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.
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!)
atmospheric pressure
The atmospheric pressure is the weight exerted by the overhead atmosphere on a unit area of surface
vacuum
h A B
PA Hg gh
Mercury barometer
– 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.
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.
Ftrop P(tropopause ) 1 P( surface)
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)
Ionosphere: Northern light (3)
• The charged particles tines 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.
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
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.
Mass of the atmosphere
ma g Ps 4R 2
4R 2 Ps ma g
Ps: the global mean pressure at the surface, Ps=9.84x104Pa. R=6400 km, the earth radius g=9.8m2/s, acceleration of gravity Results: ma = 5.2x1018kg
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.
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.
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.
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.
Pressure profile
80 70 60
Altitude (km)
50 40 30 20 10 0 0.01
0.1
1
10
100
1000
Pressure, hPa
Barometric law
Mag P( z ) P(0) exp( z) RT
Where Ma: the molecular weight of air g: acceleration of gravity R: gas constant T: temperature z: altitude