Earth’s Atmosphere: A Basic Intro

Earth’s Atmosphere:A Brief Intro

(and Ocean Circulation Patterns)

Dr. Mark A. McGinleyHonors College and Department of Biological

SciencesTexas Tech University

Atmosphere

• An atmosphere is a layer of gases that may surround a material body of sufficient mass and that is held in place by the gravity of the body.

• An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low.

• Some planets consist mainly of various gases, but only their outer layer is their atmosphere

• Wikipedia

Earth’s Atmosphere

Earth’s Atmosphere

• The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity.

• The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space.

The Earth’s Atmosphere

– The atmosphere has a mass of about 5×1018 kg• three quarters of which is within about 11 km (6.8 mi;

36,000 ft) of the surface.

– An altitude of 120 km (75 mi) is where atmospheric effects become noticeable during atmospheric reentry of spacecraft.

– The Kármán line, at 100 km (62 mi), also is often regarded as the boundary between atmosphere and outer space.

The Earth’s Atmosphere

The Layers of Earth’s Atmosphere

• We will talk about the layers of earth’s atmosphere in more detail later on.

• The layer closest to the earth is known as the troposphere– We live in the troposphere– Factors that affect climate and weather occur in

the troposphere

Composition of dry atmosphere, by volume[2]

ppmv: parts per million by volume (note: volume fraction is equal to mole fraction for ideal gas only, see volume (thermodynamics))

Gas Volume

Nitrogen (N2) 780,840 ppmv (78.084%)

Oxygen (O2) 209,460 ppmv (20.946%)

Argon (Ar) 9,340 ppmv (0.9340%)

Carbon dioxide (CO2) 394.45 ppmv (0.039445%)

Neon (Ne) 18.18 ppmv (0.001818%)

Helium (He) 5.24 ppmv (0.000524%)

Methane (CH4) 1.79 ppmv (0.000179%)

Krypton (Kr) 1.14 ppmv (0.000114%)

Hydrogen (H2) 0.55 ppmv (0.000055%)

Nitrous oxide (N2O) 0.325 ppmv (0.0000325%)

Carbon monoxide (CO) 0.1 ppmv (0.00001%)

Xenon (Xe) 0.09 ppmv (9×10−6%) (0.000009%)

Ozone (O3) 0.0 to 0.07 ppmv (0 to 7×10−6%)

Nitrogen dioxide (NO2) 0.02 ppmv (2×10−6%) (0.000002%)

Iodine (I2) 0.01 ppmv (1×10−6%) (0.000001%)

Ammonia (NH3) trace

Not included in above dry atmosphere:

Water vapor (H2O) ~0.40% over full atmosphere, typically 1%-4% at surface

Gases of the Atmosphere

• Nitrogen gas is the most common gas in the atmosphere– N2

– Two atoms of Nitrogen held together by a triple bond• Second strongest bond in nature (I think)

• Thus, nitrogen gas is fairly non-reactive– We are surrounded by Nitrogen, but we can not use

atmospheric nitrogen to help make proteins, nucleic acids, etc.

Gases of the Atmosphere

• Oxygen gas is the second most common gas in the atmosphere. O2

• Oxygen is required for aerobic respiration– Break down sugar to release energy that can be used by

our bodies• This process is much more efficient in the the presence of

oxygen

• O2 can be converted to O3 (ozone) in the atmosphere– We will talk about the importance of ozone later on

Gases of the Atmosphere

• Carbon dioxide (CO2)• Terrestrial plants convert carbon dioxide into

sugar during the process of photosynthesis– Energy stored in sugar is required to power most

life on earth• Carbon dioxide is a “greenhouse gas”

Wind

• Wind can be defined simply as air in motion. This motion can be in any direction, but in most cases the horizontal component of wind flow greatly exceeds the flow that occurs vertically.

• Wind develops as a result of spatial differences in atmospheric pressure. Generally, these differences occur because of uneven absorption of solar radiation at the Earth's surface.

Wind

Unequal Distribution of Solar Energy Across the Earth

• Solar radiation more concentrated at the equator than at the poles– Because of the curvature

of the earth

• Thus, warmer near the equator than at the poles

Effect of Increasing Temperature on Gasses

• When gasses are heated the molecules start to “move” more which results in a lower density of gas molecules– Fewer molecules per volume

• As the density decreases, the mass of the gas decreases

Hot Air Rises

• As air warms its density decreases which causes the warmer air to become lighter than the cooler air surrounding it

• Thus, the more dense, cooler air replaces the warmer, lighter air near the surface of the ground

• HOT AIR RISES

Hadley Cells

Hadley Cells

• Warm air at the equator rises and is replaced by cooler air moving from higher latitudes– From North to South in Northern Hemisphere– From South to North in the Southern Hemisphere

• As air rises it cools.– In the Northern Hemisphere high altitude winds

blow from South to North – In the Southern Hemisphere high altitude winds

blow from North to South

Hadley Cells

• As the air cools at high altitudes it becomes heavier

• Falls to the earth at approximately 30o latitude N and S

Importance of Hadley Cells

• Influence global wind patterns• Also have profound effects of global patterns

of precipitation– We will talk much more about this later on