The Earth and Its Atmosphere
Atmosphere: the envelope of gases that surrounds a planet and
is held to it by the planet's gravitational attraction. The earth's atmosphere
is mainly composed of nitrogen and oxygen. Although our atmosphere extends
upward for many hundreds of kilometers, 99% of the atmosphere's mass is
confined within a 30 km of the earth's surface.
Weather: the condition of the atmosphere at any particular time
and location, defined as temperature, cloudiness, precipitation, and wind
speed and direction. Meteorology is the study of the atmosphere
and the processes that cause weather. A professional meteorologist is a
person who has completed the requirements for a college degree in meteorology
or atmopsheric science.
Figure 1.17, page #21 (Ahrens)
Climate: the representation of daily and seasonal weather events
over a long period of time. The distribution of the weather element throughout
the season or year, departures from long term averages, anomalies, and
extremes in weather are also important aspects of climate. Climate usually
employs the values of the weather elements at the earth's surface. For
example, the climate of Baltimore, Maryland is characterized by the annual
average precipitation of 41.8 in. and annual mean temperature of 55 F.
Climatology is the study of climate, its control and variability. A
climatologistis a person who stidues the interaction between land, ocean,
and the atmosphere and its influence on planet Earth many years from now.
Figure 17.7, page #480-481 (Ahrens)
The earth's atmosphere today is the result of a longtime evaluation
process that began billions years ago. The early atmosphere was likely composed of
hydrogen and helium. More dense atmopshere than today was the second stage due to
the escape of gases from Earth's interior in the presence of abudant carbon dioxide
Outgassing: the release of gases from hot, molten rock during volcanic activity. It was the
main source of atmospheric gases, which was mostly CO2, with some nitrogen (N2),
water vapor, and trace gases of methane, ammonia, sulfur dioxide, and
The decline in the atmospheric CO2 concentration was evident
as the planet cooled enough to condensate the water vapor into clouds
and rainfall. Carbon dioxide dissolves in rainwater and produces weak carbonic
acid that reacts chemically with the bedrock; large-scale geo-chemical process.
The formation of molecular oxygen (O2) probably began as energetic rays from the sun
split water vapor into hydrogen and oxygen during photodissociation. The
hydrogen is lighter and probably escaped to the space and the oxygen stayed in the
Photosynthesis: the product whereby plants use sunlight, water,
and CO2 to manufacture their food. It was the primary source of oxygen
(O2) and became an important component of the atmosphere's evaluation by about 2-3 billion
After the plants evolved, the atmospheric content increased rapidly and probably
reached its present composition about several hundred millions ago.
Breath of airthe volume of average size breath of air is one liter
(10^-3 m3). At sea level, there are roughly 10^22 air molecules in a liter and there
are nearly 10^44 molecules in the atmosphere.
Homosphere: the atmosphere up to 80 km (50 mi.) in which the
proportions of the principal gases, N2 (78%) and O2 (21%) remain relatively
constant. The homosphere also contains 1% of argon and small quantities
of permanent gases of helium, neon, hydrogen, and xenon and variable gases
of water vapor, CO2 (0.035%), methane, nitrous oxide, and ozone (O3) and
particles of dust, aerosols, cloud droplets and ice crystals.
The significance of an atmospheric gas or aerosol is not necessarily
related to its relative concentration. Water vapor, CO2, and O3 are minor
in concentration but are extremely important in atmospheric radiative processes.
Water vapor is the main source of water around the globe; CO2 is essential
for photosynthesis; O3 protects live organisms from ultraviolet radiation
of the sun.
Table 1.1, page #6 (Ahrens)
Heterosphere: the atmosphere above 80 km in which gases are stratified
such that concentrations of the heavier gases decrease more rapidly than
do concentrations of lighter gases. Within the heterosphere, above about
150 km, oxygen is the major atmospheric gas but it occurs primarily in
the atomic (O) rather than diatomic (O2) form. Ultraviolet radiation from
the sun photo-dissociates O2 into its constituent atoms.
the breakdown of molecules by radiation. Because of low air density
at these altitudes, the collision of two oxygen atoms into a molecule is
infrequent. At lower altitudes, below 100 km, the rate of recombination
of oxygen atoms exceeds the rate of photo-dissociation of oxygen molecules.
Exosphere:the upper limit of the atmoshere. It is the region where atoms and molecules shoot off
Aerosols: tiny liquid or solid particles that occur suspended in the
atmosphere. They originate through forest fires, as sea-salt crystals from
ocean spray, from wind erosion of soil, in volcanic emissions, from industrial
and agricultural activities. Some aerosols act as nuclei for the development of
clouds, and precipitation, and have some influence on air temperature by
interacting with solar radiation.
