Review Question 1When is the subsolar point directly over 20°N latitude?

A) Never

B) Between the summer solstice and the fall equinox

C) Between the spring equinox and the summer solstice

D) B and C

Review Question 2Why is Pluto no longer considered a planet?

A) Because it is square

B) Because it is a thermonuclear reactor

C) Because it shares its orbit with another planet

D) Because it is 3 billion light years from the sun

Chapter 3Earth’s Modern Atmosphere

Geosystems 6eAn Introduction to Physical Geography

Robert W. ChristophersonCharles E. Thomsen

The AtmosphereAtmosphereAtmosphere: an envelop of gaseous mixture (also containing suspended solid and liquid particles and clouds) that encircles a planet

Earth’s Modern Atmosphere

The atmosphere is absolutely essential for life on Earth

Earth’s atmosphere exists in a series of spheres or layers that grade into one another  

Composition, temperature, and function  

Atmospheric Profile  Our atmosphere extends to roughly 32,000 km (20,000 mi) from surface

The top of the atmosphere has no clear boundary

Gravity holds our atmosphere in place

Top of Thermosphere is at 480 km (300 mi) = top of the principle atmosphere

Exosphere

Atmospheric Composition

Two broad regions:Heterosphere – outer atmosphere

80 km (50 mi) outwards, to top of thermosphere Layers of gases sorted by gravity

Homosphere – inner atmosphere Surface to 80 km (50 mi)Gases evenly blendedOzone layer

Atmospheric Pressure

Figure 3.3

Atmospheric Temperature

TroposphereSurface to 18 km (11 mi)

90% mass of atmosphere

Normal lapse rate – average cooling at rate of 6.4 C °/ km (3.5 F°/1000 ft)

Tropopause

Atmospheric Temperature

Temperature Profile

Figure 3.5

Atmospheric Temperature

Stratosphere18 to 50 km (11 to 31 mi)

Temperatures increase with altitude

Ozone layer

Stratopause

Atmospheric Temperature

MesosphereTemperatures decrease with altitude

Mesopause

Atmospheric Temperature

ThermosphereRoughly same as heterosphere

80 km (50 mi) outwards

Altitude of thermopause varies

Temperatures increase with altitude, but little actual heat

Atmospheric Function

IonosphereAbsorbs cosmic rays, gamma rays, X-rays, some UV rays

OzonospherePart of stratosphere

Ozone (O3) absorbs UV energy and converts it to heat energy

Protective Atmosphere

Figure 3.6

Four Principal Components of AtmosphereNitrogen from volcanic sources

Oxygen from photosynthesis

Argon through radioactive decay of isotopes

Carbon dioxide byproduct of life processes

Composition of the AtmosphereComposition of the Atmosphere

Atmospheric gasesAtmospheric gases

Permanent gasesPermanent gases Variable gasesVariable gases

Nitrogen (~78% of vol.)

Oxygen (~21% of vol.)

Argon (~1% of vol.)

…

Water vapor (0-4% of vol.)

Carbon dioxide (0.037% of vol.)

Ozone (0.000007% of vol.)

Methane (0.00017% of vol.)

...

Water VaporWater Vapor

The most abundant variable gas (0.25% of total atmospheric

mass).

Added and removed from the atmosphere through the

hydrologic cycle.

A major contributor to Earth’s energy balance and many

important atmospheric processes.

Carbon DioxideCarbon Dioxide

A trace gas accounting for only 0.037% of the atmosphere.

Added to the atmosphere through biologic respiration and

decay, volcanic eruptions, and natural and human-related

combustion.

Anthropogenically related increases in recent decades have

led to great concern with regard to global “greenhouse

warming”.

Removed from the atmosphere by photosynthesis (go to

biosphere).

Carbon DioxideCarbon Dioxide

The steady increase of atmospheric CO2.

Question: the seasonal variation?the seasonal variation?

MethaneMethane

1.7 ppm; increase 0.01 ppm/yr.

An extremely effective

absorber of thermal

radiation emitted by

Earth’s surface; hence

related in the warming of

the atmosphere.

Released to the atmosphere through fossil fuel activities,

livestock digestion, and agriculture cultivation (especially rice).

CarbonCarbon Sequestration – removing carbon in the form of carbon dioxide from the atmosphere and storing it in the terrestrial biosphere

Carbon stored in biomass of plants

Soil organic carbon is carbon retained by the soil in humus form

The Carbon Cycle- source of atmospheric

carbon dioxideHuman acitivities release 7.1 GtC/yr (gigatons of Carbon per year).2 GtC/yr absorbed by oceans.1.9 GtC unaccounted for.3.2 GtC remain in atmosphere.

Carbon BanksCarbon bank – program that enables organizations to keep track of a stock or supply of greenhouse gases in secure fashion for future use in the trading market

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