The document summarizes key concepts about atmospheric and oceanic circulation. It discusses how air pressure, temperature, and density are related, and how changes in one can impact the others. It explains the three main forces that influence wind patterns - the pressure gradient force, Coriolis force, and friction. The interaction of these forces determines global wind circulation and ocean currents. Specific circulation patterns discussed include the Hadley cell, jet streams, monsoons, and the ocean's thermohaline circulation.

1. Chapter 4
Atmospheric and Oceanic
Circulation
Or: What goes around, comes around.

2. Air Pressure and Wind

3. Air Pressure and Wind

4. Have you ever noticed
changes in air pressure?

5. Have you ever noticed
changes in air pressure?

6. Have you ever noticed
changes in air pressure?

7. What is air pressure?

8. What is air pressure?
Pressure is the force a gas exerts on some specified area
of a container--it is the result of molecular collisions
between the gas and the container

9. Air pressure changes with altitude, from
place to place—and even in the same place,
changes over time

10. Air pressure changes with altitude, from
place to place—and even in the same place,
changes over time

11. Pressure, Density, and Temperature
 Pressure (P), density (D), and temperature
(T) are all interrelated
 Pressure is the force of molecular collisions per
unit area (lbs/in2)
 Density is the weight of a material per unit
volume (g/m2)
 Temperature is a measure of molecular motion
 Changes to one of these variables can cause
changes in the others
For example….

12. Changing Density Pt.I
• There are three ways to change
the density of a gas:
1.Change the size of the container
What happens to pressure?
What happens to temperature?

13. Changing Density—Pt. II
2. Add or subtract molecules
What happens to the temperature of the balloon
when it’s blown up?
What happens to the pressure inside the balloon
when it’s blown up?
What happens to the pressure when it’s let go?

14.  What happens when you change the
temperature of a confined gas?
 Let’s take our original container full of
molecules and heat it up!

15. - What’s happening to the pressure?
- Is density changing, or not?

16. A little simplification:
 For confined gases:
(if D↑ then P↑)
(if D↑ then T↑)
(if P↑ then T↑)
(if T↑ then P↑--but only if confined)
Note:
(changing T will NOT affect D, if confined)

17. Changing Density—Pt.III
3. Change its
temperature (if it is
uncontained)
- What will happen
to the density?
- How will pressure
be affected?

18. Changing Density—Pt.III
3. Change its
temperature (if it is
uncontained)
- What will happen
to the density?
- How will pressure
be affected?

19. In the atmosphere, gases are
uncontained, like this…

20. A little more simplification:
 For unconfined gases (like in the
atmosphere):
(if T↑ then D↓)
(if D↓ then P↓)
(if D↓ then T↓)

21. Measuring
Atmospheric Pressure

22. Measuring
Atmospheric Pressure
 In 1643 Evangelista Torricelli (a student
of Galileo) invented the first barometer…

23. Measuring
Atmospheric Pressure
 In 1643 Evangelista Torricelli (a student
of Galileo) invented the first barometer…

24. Measuring
Atmospheric Pressure
 In 1643 Evangelista Torricelli (a student
of Galileo) invented the first barometer…
 Today, we use an aneroid barometer

25. Measuring
Atmospheric Pressure
 In 1643 Evangelista Torricelli (a student
of Galileo) invented the first barometer…
 Today, we use an aneroid barometer

26. Average Sea Level Air
Pressure
 29.92 in. (inches of mercury)
 14 lbs/in2
 1013.2 mb (millibars of mercury)
 101.32 kPa (kilopascals, where 1
kilopascal is equivalent to 10 millibars)
We will use millibars, as this is the most
commonly used unit of measurement

27. Isobars
 Lines on a map that connect points of
equal barometric pressure are called
isobars
 Isobars follow the same rules as other
iso- lines (don’t cross, form closed
shapes, etc.)

28. Isobaric Maps

29. Isobaric Maps

30. The Pressure Gradient Force

31. Wind
 Wind—Air moving horizontally in
response to pressure differences
 The process is called advection

32. Convection Cell Diagram
 Draw the convection cell diagram and
label it, just like you see it on the board
 Practice drawing a simplified version to
help you remember “out of the high,
into the low” on exam day

33.  Air always moves from regions of
higher air pressure to regions of
lower air pressure
 In other words:
“Out of the High, Into the Low!”