Air pollutant: a gas or aerosol substance that occurs in concentrations
high enough to threaten human health, to disrupt physical and biological
processes, or to toxify a given environment. The concentration of a gaseous
pollutant is expressed as number of pollutant molecules per million molecules
of air (parts per million, ppm), while aerosol concentration are given
in mass of pollutant per unit volume of air (micrograms per cubic meter).
Acid rain:cloud droplets or raindrops combining with gaseous
pollutants (e.g. SO2, NOx) to make rain acidic - pH less than 5.0. If the fog
droplets combine with such pollutants, it becomes acid fog
Figure 19.24, page 559 (Ahrens)
Figure 19.25, page 560 (Ahrens)
Air pollutants are produced by natural events and human activities,
anthropogenic. Natural sources of air pollutants include forest
fires, pollen dispersal, soil erosion, volcanic eruptions, and decay of
dead plants and animals. Anthropogenic sources of air pollutants include
emissions from automobiles, oil refineries, chemical plants, etc.
Air pollutants are classified according to two categories: Primary
air pollutants are those directly emitted into the air. The most important
primary air pollutans are particulate matter, sulfur oxides, carbon monoxide,
hydrocarbons, and nitrogen oxides.
Primary air pollutants can undergo chemical reactions within the atmosphere
and produce new substances known as secondary air pollutants. The
photochemical smog and ozone are the most important secondary air pollutants.
Both are generated as a result of interaction between the intense sunlight
and the primary pollutans. Smog is the combination of fog and smoke.
The Martian atmosphere consists of mainly CO2 (95%), N2, argon, and
O2. It is much thinner; its surface pressure is only 0.7% of the Earth's
average sea-level pressure (1013.25 mb). Volcanic eruptions are the primary
source of gases of the Martian atmosphere.
The average surface temperature is about -60 C (-76 F). Water in unknown
quantities mixed with solid CO2 (dry ice) exists in the polar ice caps
and scattered patches of permafrost. There are no photosynthesis, and hence,
no free oxygen in the Martian atmosphere.
Gravity is about 38% of the Earth. This is because Mars
is smaller, 53% of the Earth's equatorial diameter (1.274x107
m) and is less massive, 10% of the Earth's mass (5.98x1024 kg).
The Venusian atmosphere consits of mainly CO2 (95%), N2, and water vapor. The atmopshere
is thick through opaque acid cloud deck. The surface pressure is 90,000 millibars, which
is 90 times greater than the Earth.
The average surface temperature is 480 C (900 F). It is slightly smaller than the Earth.
The outer planets (Jupiter, Saturn, Uranus, Neptune) are greater than the Earth in our solar system.
The Jupiter and Saturn are composed of H2 and He. Among the other plantes,
Uranus are composted of methane and H2, while Neptune has mainly methane and N2. In terms of
density, the inner plantes (Mercury, Venus, Earth, Mars) are denser than the outer plantes
Figure 1.2, page #5 (Ahrens)
Table 1, page #14 (Ahrens)
Through the early part of the twentieth century, weather intruments
borne by kites, aircraft, and balloons provided information about the lowest
5000 m of the atmosphere followed by rockets, radiosondes, satellites,
Radiosonde: the instrument that consists of an instrument package
and radio transmitter carried by balloon to altitudes of about 30 km (19
mi.) It provides vertical profiles (soundings) of temperature, pressure,
and relative humidity. The pressure, humidity, and temperature are measured by
separate sensors attached to the box and transmited by radio. A tracking instrument
with global positioning system provides the vertical profile of wind. It is launched
twice a day corresponding noon and midnight at universal time.
Figure 4, page #16 (Ahrens)
Dropwindsonde: another instrument similar to radiosonde but it
is dropped from an aircraft and descends on a parachute at about 18 km
(11mi.) per hour. It provides vertical profiles of air temperature, pressure,
humidity, and wind. Dropwindsondes were developed to obtain soundings over
Surface launched rockets that provided information at altitudes of 110
to 165 km was replaced by satellites which monitor patterns of temperature
and water vapor concentration, upper-air winds, and the life cycles of
severe storms. Radar, on the other hand, determines the location and movement
and intensity of precipitation.
