JnU

Jagannath University was opened in 20th october 2005.
It's 6th anniversary was held on 20th october 2011

Climatology, origin of atmosphere, structure, and composition of atmosphere

Origin Of Atmosphere:
Atmosphere is a thin layer
of gases surrounding our
planet. Many of the planets
in this solar system have
atmospheres, but none that
we know of have an
atmosphere quite like ours -
one that can support life.
The Earth's primitive
atmosphere was much
different from today's
atmosphere. Earth is
believed to have formed
about 5 billion years ago. In
the first 500 million years a
dense atmosphere
emerged from the vapor
and gases that were
expelled during degassing
of the planet's interior.
Phases of Origin of
Atmosphere:
1) The gases of early
atmosphere may have
consisted of hydrogen (H2),
water vapor, methane
(CH4) , and carbon oxides.
Prior to 3.5 billion years ago
the atmosphere probably
consisted of carbon dioxide
(CO2), carbon monoxide
(CO), water (H2O), nitrogen
(N2), and hydrogen.
2) The hydrosphere was
formed 4 billion years ago
from the condensation of
water vapor, resulting in
oceans of water in which
sedimentation occurred.
3) The most important
feature of the ancient
environment was the
absence of free oxygen.
4) One billion years ago,
early aquatic organisms
called blue-green algae
began using energy from
the Sun to split molecules
of H2O and CO2 and
recombine them into
organic compounds and
molecular oxygen (O2).
Some of the
photosynthetically created
oxygen combined with
organic carbon to recreate
CO2 molecules. As oxygen
in the atmosphere
increased, CO2 decreased.
5) ) High in the
atmosphere, some oxygen
(O2) molecules absorbed
energy from the Sun's
ultraviolet (UV) rays and
opening to form single
oxygen atoms.
6) These atoms
combining with remaining
oxygen (O2) to form ozone
(O3) molecules, which are
very effective at absorbing
UV rays. The thin layer of
ozone that surrounds Earth
acts as a shield, protecting
the planet from irradiation
by UV light.
7) The presence of
ozone enabled organisms
(600 million years ago) to
develop and live on the
land.
Composition of
Atmosphere:
Basically, the atmosphere is
composed of three major
constituents, namely
v Gases,
v Water vapor, and
v Aerosols
Gases:
Air is mainly composed
of nitrogen, oxygen, and
argon, which together
constitute the major gases
of the atmosphere.
Water Vapor
Water vapor, though
considered in the category
of atmospheric gases,
needs separate
consideration because it is
very important constituent
of the atmosphere and is
responsible for different
types of condensation and
precipitation.
In fact, water vapor is a
gaseous form of water.
More than 90 percent of
the total atmospheric vapor
is found up to the height of
5 km.
Aerosols
1) Suspended particulate
matter (SPM) in the
atmosphere including solid
particles of varying sizes
and liquid droplets are
collectively called aerosols.
2) SPM includes dust
particles from volcanic
eruptions, exposed soil
cover, desert, rocks etc.;
salts particles from seas
and oceans; organic matter
( bacteria, seeds, spores,
pollen etc.); smoke and
soot.
(Figure and table from
Lutgens and Tarbuck,
The Atmosphere, 8th
edition
Structure of
Atmosphere:
The earth’s atmosphere
consists of a few zones or
layers like spherical shells.
The layered structure of
atmosphere has been
classified on two major
considerations. These are-
A) Thermal Characteristics
B) Chemical Composition
Thermal Characteristics
On the basis of the
characteristics of
temperature and air
pressure the layering
system of the atmosphere
has been classified
differently by scientists.
Generally, the atmosphere
is supposed to have been
formed of four vertical
layers. These are-
1) Troposphere
2) Stratosphere
3) Mesosphere
4) Thermosphere
Troposphere
The bottom layer,
where temperature
decreases with altitude,
is known as the
troposphere (from the
Greek for "turning
layer").
The troposphere is
approximately 12
kilometers thick, but
there are slight
variations. If the
temperature increases
with increasing altitude
in the troposphere,
then a temperature
inversion exists.
All the weather that we
are primarily interested
in, occurs in the
troposphere. The top
of the troposphere is
marked by the
tropopause.
Stratosphere
Above the tropopause
lies the stratosphere. It
gets it's name from the
Greek meaning
"stratified layer."
The layer is stratified
with the denser, cooler
air below the warmer,
lighter air. This leads to
an increase in
temperature with
height.
Since the stratosphere
isn't turbulent this is
where most planes like
to fly. The temperature
increases with height
until it reaches about
10°C at an altitude of 48
km.
The primary reason
that there is a
temperature increase
with altitude is that
most of the ozone is
contained in the
stratosphere.
Ultraviolet light
interacting with the
ozone causes the
temperature increase.
The boundary between
the stratosphere and
the next layer is called
the stratopause.
Mesosphere:
Above the stratopause,
the temperature again
decreases with
altitude. This layer is
called the mesosphere,
or "middle layer.“
The temperature
drops to ~-90°C near
the top of the
mesosphere where the
mesopause is located.
Thermosphere:
Ø Above the
mesopause is the
thermosphere, or
"warm layer.“
In the thermosphere
the temperature does
increase with height (to
>1000°C), but as we
have already seen, the
number of molecules
present are so few that
even thought they are
very energetic, they
have such a low
density, that
temperature as we call
it means very little.
Ø Above the
thermosphere lies the
exosphere ("outer
layer"). The boundary
between the two is
very diffuse.
Ø Molecules in the
exosphere have
enough kinetic energy
to escape the earth's
gravity and thus fly off
into space. This is
where helium
"disappears.“
Ø The outer part of the
mesosphere and the
thermosphere are
sometimes called the
ionosphere since
most of the molecules
and atoms are ionized
by the ultraviolet light
and other high energy
particles at this height.
The ionosphere is what
radio signals bounce
off.
Thermal Characteristics of
atmosphere:
Ø Originally, scientists
thought that
temperature decreased
continuously with
increasing height until
reaching absolute zero
(-273.16°C).
Ø This decrease of
temperature with
increasing altitude is
known as the
environmental lapse
rate and is
approximately
6.5°C/1000 m
(3.5°F/1000').
Ø In the figure below,
the environmental
lapse rate can be seen
graphically as the
decrease in
temperature with
increasing height.
(Figure 1-20, page 21 in
Lutgens and Tarbuck's
The Atmosphere, 2001)
Observed lapse rate and
the tropopause
Chemical Composition:
1) Homosphere
Main constituent gases are
N2 and O2.
2) Heterosphere
Extends: Above 90km
to 1000km
Molecular N2 layer
Ø Atomic O2 layer
Ø Atomic H2 layer