Atmospheric Structure
The atmosphere
? The atmosphere is a thin blanket of gas that
envelops the earth.
? The gases that make up the atmosphere are
held close to the earth by the pull of gravity.
? With increasing distance from the earth’s
surface,the temperature,density,and
composition of the atmosphere gradually
change
? On the basis of air temperature,the
atmosphere can be divided vertically into four
major layers.
Atmospheric structure
Troposphere
? The troposphere is the layer from the earth’s surface to
the tropopause,which is at 10-15 km altitude depending
on latitude and time of year,(Mt,Everest 8.85km)
? As altitude increases,air temperature decreases at a
rate of about 3.5o per 1000 ft,The tropopause has a
temperature of about –57oC.
? The lower part of the troposphere interacts directly with
the surface of the earth–this part of the troposphere is
generally called air.
? The atmosphere in this layer is heated from below by
convection and radiation from the earth’s surface.
? Most of our weather occurs in the troposphere,
Stratosphere
? The stratosphere is the layer above the
troposphere and extends to about 50km.
? The temperature rises with increasing altitude,
reaching a maximum of about –1oC at the
stratopause.
? The ozone layer is in the stratosphere,Ozone
absorbs UV,causing the rising temperature with
altitude in this layer.
? The temperature structure keeps the air calm in
this layer,(That’s why jet aircraft fly in the lower
stratosphere!)
Mesosphere
? The mesosphere extends from the top of
stratopause to ~80 km.
? In the mesosphere,the temperature
decreases with altitude.
Thermosphere
? The layer of air above mesosphere is called
thermosphere.
? In the thermosphere,temperature rises with
altitude,caused by absorption of UV solar
radiation by N2 and O2.
The lower atmosphere
? The troposphere and the stratosphere
together are called the lower atmosphere.
? The lower atmosphere account for 99.9% of
total atmospheric mass
? The lower atmosphere is the domain of main
interest from an environmental perspective.
– Ozone depletion (stratosphere)
– Air pollution (troposphere)
Ionosphere
? Ionosphere is a region where ions and
electrons are most abundant,
? This region is located at altitude above 60km,
therefore lie within the mesosphere and
above.
Ionosphere
Ionosphere acts as
a conducting layer
in the upper
atmosphere that
would allow a
transmitted
electromagnetic
signal to be
reflected back
toward the Earth,
Ionosphere,Northern light (1)
Ionosphere,Northern light (2)
? Energetic events on the Sun can turn the solar
wind into an intense solar "gale” which injects
large numbers of energetic particles in the
Earth's magnetosphere.
Ionosphere,Northern light (3)
? The charged particles travel along the field
lines with so much energy that they
penetrate the ionosphere,where they hit gas
atoms and molecules,
? These collisions give off energy that we see
as colored light.
atmospheric pressure
The atmospheric pressure is the weight
exerted by the overhead atmosphere on a
unit area of surface
A B
h
vacuum
Mercury barometer
ghP HgA ??
Mass of the atmosphere
Ps,the global mean pressure at the surface,
Ps=9.84x104Pa.
R=6400 km,the earth radius
g=9.8m2/s,acceleration of gravity
g
PRm s
a
24 ?
?
Results,ma = 5.2x1018kg
24 R
gm
P as
?
?
Pressure profile
0
10
20
30
40
50
60
70
80
0, 0 1 0, 1 1 10 100 1000
P r e s s u r e,h P a
A
l
t
i
t
u
d
e
(
k
m
)
Barometric law
Where Ma,the molecular weight of air
g,acceleration of gravity
R,gas constant
T,temperature
z,altitude
)e x p ()0()( zRT gMPzP a??
What fraction of total atmospheric mass is
in the troposphere?
The troposphere contains all of the
atmospheric mass except for the fraction
P(tropopause)/P(surface) that lie above the
tropopause.
)(
)(1
s u r f a c eP
tr o p o p a u s ePF
tr o p ??
P(tropopause) = 100 hPa
P(surface)=1000hPa
Result,Ftrop =0.90
Units for pressure
? International System of Units,Pascal (N/m2)
? Hectopascal (hPa)
? mm Hg or Torr
? Millibar (mbar)
? psi (lb/in2)
1 atm = 1.01325 x 105 Pascal (Pa) = 1.01325 x 103hPa
1 atm = 760 mmHg = 760 Torr
1 atm = 1013.25 mbar
1 atm = 14,7 psi
The atmosphere
? The atmosphere is a thin blanket of gas that
envelops the earth.