Based on the average vertical temperature profile, the atmosphere is
subdivided into four concentric layers, troposphere, stratosphere, mesosphere,
and thermosphere. Almost all weather takes place in the troposphere and
Troposphere: the lowest thermal layer that extends from the earth's
surface to an average altitude ranging from about 6 km at the poles to
about 16 kilometer at the equator. The temperature within the troposphere
usually, but not always, decreases with height with a rate of 6.5 ûC
per 1000 meters. Tropopause is the transition zone between the troposphere
and the stratosphere.
Stratosphere: the thermal layer that extends from the tropopause
up to 50 km. The temperature within the stratosphere is constant, isothermal,
below about 20 km and increases with height above about 20 km at which
ozone concentration reaches its maximum. It is the ideal layer for jet
aircraft travel since it is above the weather. Stratopause is the
transition zone between the stratosphere and the mesosphere.
Mesosphere: the thermal layer that extends from the stratopause
up to 80 km. The temperature within the mesosphere decreases with height
reaching its lowest average value of -95 C (-139 F). Mesopause is
the transition zone between the mesosphere and thermosphere.
Thermosphere: the outmost thermal layer that extends from the
mesopause outward to space. The temperature within the thermosphere is
at first isothermal and then rise rapidly with height. It is the region
in which sun dissociates oxygen and nitrogen and ionizes the atmospheric
Figure 1.11, page #13 (Ahrens)
Ionosphere: the region within the thermosphere, between altitudes
of 80 to 400 km, that contains relatively high concentration of ions, electrically
charged particles. Within the ionosphere, the charged subatomic particles
reflect outgoing radio waves. Multiple reflections between the ionosphere
and the Earth's surface greatly extend the range of radio transmissions.
The relatively good reception of distant radio signals at night results
from the reflection of radio waves by the upper ionosphere.>
Based on electron density, the ionosphere is subdivided into three layers:
D-layer (60 to 90 km), E-layer (90 to 140 km), and F-layer (above 140 km).
Since electron density increases nearly continuously with altitude to a
maximum at an average level close to 300 km, D- E-, and F-layers are not
discrete, rather differ each other on the reflection of radio waves.
Figure 1.13, page #16 (Ahrens)
The production rate of ions and electrons depends on i) the density
of atoms and molecules for ionization, which decreases with height, ii)
the intensity of solar radiation which increases with height.
Aurora borealis (northern lights): greenish-white lights produced
by electrical activity in the ionosphere. They are visible at night in
the Northern Hemisphere at altitudes between 100 and 400 km.
Aurora australis (southern lights): greenish-white lights produced
by electrical activity in the ionosphere. They are visible at night in
the Southern Hemisphere at altitudes between 100 and 400 km.
Each atmospheric gages has its own sets of energy levels, therefore its own
charactersitic color. The molecular nitrogen gives off violet and red, while atomic
oxygen can emit red or green.
Figure 2.22, page #53 (Ahrens)
Auroral ovals: the geographic areas where the aurora is visible.
They are situated between 20û and 30û of latitude from the
geomagnetic poles. In the Northern Hemisphere, they are centered on the
northwest tip of Greenland.
Figure 2.23, page #54 (Ahrens)
Auroral activity varies with the sun's activity. When the sun is quiet,
the auroral oval shrinks, but when the sun is active, the auroral oval
expands equatorward, and the aurora may be visible across southern Canada
and northern United States, or rarely, even further south. The sun's activity peaks
about every 11-year.
Solar flares: the gigantic disturbances on the sun that emit
the high-velocity streams of electrically charged subatomic particles to
space. They last perhaps an hour and produce a shock wave that propagates
rapidly 500 to 1000 km/sec through the solar wind.
Magnetosphere: the region within the ionosphere in which solar
wind is deflected by the Earth's magnetic field and is deformed into a
teardrop-shaped cavity surrounding the planet. An aurora results from the
interaction between the solar wind and the Earth's magnetic field. On the side
facing to the sun, the pressure of the solar wind compresses the field lines. On the
opposite site, the magnetosphere stretches out into a long tail -
magnetotail- which reaches far beyond the moon's orbit.
Solar wind: a stream of electrically charged subatomic particles
(protons and electrons) that continually emanates from the sun and travels
into space at speeds of 400 to 500 km/sec.
Bow shock:a boundary at which the speed of solar wind abruptly
drops as a results of its approach to the magnestosphere.
Figure 2.20, page #51 (Ahrens)
Airglow:light from ionized oxygen and nitrogen and other gases that have been excited by solar
radiation. It is a faint glow at night, much weaker then the aurora, no correlation
with solar activity.