34. Local Winds
Convection Cells in Motion
 Land and Sea Breezes
 Mountain and Valley Winds
 Katabatic Winds (a.k.a. Mistral)
 Chinook Winds (a.k.a. Santa Anas,
Diablo Winds, Foehn winds, etc.)

35. Wind Direction

36. Wind Direction
 Wind direction is determined by where
the wind is coming from

37. Wind Direction
 Wind direction is determined by where
the wind is coming from
 For example, an east wind is one that is
coming from the east

38. Wind Direction
 Wind direction is determined by where
the wind is coming from
 For example, an east wind is one that is
coming from the east
 A sea breeze is one that is coming from the
sea and moving toward the land

39. Sea Breeze

40. Land Breeze

41. Valley Breeze

42. Mountain Breeze

43. Chinook/Santa Ana Winds

44. 3 Forces Affecting Air in
Motion
 Pressure Gradient Force
 Coriolis Force
 Friction

45. Force #1:
The Pressure Gradient Force

46. Force #1:
The Pressure Gradient Force
 The pressure gradient force is the force
exerted by a gas (in this case, air) at higher
pressure trying to move to an area of lower
pressure

47. Force #1:
The Pressure Gradient Force
 The pressure gradient force is the force
exerted by a gas (in this case, air) at higher
pressure trying to move to an area of lower
pressure
 The PGF pulls air out of the high and into the
low at a 90º angle relative to the isobars

48. Force #1:
The Pressure Gradient Force
 The pressure gradient force is the force
exerted by a gas (in this case, air) at higher
pressure trying to move to an area of lower
pressure
 The PGF pulls air out of the high and into the
low at a 90º angle relative to the isobars
 The greater the “slope”, or gradient, between
one pressure region and the next, the faster
the air will move

49. Where the Isobars are Close Together,
Winds are Faster & Stronger

50. Where the Isobars are Close Together,
Winds are Faster & Stronger
HEY… Hold ON.
What’s UP with the curving motion?

51. Force #2:
The Coriolis Force
 A force which causes fluids in motion
over great distances and objects
moving at high speed to be deflected:
 to the right in the Northern Hemisphere
 to the left in the Southern Hemisphere.
(Note: Air acts like a fluid in many ways.)

52. PGF + Coriolis Force =
“curving” wind

53. Coriolis Force—doing the math
 The Coriolis force is a force existing in a
rotating coordinate system with constant
angular velocity to a reference frame. It
acts on a body moving in the rotating
frame to deflect its motion sideways.

54. Formulae (for the mathematically advanced)
 In non-vector terms: at a given rate of rotation of the observer, the
magnitude of the Coriolis acceleration of the object is proportional to the
velocity of the object and also to the sine of the angle between the
direction of movement of the object and the axis of rotation.
 The vector formula for the magnitude and direction the Coriolis
acceleration is
where (here and below) is the velocity of the particle in the rotating
system, and is the angular velocity vector (which has magnitude equal
to the rotation rate and is directed along the axis of rotation) of the
rotating system. The equation may be multiplied by the mass of the
relevant object to produce the Coriolis force:
 The × symbols represent cross products. (The cross product does not
commute: changing the order of the vectors changes the sign of the
product.)
 The Coriolis effect is the behavior added by the Coriolis acceleration. The
formula implies that the Coriolis acceleration is perpendicular both to the
direction of the velocity of the moving mass and to the rotation axis.

55.  A force which causes fluids (and air) in
motion over great distances and objects
moving at high speed to be deflected
 to the right in the Northern Hemisphere
 to the left in the Southern Hemisphere.

56. Coriolis Force: In The Toilet
 Is it valid to assume that the water in
your toilet, sink, or bathtub will be
deflected to the right while draining?

57.  A force which causes fluids in motion
over great distances and objects
moving at high speed to be deflected
 to the right in the Northern Hemisphere
 to the left in the Southern Hemisphere.

