Download The Atmosphere

The Atmosphere
Origin, Composition & Structure
Formation of the Solar System
• Our sun and the planets originated from a
solar nebula that had been enriched with
heavy elements from nearby super novae
• Solar system is approximately 5 Billion
years old
• Composition is 75% hydrogen, 23%
helium and 2% other materials
• 4 heavy terrestrial inner planets; 4 lighter
jovian outer planets
NEBULAR HYPOTHESIS
Nebula & Solar System
Earth
Evolution of the Atmosphere
• Primary Atmosphere
– Lost to space early on
• Secondary Atmosphere
– Recorded in the rocks
Origin of Atmosphere
• Atmosphere evolved in 4 steps:
– primordial gases, later lost due to sun's
radiation
– exhalations from the molten surface (volcanic
venting); bombardment from icy comets
– steady additions of carbon dioxide, water
vapor, carbon monoxide, nitrogen, hydrogen,
hydrogen chloride, ammonia, and methane
from volcanic activity
– addition of oxygen by plant/bacterial life
Volcanic Outgassing
Atmosphere & Oceans are
byproducts of heating and
differentiation: as earth
warmed and partially
melted, water locked in the
minerals as hydrogen and
oxygen was released and
carried to the surface by
volcanic venting activity
Vapor Outgassing from
Volcanic fumarole
Formation of the Atmosphere &
Oceans: Prevailing Theory
• The major trapped volatile was water (H2O). Others
included nitrogen (N2), the most abundant gas in the
atmosphere, carbon dioxide (CO2), and hydrochloric
acid (HCl), which was the source of the chloride in sea
salt (mostly NaCl).
• The volatiles were probably released early in the Earth's
history, when it melted and segregated into the core,
mantle, and crust. This segregation occurred because
of differences in density, the crust being the "lightest"
material.
• Volcanoes have released additional volatiles throughout
the Earth's history, but probably more during the early
years when the Earth was hotter.
• Probably, the oceans formed as soon as the Earth
cooled enough for water to become liquid, about 4 billion
years ago. The oldest rocks on the earth's surface today
are 3.96 billion years old.
ATMOSPHERE
• Present Composition
– 78% Nitrogen; 21% Oxygen; trace amounts of CO2, Argon,
ect.
• Atmosphere Unique Among Other Planets
– Venus & Mars CO2 Gaseous planets H, He, CH4
– Pressure in Venus 100x Earth on Mars 1/100
– Surface Temperature 450-500oC Venus; -130-25oC Mars
• Atmospheric Gases Controlled by volcanoes and
interactions between gases and the solid Earth &
Oceans as well as biotic component
• Ozone (O3): produced by photochemical Rx absorbs
harmful UV radiation
The Origin of the Atmosphere
• Primary Gases from Accretion
– rich in H, He, CH4
• Secondary Atmosphere
– Degassing of Earth by volcanic activity
• large number of volcanoes/volcanic rks
• Rich in Argon-40 (99.6%) as compared to Sun
(0.01%)
– 40Ar product of radioactive decay of 40K
Was there a Primary
Atmosphere?
• No evidence that one existed or if it did it was gone
soon after planetary accretion
• Primary Atmosphere then disappeared early as a
consequence of:
– Solar wind
– Formation of moon
Secondary Atmosphere
• Degassing- liberates CO2 and H2O vapor
– Outgassing of water occurred within first 1by
– volcanism
• Gases in near surface reservoirs are identical to volcanic
gases
– weathering
• Terrestrial atmosphere rich in CO2 and H2O by
4by
N2 retained in atmosphere, H2O vapor lost by
condensation to ocean; CO2 combined with Ca &
Mg to form carbonate Rks; H2 lost to space
Oxygen in the Atmosphere
• Earth only planet in solar system with oxygen
thus only planet able to sustain higher forms of
life
• Oxygen produced by
– Photosynthesis- algae and plants
– Photolysis-fragmentation of water molecules into
Hydrogen and Oxygen
• Oxygen consumed by
– Respiration
– Decay
– Weathering (chemical oxidation)
Oxygen in the Primitive
Atmosphere
• Photosynthesis NOT important prior to
advent of microorganisms (cyanobacteria);
only after 3.5 by
• Controlled by rate of Photolysis which was
controlled by the outgassing of water from
volcanoes, the rate of hydrogen escaping to
space and the losses from weathering
Geologic Indicators of Atmospheric
Oxygen Levels
•
•
•
•
Banded Iron Formations (BIFs)
Redbeds, Sulfates and Uraninite
Paleosols
Biological Indicators
Structure of the Atmosphere
• The atmosphere is a reasonably well-mixed envelope of
gases roughly 80 km (54 mi) thick called the
HOMOSPHERE.
• Above 80 Km the gases are stratified such that the
heavier gases decrease much more rapidly than the
lighter ones; this is the HETEROSPHERE
• In addition, we can identify four layers in the atmosphere
that have distinct characteristics.
