ELEMENTS OF OCEANOGRAPHY

 

TOPIC 6 - THE EARTH'S ATMOSPHERE AND HEAT BUDGET [Lecture ppt | pdf]

Overheads - 1st Lecture

Characteristics of the Earth's Atmosphere
The atmosphere is composed primarily of gases, mostly of nitrogen(78%) and oxygen (21%)
The atmosphere behaves physically like a fluid
The atmosphere is more the 200km thick
More then half the mass of the atmosphere lies below 6km altitude
There are also trace amounts of other gases, including carbon dioxide and water vapor, and aersols (small solid particles)


Atmospheric structure
Troposphere (~0-15 km)
­ Closest layer to the earth's surface
­ Layer in which most weather occurs
­ Temperature and pressure decrease with altitude
Stratosphere (~15 - 50 km)
­ Contains the Ozone layer
­ Temperature increases with altitude
Mesosphere (~50-100 km)
Thermosphere (>100 km) = Ionosphere


Global Heat Budget
The primary source of heat energy to drive the global climate engine (atmospheric and oceanic circulation are critical components) is solar insolation (short wavelength radiation)
This input energy must be balanced by energy (long-wavelength radiation) leaving Earth or the Earth continue to heat up
Part of the heat budget is stored in the atmosphere - this sets the overall atmospheric temperature


Global Change Issues - Global Depletion
The ozone (O3) layer occurs in the upper stratosphere
Ozone absorbs the shortest wavelength (ultraviolet) solar radiation - without ths layer, cancer rates would skyrocket
Ozone ids formed by photodissociation of O2 near the equator and is carried toward the poles by stratospheric winds
Ozone naturally breaks down into O2 in a few weeks and needs to be replenished with equatorial O3
Recent studies note anomalous depletion of ozone near the poles (an locally to 45* latitude) during local winter
Depletion is linked to presence of fluorine - most likely source is man made chlorofluorocarbon gas used in refrigerators and spray cans

Global Change Issues - Greenhouse Effect I
Greenhouses are mostly made of glass
Glass is transparent to short wave-length (solar) radiation (lets it pass through)
Glass is almost opaque to long-wavelength radiation (reflects it back into green house)
Solar radiation enters greenhouse and heats up plants and other hard surfaces
Suraces re-radiate heat as long-wavelength (infrared) radiation but glass will not let this radiation escape
The result is greenhouse atmosphere gets hotter


Global Change Issues - Greenhouse Effect II
Certain gases (such as carbon dioxide, methane, and water vapor) behave like glass in the Earth's atmosphere and are called greenhouse gases
Human activities since the 19th century (beginning of Industrial Revolution) have dramatically increased carbon dioxide levels in atmosphere
Concern is that this will cause global warming of atmosphere
One problem is that we do not understand the Earth's climate system well enough to predict what will really happen

Overheads - 2nd Lecture

Forces Influencing Global Atmospheric Circulation
Atmospheric Heating
­ Solar insulation is the primary source of energy
­ Most heat input occurs near the equator and least input occurs at poles
­ Simple hemispheric convection results
Coriolis effect
­ Fluids in motion are affected by Earth's rotation
­ Causes air mases to move toward the right (left) n the northern (southern) hemisphere producing clockwise (counter-clockwise) eddies or cyclones


General Circulation Model
Effects of heating and rotation create three latitudinal zones of prevailing winds in each hemisphere
­ Trades (0*-30*), Westerlies (30*-60*), Polar Eastrlies (60*-90*)
­ Regions of no prevailing winds (Doldrums) occur at boundaries
­ At equator, rising water-laden air creates low pressure and Tropical storms.
­ At 30*, descending dry air creates high pressure and deserts
­ At 60* convergence of cold and warm air creates polar fronts and storms
­ Tropical zone circulation - Hadley cell; mid latitude circulation - Ferrell Cell

 

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