58.  A force which causes fluids in motion
over great distances and objects
moving at high speed to be deflected
 to the right in the Northern Hemisphere
 to the left in the Southern Hemisphere.

59. Geostrophic Winds

60. Geostrophic Winds
 When the Coriolis Force and Pressure
Gradient Force balance one another,
winds spin around a high or low
pressure cell, parallel to the isobars

61. Geostrophic Winds
 When the Coriolis Force and Pressure
Gradient Force balance one another,
winds spin around a high or low
pressure cell, parallel to the isobars
 These winds occur in the upper
atmosphere, where there is no friction

62. Geostrophic Winds
 When the Coriolis Force and Pressure
Gradient Force balance one another,
winds spin around a high or low
pressure cell, parallel to the isobars
 These winds occur in the upper
atmosphere, where there is no friction
 They are known as geostrophic
winds

63. Geostrophic winds

64. Force #3:
Friction

65. Putting it together:
3 Forces Affecting Air in Motion

66. Putting it together:
3 Forces Affecting Air in Motion

67. Surface winds:
Make a simple drawing

68. Surface winds:
Make a simple drawing
 Be able to draw it in your sleep...

69. Northern Hemisphere and
Southern Hemisphere Winds

70. Convergent and Divergent Air

71. Hadley Cells

72. A Simplified Global Circulation
Model

73. The ITCZ

74. Subtropical Highs

75. Some are so prominent, they even
have their own special names

76. Between the ITCZ and the SHPs
are the Trade Winds

77. The Hadley Cell at Work

79. The Westerlies

80. Subpolar Lows

81. Polar Easterlies

82. Polar Highs

83. A Simplified Global Circulation
Model

84. The Jet Stream(s)

85. Rossby Waves:
Undulations in the Jet Stream

86. World Regions with Monsoon Patterns

87. Monsoons in India and Asia

88. Minor Monsoons: Australia and W. Africa

89. Seasonal Movement of the ITCZ

90. Seasonal Pressure Changes
Cause Seasonal Wind Changes

91. ITCZ shifts more dramatically over
land than it does over water

92. Multi-year Atmospheric Oscillations
• ENSO--El Niño-Southern Oscillation
– Ocean-Atmosphere connection
• (we will discuss this phenomenon in Chapter 7)
• NAO--North Atlantic Oscillation
– Affects Europe, eastern US, Greenland/
Canada region; no defined pattern
• AO--Arctic Oscillation
– Associated with NAO
• PDO--Pacific Decadal Oscillation
70

93. El Niño/Southern Oscillation
(ENSO)

94. El Niño/Southern Oscillation
(ENSO)

95. NAO--Positive Phase
• Stronger Azores
high and deeper
Icelandic low
• Stronger winter
storms, more of
them to the north
• Mild, wet eastern
U.S.; warm, wet in
N. Europe
• Cold, dry Med.,
west Greenland,
NE Canada 72

96. NAO--Negative Phase
• Weaker Azores
high, Icelandic low
• Reduced PGF =
weaker storms and
less of them
• Cold snaps in
eastern U.S. bring
more snow; cold,
dry in N. Europe
• Wetter Med.;
Greenland, NE
Canada milder 73

97. Ocean Currents
• Forces driving ocean currents
– Frictional drag of wind
– Coriolis force
– Temperature, density, and salinity differences
– Location of contents and shape of the sea floor
– Tides
74

98. Warm and Cold Surface Currents
• Direction and temperature

99. Upwelling Currents
• Where the net movement of water is away
from the coast, cold, dense water rises up
from the bottom of the ocean to replace
the water that has moved away.
76

100. Downwelling Currents
• Where the net movement of water is
toward the coast, warmer surface water
piles up and pushes down toward the
bottom of the ocean, displacing colder
water, below.
77

101. Open-ocean Upwelling
• Near the equator,
upwelling occurs
where surface winds
cause ocean water to
diverge. As surface
waters move apart,
cold bottom water rises
up to replace what’s
been pushed away.
78

102. Currents: Thermohaline Circulation