Midterm Flashcards
Why doesn’t gravity collapse the atmosphere?
Pressure Gradient Force
How does PGF function?
Exerted upwards by atmosphere which balances gravity / air is directed from high pressure to low pressure
How are molecules attracted to Earth’s surface?
Gravitational Force
Force Equation
Mass x acceleration
What is pressure?
Force over a given area
How does the vertical profile of atmo behave?
Pressure decreases with altitude in the atmo.
What is hydrostatic balance?
The balance between the downward gravitational force and the upward PGF
Pressure equation
force/area
What does isothermal atmosphere assumption mean?
constant temperature of entire atmosphere
What is the solar luminosity value?
3.87 x 10^26
What is the solar constant?
1368
Solar luminosity definition
the total rate of energy released by the sun
How do we find solar constant?
using mean distance between Earth and the sun, we get a constant solar irradiance value
How do we use solar constant?
Represents the annual average solar irradiance value
How does Earth maintain a constant temperature?
Energy In = Energy out
If the energies do no equal what happens?
Earth’s temperature changes
What does disk Earth do?
receives solar radiation over the area of the disk
What does sphere Earth do?
Emits radiation over the surface area of a sphere
What is the emission temperature of Earth?
255K
How is most of radiation emitted?
Most are emitted to space via the atmosphere, not the surface (to maintain energy balance)
Zero dimensional energy balance model?
Transparent atmosphere, the surface temperature would equal the emission temperature
Single-layer atmosphere model
Assuming that the atmo is completely transparent to incoming radiation and completely opaque to outgoing radiation
What does the single-layer atmo model show?
The surface temp increases by a factor of 2 and 1/4 times the emission temperature.
What are “Atmospheric Windows”?
Places where energy passes through to space
What is Planck’s Law of blackbody emission?
Emission from a blackbody has a characteristic frequency distribution that depends on the object’s temperature.
What kind of wavelength does the Earth emit?
Longwave
What kind of wavelength does the Sun emit?
Shortwave, can pass through the atmosphere without being absorbed (scattered)
Why is a greenhouse gas a greenhouse gas?
Dipole molecular makeup
How are they able to absorb?
By rotating and vibrating
How do greenhouse gases interact with electromagnetic radiation?
molecular vibration and rotation
How does the molecule vibrate?
Dipole moment, causes it to vibrate and then absorb the radiation as kinetic energy
Why is is CO2 still able to be a greenhouse gas?
Even though it is not a dipole, the double polar bonds can cause it to become asymmetric and then vibrate.
Can CO2 absorb via rotation?
No, rotation does not induce a dipole moment
What does the blue jagged line on MODTRAN show?
The intensity of radiation at different wavelengths coming from the Earth/atmosphere that reaches the satellite
Why does the blue line not follow theoretical black body curve?
atmosphere emits energy at different frequencies, lower intensity because the atmosphere is colder
What are absorption bands?
when energy is remitted at a colder temperature (example CO2 window)
Why do gases absorb different wavelengths of infared energy?
Each gas molecule has different vibrational and rotational frequencies
What does a temperature profile tell us about IR radiation absoption?
radiation at wavelenghts is emitted to space from the top of the troposphere due to the cold temperatures
What is band saturation?
complete absoption of radiation at a specific wavelength band
When adding CO2, why does the window widen?
Broadening
Doppler broadening
Movement of molecules relative to photons allows a broader range of frequencies of radiation to interact with the molecule
Pressure broadening
Collisions between molecules transfer energy during radiative transitions, allowing photons with a broader range of frequencies to interact with the molecule
Where is pressure broadening most important?
Lower atmosphere
How does the greenhouse effect flow?
Logarithmically
Shortwave via clouds
Cloud impacts on incoming solar radiation
Longwave via clouds
Cloud impacts on outgoing longwave radiation
Which cloud warms the climate?
High clouds
Low Cloud emission temperature?
High
High cloud emission temperature?
low
Why does the low cloud have a high emission temperature?
it is closer to the surface, so the outgoing radiation from the surface versus the cloud will be similar