• The four layers of the atmosphere, in order from lowest
to highest elevation, are:
–
–
–
–
the troposphere,
the stratosphere,
the mesosphere,
the thermosphere
The Troposphere
• The density of the atmosphere decreases rapidly
with increasing height.
• The troposphere has the following
characteristics:
– it is about 12 km (7 mi) thick,
– the temperature decreases rapidly with altitude,
– the mean temperatures at the bottom and top are
16°C & -60°C,
– it is heated from below by conduction and from
condensation of water vapor,
– it is the region where you find precipitation,
evaporation, rapid convection, the major wind
systems, and clouds, and
– it is the densest layer of the atmosphere.
The Tropopause/Stratosphere
• Above the troposphere is a region of relatively
constant temperature, -60°C, about 10 km (6 mi) thick
called the tropopause.
• This is where high velocity winds (jet streams) occur.
• The stratosphere has the following characteristics:
– it is about 28 km (17 mi) thick,
– the temperature increases with altitude from about -60°C to
0°C,
– this is where ozone, an unstable form of oxygen, appears,
– it is heated as the ozone absorbs incoming ultraviolet
radiation.
Stratosphere/Stratopause
• The stratosphere offers clear, smooth
conditions for flying
• No air exchange between it and
troposphere
• Gases and aerosols can persist for
months or years triggering short term
climatic variations
• A constant temperature condition is
described as isothermal
• The stratopause is at 0oC
Mesosphere/Mesopause/Thermosphere
• Mesosphere temperatures fall with
increasisng altitude until they reach the
Mesopause at 80Km and -95oC
• Above the mesopause is the
Thermosphere where temperatures are
isothermal for 10Km then rise rapidly with
increasing altitude
• The thermosphere is very sensitive to
incoming solar radiation
The Ionosphere
• From between 70 and 80Km in the
Thermosphere to an indefinite altitude in
the Thermosphere
• High concentration of ions of Oxygen and
Nitrogen
• Solar wind strips electrons from these
atoms and molecules
Ionosphere
Aurora Australis
NASA Images from Space
Measuring the Atmosphere:
Historical Perspective
• Rainfall measured in India using rain
gauges 400 BCE
• Aristotle’s Meteorologica (350-340 BCE)
• Galileo invented the thermoscope
(thermometer) 1592
• Torricelli invents mercury barometer 1643
Galileo & Torricelli
Monitoring the Atmosphere
Upper Air Observations
• A three-dimensional picture of temperature,
pressure, relative humidity, and wind speed and
direction in the atmosphere is essential for
weather forecasting and meteorological
research
• During the latter part of the 19th century and the
first quarter of the 20th century, this information
was obtained mainly by meteorographs sent
aloft on tethered kites, which automatically
recorded, on a single sheet, the measurements
of two or more meteorological parameters such
as air pressure, temperature, and humidity
Monitoring the Atmosphere
Kites & the Radiosonde
The Radiosonde
• The radiosonde is a small, expendable instrument
package that is suspended below a large balloon filled
with hydrogen or helium.
• The radiosonde consists of sensors coupled to a radio
transmitter and assembled in a lightweight box.
• The meteorological sensors sample the ambient
temperature, relative humidity, and pressure of the air
through which it rises.
• As the radiosonde is carried aloft, sensors on the
radiosonde measure profiles of pressure, temperature,
and humidity.
• These sensors are linked to a battery powered, 300
milliwatt radio transmitter that sends the sensor
measurements to a sensitive ground receiver.
Worldwide, there are more than 900 upper-air observation stations using 15 major types of radiosondes. Most
stations are located in the Northern Hemisphere and all observations are taken at the same times each day at
00:00 and 12:00 UTC (Greenwich Mean Time), 365 days per year. Observations are made by the NWS at 93
stations - 72 in the conterminous United States, 13 in Alaska, 10 in the Pacific, and 1 in Puerto Rico
The Radiosonde
• During the flight train's ascent, the radiosonde
continuously transmits temperature, relative humidity,
and pressure readings to the ground-based Radiosonde
Tracking System which is housed in a fiberglass dome
above the inflation shelter.
• Wind speed and direction are determined for each
minute of the flight, generally 90 minutes.
• They are determined from changes in the position and
direction of the flight train as detected by the Radiosonde
Tracking System.
• When winds are incorporated into the observation, it is
termed a rawinsonde observation, and all National
Weather Service upper air stations take rawinsonde
observations
Monitoring the Atmosphere
Those observations that reach the bursting
altitude of the regular 600-gram balloon attain an
average height slightly in excess of 90,000 feet.
The average bursting altitude for stations using
the larger 1,200-gram balloon exceeds 100,000
feet
Radiosonde
• Approximately one-third of the radiosondes
released by the National Weather Service are
found and returned to the Instrument
Reconditioning Branch in Kansas City, Missouri,
• They are repaired and reissued for further use,
some as many as seven times.
• Instructions printed on the radiosonde explain
the use of the instrument, state the approximate
height reached, and request the finder to mail
the radiosonde, postage free
Other Monitoring
• Radar
• Satellites