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.
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!
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?
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.)
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.)
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
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
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.)
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.
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
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
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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.
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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.
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