? The gases that make up the atmosphere are
held close to the earth by the pull of gravity.
? With increasing distance from the earth’s
surface,the temperature,density,and
composition of the atmosphere gradually
change
? On the basis of air temperature,the
atmosphere can be divided vertically into four
major layers.
Atmospheric structure
Troposphere
? The troposphere is the layer from the earth’s surface to
the tropopause,which is at 10-15 km altitude depending
on latitude and time of year,(Mt,Everest 8.85km)
? As altitude increases,air temperature decreases at a
rate of about 3.5o per 1000 ft,The tropopause has a
temperature of about –57oC.
? The lower part of the troposphere interacts directly with
the surface of the earth–this part of the troposphere is
generally called air.
? The atmosphere in this layer is heated from below by
convection and radiation from the earth’s surface.
? Most of our weather occurs in the troposphere,
Stratosphere
? The stratosphere is the layer above the
troposphere and extends to about 50km.
? The temperature rises with increasing altitude,
reaching a maximum of about –1oC at the
stratopause.
? The ozone layer is in the stratosphere,Ozone
absorbs UV,causing the rising temperature with
altitude in this layer.
? The temperature structure keeps the air calm in
this layer,(That’s why jet aircraft fly in the lower
stratosphere!)
Mesosphere
? The mesosphere extends from the top of
stratopause to ~80 km.
? In the mesosphere,the temperature
decreases with altitude.
Thermosphere
? The layer of air above mesosphere is called
thermosphere.
? In the thermosphere,temperature rises with
altitude,caused by absorption of UV solar
radiation by N2 and O2.
The lower atmosphere
? The troposphere and the stratosphere
together are called the lower atmosphere.
? The lower atmosphere account for 99.9% of
total atmospheric mass
? The lower atmosphere is the domain of main
interest from an environmental perspective.
– Ozone depletion (stratosphere)
– Air pollution (troposphere)
Ionosphere
? Ionosphere is a region where ions and
electrons are most abundant,
? This region is located at altitude above 60km,
therefore lie within the mesosphere and
above.
Ionosphere
Ionosphere acts as
a conducting layer
in the upper
atmosphere that
would allow a
transmitted
electromagnetic
signal to be
reflected back
toward the Earth,
Ionosphere,Northern light (1)
Ionosphere,Northern light (2)
? Energetic events on the Sun can turn the solar
wind into an intense solar "gale” which injects
large numbers of energetic particles in the
Earth's magnetosphere.
Ionosphere,Northern light (3)
? The charged particles travel along the field
lines with so much energy that they
penetrate the ionosphere,where they hit gas
atoms and molecules,
? These collisions give off energy that we see
as colored light.
atmospheric pressure
The atmospheric pressure is the weight
exerted by the overhead atmosphere on a
unit area of surface
A B
h
vacuum
Mercury barometer
ghP HgA ??
Mass of the atmosphere
Ps,the global mean pressure at the surface,
Ps=9.84x104Pa.
R=6400 km,the earth radius
g=9.8m2/s,acceleration of gravity
g
PRm s
a
24 ?
?
Results,ma = 5.2x1018kg
24 R
gm
P as
?
?
Pressure profile
0
10
20
30
40
50
60
70
80
0, 0 1 0, 1 1 10 100 1000
P r e s s u r e,h P a
A
l
t
i
t
u
d
e
(
k
m
)
Barometric law
Where Ma,the molecular weight of air
g,acceleration of gravity
R,gas constant
T,temperature
z,altitude
)e x p ()0()( zRT gMPzP a??
What fraction of total atmospheric mass is
in the troposphere?
The troposphere contains all of the
atmospheric mass except for the fraction
P(tropopause)/P(surface) that lie above the
tropopause.
)(
)(1
s u r f a c eP
tr o p o p a u s ePF
tr o p ??
P(tropopause) = 100 hPa
P(surface)=1000hPa
Result,Ftrop =0.90
Units for pressure
? International System of Units,Pascal (N/m2)
? Hectopascal (hPa)
? mm Hg or Torr
? Millibar (mbar)
? psi (lb/in2)
1 atm = 1.01325 x 105 Pascal (Pa) = 1.01325 x 103hPa
1 atm = 760 mmHg = 760 Torr
1 atm = 1013.25 mbar
1 atm = 14,7 psi
