ATMOSPHERIC AND

OCEANIC CIRCULATIONS

1. Introduction

2. Mapping pressure variations

3. Causes of pressure variations

4. Driving forces within the atmosphere

5. General circulation of the atmosphere

6. Ocean currents

The original

barometer-

Torricelli’s mercury

barometer.

Source: Christopherson, 2012, p. 133.

Mapping pressure differences: a pressure gradient. Source: Christopherson, 2012, p. 136.

Winds at the coast: daytime. Source: Christopherson, 2012, p. 148.

Winds at the coast: nighttime. Source: Christopherson, 2012, p. 148.

Mountain-

valley wind

systems. Source: Christopherson, 2009,

p. 149.

THIS HAPPENS AT LARGER

SCALES, TOO……..

Example 1: The Asian Monsoon

Example 2: The General Circulation of the

Atmosphere

The Asian monsoon: winter.

Source: Christopherson, 2003, p. 167.

Himalayas/Tibetan

Plateau (cold) HIGH

The Asian monsoon: summer.

Source: Christopherson, 2003, p. 167.

Himalayas/Tibetan

Plateau (warm) LOW

Monsoonal rainfall at

Nagpur, India.

Source: Christopherson, 2012, p. 152.

Nagpur

0°

(equator)

30°N 90°N

(north pole) 60°N 30°S 90°S

(south

pole)

60°S

WARM COLD COLD

Beginnings of the general circulation of the

atmosphere.

CAUTION: the reality is more complicated.

We’re not finished with this yet!

DRIVING FORCES WITHIN THE

ATMOSPHERE

1. Pressure gradient force

2. Coriolis force

3. Friction force

(4. Gravity)

Spiral movements

evident in wind

patterns over the

Pacific Ocean.

Source: Christopherson, 2009,

p. 148.

Deflection to the

right in the

northern

hemisphere

Deflection to the

left in the southern

hemisphere

No deflection at

all at the equator

Maximum deflection at the poles

Maximum deflection at the poles

POINTS TO REMEMBER ABOUT THE

CORIOLIS FORCE:

1.It is an apparent force that works to deflect

air to the RIGHT in the northern hemisphere,

LEFT in the southern hemisphere.

2. It always acts at 90° to the wind direction.

3. It is directly proportional to wind speed.

4. It is directly proportional to latitude.

EFFECTS OF THE CORIOLIS

FORCE: GEOSTROPHIC WIND

Simple case: the absence of friction

HIGH

Geostrophic wind (no friction):

wind travels parallel to isobars,

without crossing them.

LOW

Northern hemisphere: wind deflected to the right

WINDS AT THE SURFACE

Importance of friction

1020 mb

1016 mb

1012 mb

1008 mb

HIGH

LOW

Pressure

gradient force

=

Coriolis force

Wind direction

HIGH LOW

Northern hemisphere: wind deflected to the right

Winds at the surface: wind crosses

isobars at an angle.

HIGH- CLOCKWISE LOW- COUNTER CLOCKWISE

0°

(equator)

30°N 90°N

(north pole) 60°N 30°S 90°S

(south

pole)

60°S

WARM COLD COLD

General circulation of the atmosphere- part II.

H H

Hadley cells

Subtropical high pressure cells

Polar front Polar front

JET

JET

JET

JET

H

L O W

Intertropical

Convergence

Zone (ITCZ)

Trade

winds

Mid-latitude

westerlies

The general circulation of the atmosphere.

Source: Christopherson, 2012, p. 142.

Global surface barometric pressure- January.

Source: Christopherson, 2012, p. 140.

Global surface barometric pressure- July.

Source: Christopherson, 2012, p. 140.

Stylized cross-

section of the polar

front jet.

Source: Christopherson, 2012, p. 147.

The Earth’s surface ocean currents.

Source: Christopherson, 2012, p. 153.

The Earth’s deep ocean currents (vertical circulation).

Source: Christopherson, 2012, p. 155.