Formationof the

Atmosphere

‣ Most of the Earth’s early atmosphere was lost due to the vigorous solar wind from the early Sun.

‣ Continuous volcanic eruptions built a new atmosphere of:

water vapor

carbon dioxide

nitrogen

methane

Formation of the Atmosphere

‣ Comets brought water and organic molecules.

‣ Oxygen did not appear in the atmosphere until after the first bacteria evolved.

Early plants released oxygen as a waste product

and helped to build the atmosphere.

Once oxygen was present in the atmosphere,

ozone could form, blocking out the Sun’s ultraviolet

rays and changing the way life evolved.

The Atmosphere

‣Earth's atmosphere contains roughly:

The Earth’s atmosphere (where pressure becomes negligible) is over 140 km thick. Compared to the bulk of the planet, this is an extremely thin barrier between the

hospitable and the inhospitable.

78% nitrogen

20.95% oxygen

0.93% argon

0.038% carbon dioxide

Trace gases

1% water vapour

All images: NASA

The Atmosphere

‣ The mixture of gases known as air, protects life on Earth by absorbing ultraviolet radiation and reducing temperature extremes between day and night.

‣ The atmosphere is not static. Interactions involving the amount of sunlight, the spin of the planet and tilt of the Earth’s axis cause ever changing atmospheric conditions.

The auroras occur in the thermosphere and are caused by interactions between the Earth’s atmosphere and charged particles streaming from the Sun.

Weather occurs in the troposphere. Gaseous water molecules held together by intermolecular forces cause the formation of clouds.

Atmospheric Layers

‣ The atmosphere consists of

layers around the Earth,

each one defined by the way

temperature changes within

its limits.

‣ The layer boundaries are:

Tropopause

Stratopause

Mesopause

‣ The outermost, the

thermosphere, thins slowly,

fading into space with no

boundary.

TroposphereAir mixes vertically andhorizontally. All weatheroccurs in this layer.

StratosphereTemperature is stable to20 km, then increases due to absorption of UV by the thin layer of ozone.

MesosphereTemperature is constant in the lower mesosphere, but decreases steadily with height above 56 km.

ThermosphereThis layer extends as high as 1000 km. Temperature increases rapidly after about 88 km.

Aurora, caused by collisions between protons and electrons from the Sun and oxygen and nitrogen atoms in the atmosphere.

Meteor burning up

Movement of Air

‣ The air of the atmosphere moves in response to heating from the Sun.

‣Circulation in the atmosphere transports warmth from equatorial areas to high latitudes, returning cooler air to the tropics.

‣ The rotation of the Earth causes these movements to break up into three distinct air cells in each hemisphere.

Westerlies

Westerlies

High

High

Southeasterly trade winds

Northeasterly trade winds

Equator

Polar cell

Polar cell

cell

cell

Ferre

l

Ferrel

Hadley

cell

Had

ley

cell

Image NASA

Air CellsRising mid-latitude air divides, flowing to the poles and the equator forming the Ferrel cells. These mid-latitudinal cells produce westerly winds.

In the tropics, wind blowing towards the equator as part of the Hadley cells is deflected (by the Coriolis effect) and forms the northeasterly and southeasterly trade winds.

Air within the Hadley cells rises moist at the equator and subsides dry at the tropics.

60o N

30o N

0o

Polar cell

Hadley

cell

Ferrel

cell

EquatorImage NASA

Air Cells0o

30o S

60o S

The atmospheric circulation in each hemisphere consists of three cells (at polar, mid-latitude, and equatorial regions). These cells produce belts of prevailing winds around the world.

Warm air rises at the equator and moves poleward through the upper troposphere before sinking at the edge of the tropics.

At the poles, air cools and descends as a cold, dry high pressure area, moving away from the pole flowing towards the equator.

EquatorImage NASA

Coriolis Effect

‣ Energy from the Sun is distributed through a global system of atmospheric and ocean circulation that creates the Earth's climate.

