1. 1. What does “stability” mean in the atmosphere. 2
1.What does “stability” mean in the atmosphere? 2.Hydrostatic equilibrium represents a balance between what two forces acting on the atmosphere? 3.What does adiabatic cooling mean? 4.How is adiabatic cooling different from environmental lapse rate? 5.What is the dry adiabatic lapse rate? A. 10°C / 1000m or 5.5°F / 1000ft B.3.3°F/1000 ft or 6°C /1000m C. 3.5°F/1000ft or 6.4°C/1000m

2. 6. What is the wet adiabatic lapse rate?
A. 10°C / 1000m or 5.5°F / 1000ft B.3.3°F/1000 ft or 6°C /1000m
C. 3.5°F/1000ft or 6.4°C/1000m
7.If the ELR > WAR and DAR, the atmosphere is :
A. stable B. unstable C. conditionally stable
8. If the ELR < WAR and DAR, the atmosphere is :

3. PRESSURE & WIND, GENERAL CIRCULATION, JET STREAMS

4. FORCES that move AIR: Winds Aloft: (top of troposphere) 1. Gravity
2. Pressure gradient
3. Coriolis effect
Surface Winds:
1. Gravity
2. Pressure gradient
3. Coriolis effect
4. Friction

5. 1. Gravity
Earth exerts gravitational force on atmosphere. (This causes pressure and density to be greater closer to earth.) Acceleration due to gravity = 9.8 m/sec2

6. 2. Pressure Gradient a) Vertical (Remember hydrostatic equilibrium)
997
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1000
surface

7. 2. Pressure Gradient
b) Horizontal (wind)
Pressure Gradient Force (PGF)
Applied perpendicular to isobars
Inversely proportional to density
PGF is perpendicular to isobars.

9. high wind speed.
low wind speed.
Wind speed determined by steepness of gradient.

11. Current weather map

12. 3. Coriolis Effect / Force
Apparent deflection of moving object due to rotation of earth.
Movement of air masses (high to low) occurs with respect to a grid (lat and long on a rotating surface.

13. Animation

14. Deflection…
1. Is to the right of the path of motion in the northern hemisphere and to the left of the path of motion in the southern hemisphere. 2. Increases with latitude: maximum at poles; zero at equator Plane of deflecting force is parallel to earth’s surface at poles; no component of deflection parallel to surface at equator.

16. Deflection...
3. Increases with wind speed. 4. Increases with mass of object.

17. CE is perpendicular to path of motion
CE is perpendicular to path of motion. If PG and CE were only forces on atmosphere, wind would blow parallel to isobars.
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1000

18. 4. Friction
Surface provides friction to atmospheric movement; “slows down” the air.

19. Friction and Surface Winds
Drag produced by surface. Frictional force is applied opposite to direction of air motion; causes wind to blow across the isobars.

24. Minimal friction aloft > 3000 ft in troposphere “friction layer” : 0 – 3000 ft
Winds aloft blow parallel to isobars: geostrophic wind

25. geostrophic balance
Show air parcel moving in response to pressure gradient, then deflected, as in Fig 8.9 , until pressure gradient force and Cor effect are in opposite directions; eventually this balance is reached : “Geostrophic balance”; the resulting wind is geostrophic wind and it is parallel to isobars;
(Note: Coriolis effect is to the right of MOTION not to the right of gradient; define geostrophic balance as” balance between pressure gradient and Coriolis forces acting on a parcel so that the forces are equal in magnitude but in opposite directions; wind produced is geostrophic.)
“balance between pressure gradient and Coriolis forces acting on a parcel
so that the forces are equal in magnitude but in opposite directions”

26. GEOSTROPHIC WIND
Northern Hemisphere L H
Around and clockwise
Around and counterclockwise
Southern Hemisphere L H
Around and clockwise
Around and counterclockwise

29. How do surface winds differ from these upper tropospheric winds?

30. Friction and Surface Winds
Drag produced by surface. Frictional force is applied opposite to direction of air motion; causes wind to blow across the isobars.

31. At surface, friction reduces wind speed, which reduces Coriolis effect.
Coriolis can not balance PGF so wind crosses isobars.

