 1007 1005

41. Pressure Gradient and Coriolis Forget friction. The wind starts out straight, but as soon as it starts building up speed, the Coriolis force turns it a bit to the right. HL The wind can’t accelerate any more over here because it’s going parallel to the isobars This is the Geostrophic Wind

42. Reality: Pressure Gradient, Coriolis Force, and Friction Coriolis Force turns the wind some, friction slows the wind some, and the result is roughly a 30º angle between isobars and wind. HL 30º

43. Reality: Pressure Gradient, Coriolis Force, and Friction Friction slows the wind at the ground—its effects decrease as you go up in the atmosphere. H L Pressure 1013 1011 1009 1007 1005

44. Reality: Pressure Gradient, Coriolis Force, and Friction Coriolis Force is turning the wind toward us in the right part of the picture. H L Pressure 1013 1011 1009 1007 1005

45. Reality: Pressure Gradient, Coriolis Force, and Friction Since the Coriolis Force depends on wind speed, its effect decreases toward the ground where the wind speed is slower. H L Pressure 1013 1011 1009 1007 1005 Coriolis Friction

46. Jet Stream In the Troposphere, wind will be stronger (increase in speed) as the height increase. The speed/strength of the wind will be increase to the maximum near tropopause. This maximum wind will concentrate in the narrow band and we call as the JET STREAM. Presented by Mohd Amirul for AMC46

47. Jet stream: narrow band of strong wind at level near the tropopause. Presented by Mohd Amirul for AMC47 Cont.

48. Local and Small Scale Wind (Minor Wind system) Presented by Mohd Amirul for AMC48

49. Before this we dealt with general circulation and major wind system. But now, how the local terrain (e.g. mountain, valley, sea) can affect local weather? Presented by Mohd Amirul for AMC49 Cont.

50. Local winds: Winds that blow over short distances Caused by unequal heating of the earth’s surface within a small area Form only when no winds are blowing from far away Cont.

51. Mountain and Valley Winds During daytime – Air contact with the mountain slope heated from solar radiation. – This air will become warmer than air at the same altitude which are not in contact to the ground (farther from the slope) – The colder air (denser air) will going downward. It will force warmer air near the ground up to the mountain slope. Presented by Mohd Amirul for AMC51

52. – This movement of the air will be called as VALLEY WIND (because air flowing up out of the valley). During night: – Air contact with the mountain slope cooled by terrestrial radiation and becomes heavier (dense) than surrounding air. – It will sinks along the slope – We call the wind as MOUNTAIN WIND (flow like water down the mountain slope) Presented by Mohd Amirul for AMC52 Cont.

53. Mountain Wind stronger than Valley Wind (especially in winter) Presented by Mohd Amirul for AMC53 Cont.

54. Katabatic Wind Katabatic Wind: Any wind blowing down an incline when inclination is influential in causing the wind. Therefore, mountain wind is the katabatic wind. Originated from cold (dense air) spills down slopping terrain displacing warmer air (less dense air ahead of it). Presented by Mohd Amirul for AMC54

55. Land and Sea Breezes Land surface warm and cool more rapidly than water surface. During daytime: – Land will be warmer than sea – Wind will blow from cool (high pressure) to warm land(low pressure) – Therefore, it will blow from sea (cooler) to land (warmer). – We call this wind as SEA BREEZE. Presented by Mohd Amirul for AMC55

56. During night – Wind reverses – Wind will blow from cool land(high pressure) to warmer water (lower pressure) – We call this wind as LAND BREEZE. Land and sea breezes develop only when the overall pressure gradient (change of pressure) weak. – Because wind with a stronger pressure gradient mix the air so rapidly. Thus, local temperature and pressure gradient don’t develop along the shore line. Presented by Mohd Amirul for AMC56 Cont.

57. Presented by Mohd Amirul for AMC57 Cont. Land and Sea Breeze

58. Wind Shear Presented by Mohd Amirul for AMC58

59. Idea: Try rubbing 2 objects against each other. It will create the friction. – If 2 objects are SOLID, they will have no exchange of mass. – If 2 objects are FLUID, they will creates eddy(whirl) along common shallow mixing zone. This shallow layer induce (produce) eddies and mixing is a SHEAR ZONE. *We will discuss more on wind shear and relate with the turbulence in Turbulence chapter. Presented by Mohd Amirul for AMC59 Cont.

60. Presented by Mohd Amirul for AMC60 Cont. Wind Shear

61. Wind shear is defined as a change in wind speed and/or direction within a short distance. it can be in either a horizontal or vertical direction, or both. this change causes a shearing or tearing effect, which causes great concern for pilots and airline industries. Presented by Mohd Amirul for AMC61 Cont.

62. Presented by Mohd Amirul for AMC62 Wind, Pressure System, and Weather.

63. Rising air – Low pressure Bad weather Conducive to cloudiness and precipitate – High Pressure Good weather Because it breaking up the cloudiness and make it scatter. Presented by Mohd Amirul for AMC63 Cont.

64. Stagnant air – When downward motion of air prevent the convection and any upward motion. – Form a stratus (a large dark cloud), fog, haze and smoke. Warm air – Pressure decrease more slowly. Presented by Mohd Amirul for AMC64 Cont.

65. Remember: Low Pressure- Bad Weather High Pressure- Good Weather Presented by Mohd Amirul for AMC65 Cont.

66. Conclusion Wind is the moving air from higher pressure to lower pressure. Isobar provides general information of wind speed and direction. Wind speed and direction influenced by the pressure gradient force, coriolis force and friction. Two major wind systems are gradient wind and geostrophic wind. Jet stream: narrow band of strong wind at level near the tropopause. 66Presented by Mohd Amirul for AMC

67. The local terrain might affect the local wind. Wind shear is defined as a change in wind speed and/or direction within a short distance. Low pressure of air will create bad weather while good pressure of air will create good weather. Presented by Mohd Amirul for AMC67 Cont.

68. Key Points What is the Wind? Concept of Covection How the air move? Use of Isobar The force acting on the wind: PGF, GF, Friction Major Wind: Geostrophic and Gradient Wind Jet Stream Local and Minor Surface Wind: mountain and Valley; Katabati; Land and Sea. Wind Shear 68Presented by Mohd Amirul for AMC

69. End of Presentation #4 5 Minutes for Q/A session 69Presented by Mohd Amirul for AMC

70. Quiz 2 1.What is the air? What is the atmosphere? Is it same? 2.Why tropopause is important in meteorology? 3.What is the solar and terrestrial radiation? 4.Differentiate heat and temperature. 5.How density of air vary with altitude? 6.Define humidity. Duration: 20 minutes Presented by Mohd Amirul for AMC70