‣ Heated air moving towards the poles from the equator does not flow in a single uniform convection current.

‣ Friction, drag, and momentum cause air close to the Earth's surface to be pulled in the direction of the Earth's rotation.

Air flowing towards, or away from, the equator follows a curved path that swings it to the right in the northern hemisphere and to the left in the southern hemisphere. This phenomenon, known as the Coriolis effect, is caused by the anticlockwise rotation of the Earth about its axis.

Image: NASA

Coriolis Effect

‣ The deflection of moving air is called the Coriolis effect and it is responsible for the direction of movement of large-scale weather systems in both hemispheres.

‣ Air flows from high pressure to low pressure.

In the northern hemisphere, cyclonic (low pressure) systems rotate counterclockwise.

In the southern hemisphere, cyclonic systems spiral in a clockwise direction.

‣ Cyclonic weather is usually dull, with cloud and persistent rain.

Cyclone, Southern hemisphere

Hurricane, Northern hemisphere

All photos NASA

The Ocean Surface

‣ Throughout the oceans, there is a constant

circulation of water, both across the surface

and at depth.

‣ Surface circulation, much of which is in the

form of circular gyres, is driven by winds.

‣ The polar oceans comprise the Arctic Ocean

in the northern hemisphere and the Southern

Ocean in the south. They differ from other

oceans in having vast amounts of ice, in

various forms, floating in them.

‣ This ice coverage has an important

stabilizing effect on global climate, insulating

large areas of the oceans from solar radiation

in summer and preventing heat loss in winter.

The Southern Ocean encircles Antarctica and is covered in ice for much of the year. Complex currents in the Southern Ocean produce rich upwelling zones that support abundant plankton and complex food webs.

Satellite observations have shown the sea ice around the poles is melting earlier and more rapidly than first thought. The loss of ice dramatically reduces the albedo (reflectivity) of the polar regions.

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Ocean Currents‣ The deep-water ocean currents (the thermohaline circulation) is driven by the

cooling and sinking of water masses in polar and subpolar regions.

‣ Cold water circulates through the Atlantic, penetrating the Indian and Pacific

oceans, before returning as warm upper ocean currents to the South Atlantic.

‣ Deep water currents move slowly and once a body of water sinks it may spend

hundreds of years away from the surface.

Pacific Ocean

Warm shallow current

Atlantic Ocean

IndianOcean

Cold and deep high salinity current

High salinity water cools and sinks in the North Atlantic.

Atlantic waters are saltier and therefore more dense than those in the Pacific.

Cold water circulates through the Atlantic penetrating the Indian and Pacific Oceans.

The polar oceans (the Arctic and Southern Oceans) are sources of cold dense bodies of water that drive the Earth’s deep water circulation.

Deep water returns to the surface in the Pacific and Indian oceans through upwelling.

Gyres‣ The movement of surface waters tends to form ocean-wide vortices.

‣ At the center of these vortices, water currents are almost nonexistent and water tends to be stagnant.

‣ The Sargasso Sea is a well known example.

North Pacific Gyre

South Atlantic GyreIndian Ocean Gyre

North Atlantic Gyre

South Pacific Gyre

Sargasso Sea

Great Pacific Garbage Patch

Great Pacific Garbage Patch‣ As with all vortices, debris is swept towards the middle of the water

currents.

‣ The Great Pacific Garbage Patch is an accumulation of plastic and other debris in the middle of the North Pacific Gyre.

‣ It spans an area of approximately 1.2 million km2.

Nearly two million Laysan albatrosses live on Midway. It is estimated all of them contain some quantity of plastic. This juvenile died after swallowing at least three bottle caps, some fishing line and a felt tip pen.

Midway Is.

Midway Island lies near the center of the GPGP. Every tide brings in vast amounts of debris, from parts of old fishing nets to plastic bags and bottles. It is a poignant example of how even the most isolated places of Earth are affected by human activities.

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