32. Southern hemisphere PG CE
HIGH

33. Resulting wind direction:PG
Southern hemisphere
Out and
counterclockwise
WIND
HIGH
FRIC CE

34. S. hem, HIGH
HIGH

35. Southern hemisphere PG CE
LOW

36. Southern hemisphere CE PG
In and
clockwise
LOW

37. S. hem, LOW
LOW

38. Northern hem, HIGH
Out and
clockwise
HIGH

39. Northern hem, LOW
In and
counterclockwise
LOW

41. General Circulation

42. Global Wind Systems driven by Highs and Lows at surface
Where are Highs and
Lows?

43. Imagine the earth with no rotation
HIGH
There would be a single
cell of convection in each
hemisphere
LOW

44. But the earth rotates Coriolis deflection causes air to be deflected
from those simple
convective pathways
Creating 3 cells in each
hemisphere and a surface
High Pressure in subtropics

45. Let’s look at SURFACE
Components of each cell

46. Hadley Cells Strong and persistent Warm air rising at
Intertropical Convergence
Zone (ITCZ)
At top of troposphere,
spreads poleward, sinks at
Subtropical Highs
Blows towards ITCZ at
Surface, creating…

47. Trade Winds Between subtropical Highs and ITCZ NE in N. Hem
SE in S. Hem

48. Ferrel cells Not as strong, persistent, well- defined

49. Westerlies (surface component of Ferrel cells)
35o - 60o N & S
not steady or persistent

50. Polar Front Zone 60o - 65o N & S
zone of conflict between differing air masses

51. Polar Easterlies 65o - 80o N & S
more prevalent in Southern, variability in Northern

52. Distribution of land masses disturbs this idealized
system of Highs, Lows, winds
Why?
Uneven heating of land and water creates temperature differences
and therefore pressure differences over land vs water with seasonal changes

53. Canadian High
Siberian High
Icelandic Low
Aleutian Low
Azores Bermuda High
Pacific High

54. Pacific High
Azores Bermuda High
Monsoonal Low

55. Upper Air Movement

56. 500
625
Isobaric
surfaces
750
875
1000
City
City
COOL
HEAT

57. DECREASED DENSITY
INCREASED DENSITY
It takes a shorter column of cold air to exert the same surface pressure as a tall column of warm air.
500
625
500
625
750
750
875
875
1000
1000
HEAT
COOL

58. Hot Cold 2300 meters 500 Constant Pressure Map (isobaric maps) 625 750
850
750
850
1000
1000
Hot
Cold

59. Constant pressure map shows elevation of a certain pressure.
Low heights and troughs
represent cold air.
High heights and ridges
represent warm air.

60. 5400
5520
5580
5640
5700

62. Currently: Current surface temperature map
Current map of heights of 500 mb layer

63. Constant Altitude Map
Shows pressure at a given altitude

64. 500
625
550 mb
750
810mb
500
1000m
1000m
1000m
625
850
750
850
1000
1000
Hot
Cold

65. On a constant altitude map:
low pressures indicate Cold Air
high pressures indicate Warm Air

66. High heights on a constant pressure surface map are equivalent to high pressures on a constant altitude map
Low 500 mb heights are associated with low pressure at any given altitude;
High 500 mb heights are associated with high pressure at any given altitude.

67. Therefore, high and low heights tell you where high and low pressures are (for a given altitude)

68. Upper Level Winds Westerly in mid- and high latitudes Easterly
(20°-90° N & S)
Easterly
in Tropics (15°N - 15°S)

69. Upper Level Westerlies have ridges and troughs:
“Rossby Waves” (Longwaves)
Wavelength = 1000s km
3 - 6 loops around earth
above 500 mb layer
influence surface weather

70. c

72. Converging height lines make wind speeds increase

75. On warm side, pressure drops less rapidly with altitude than on cold side; Note isobaric surfaces slope and slope increases with altitude

76. Therefore, wind speed increases with altitude
JET STREAMS : zones of high wind speed (Narrow bands, speed increases toward center (up to 150 mph))
Embedded in upper level Westerlies
below tropopause
Jet streams are located above strong temperature contrasts at surface

77. Polar Jet Stream
Subtropical Jet Stream

78. Polar Front Jet Stream
Between midlatitude tropopause and polar tropopause

79. Polar Jet above Polar Front Zone :
Where cold dense polar air meets warmer air from mid-latitudes

82. Can see polar jet on 300 mb maps
Current 300 mb map

83. Subtropical Jet Stream
Between midlatitude tropopause and tropical tropopause

85. Subtropical Jet due to Conservation of Angular Momentum:
greatest wind speed at North edge of Hadley cell
due to Conservation of Angular Momentum:
(smaller radius of rotation, faster the spin)

86. Enhanced warming in Arctic is affecting Rossby waves

87. Highs and Lows move horizontally
Highs move towards convergence aloft
Surface pressure rises in direction High is moving and falls in its wake
Rising barometer means air is being ADDED aloft and sinking air (clear skies) are coming