Ocean and Atmospheric Circulation

Susan Howard Earth & Space Research

Basically – why and how the ocean and atmosphere MOVE!

www.ametsoc.org 

There are many scales of motion: From BIG to very small

Today – I will just cover the basic large scale, GLOBAL circulation.

The Ocean and Atmosphere are in CONSTANT motion

NASA/Goddard Space Flight Center Scientific Visualization Studio

NASA Movie: Perpetual Ocean

Model of ocean currents based on data from satellites and other measurements.

There are 2 main things that form the Global Ocean and Atmospheric circulation patterns

set up the climate system we know it.

• Energy from the Sun

• Rotation of the earthWarming from the sun Sets it in Motion

The rotation directs the motion

Energy and the Sun

The Sun is constantly emitting energy, in the form of “electrogmagnetic radiation”.

What is ELECTROMAGNETIC RADIATION?

• Light• Infrared (Heat)• Xrays• Microwaves• Ultraviolet radiation (sunburns!)

Solar radiation travels through space and hits the earth and warms it.

The Heating of the Earth is Not Even!

Short length of day

Small angle of incidence/ low intensity Large amounts of Ice cover

Noon in Antarctica May

23rd, 2001

UNEVEN HEATING: The daily amount of warming at a point on the Earth depends on 3 things

The Heating of the Earth is Not Even!

• Length of Day - How much sunlight a point receives in a day

• Angle of Incidence (Intensity) – the angle of the sunlight that reaches the earth

• Albedo – how much of this light is reflected.

Length of Day

• Earth is tilted with respect to Sun• Length of day changes throughout the year

Source: Wikipedia

NH Summer

NH Winter

Length of Day

Source: Wikipedia

Equinox

Solstice

Angle of Incidence

A beam of light shining straight down is more intense that a beam of light shining at an angle

The angle the incoming light makes with respect to the Earth

Angle of incidence

Wikipedia

Intensity of Radiation Varies with Latitude

The further you get from equator, the less radiation reaches the earth per area

Source: http://atschool.eduweb.co.uk/kingworc/departments/geography/nottingham/atmosphere/pages/solarradiationalevel.html

Because the Polar regions receive less radiation, they are cooler.Because they are cooler – ice forms.

It reflects the solar radiation

What does Sea Ice do?

High albedo – high reflectionLow albedo – high absorption

Ice cover – reflects radiation

Radiation reflected

Radiation absorbed

Warms water

So Ice makes the polar regions even cooler!

So, because of angle of incidence, length of day, & ice:

Equator

Pole

The Equator gets more heat than the Poles ...

a lot more!

Warmer Cooler

Average Annual Heating by Sun

Source: Wikipedia

Ocean temperature movieFrom NOAA, Based on satellite measurements

What does this Uneven Heating do?

• Hot air and cold air behave differently

Hot air risesCold air will sink.

• And this causes MOTION

Warm air rises

Cold air sinks

How Wind Forms

Low Pressure

HighPressure

Wind

Wind

Convection Cell

****Air likes to go from areas of High pressure to Low pressure

The GLOBAL Air Circulation is controlled by these convection cells

Figure 7.5 in The Atmosphere, 8th edition, Lutgens and Tarbuck, 8th edition, 2001.

So, we know:

1)The SUN heats the earth UNEVENLY – And this is going to cause motion.a. The uneven heating causes the rising and sinking

of airb. And this rising and sinking causes WIND.c. The sun has set the atmosphere in motion

2) What going to now DIRECT this motion ?

ROTATION of the Earth

2) Rotation of the Earth it helps DIRECT the circulation.

It works at right angles to motion and makes the motion curve

Coriolis Force

Equator

Right in Northern Hemisphere

Left in Southern Hemisphere

Coriolis Force

Global Wind Patterns

No Rotation

With Rotation

http://www.srh.noaa.gov/jetstream/global/circ.htm

Global wind patterns based on Solar heating and Rotation

Early Explorers relied on the global wind patterns to sail around the world

Summary Movie – Air circulation

Movie : Global Atmospheric Circulation By Keith Meldahl, YouTube video

Sun’s Heating and Earth’s rotation create wind circulation patterns

creates Global Surface Currents in Ocean

Wind motion creates Surface Currents in Ocean

Map of basic surface currents

http://oceanmotion.org/html/background/wind-driven-surface.htm

Wind AND ocean currents

http://staff.orecity.k12.or.us/steve.tebor/atm%20currents/current/images/world_circulation.jpg

Because of uneven heating, just like the Atmosphere, the ocean also has Convection Cells which drives DEEP circulation

The Wind drives large scale surface currents but that isn’t all.

Basic facts

Warm WATER rises Cold WATER sinks

Warm air rises Cold air sinks

Ocean Conveyer Belt

Ocean circulation – major currents

Movie : GFDL Ocean current move

Questions?