8: Infrared (Longwave) Radiation

Question 1

Energy Absorbed (formula)

Answer 1

Energy absorbed = Area x solar flux x (1 -albedo)

= (pi r2) x (Si) x (1 - alpha)

Question 2

Solar flux

1) Define
2) Denoted with
3) Measure with

Answer 2

1) Amount of radiation per unit area
2) Si
3) Pyranometer

Question 3

Energy Emitted (formula)

Answer 3

Energy emitted = Surface area x emissivity x constant x T^4
= 4 pi r2 x e x o x T^4
(where e = ~0.94 - land surface)
(4 pi r2 = energy emitted across the globe so total surface area
Stefan-Boltzmann equation with added e

Question 4

energy emitted = energy absorbed

equilibrium

Answer 4

energy emitted = energy absorbed
(4 pi r2)(e)(omega)(T^4) = (pi r2)(Si)(1-alpha)
T^4 = Si)(1-alpha)/ (4)(e)(omega)

Question 5

If earth’s temperature was solely a function of radiation absorbed & reflected at the surface,

1) What temperature would it be?
2) Where does the additional source of heat come from

Answer 5

1) 255 K (-18 *C)

2) Interactions of the outgoing infrared radiation with the atmosphere (GHGs)

Question 6

Infrared images on:

1) Cloud temperature
2) Land

Answer 6

1) Brighter the white, the cooler the cloud, the higher it is
2) Land is warmer so it is dark

Question 7

Measuring infrared radiation

1) shortwave
2) longwave

Answer 7

1) easy to measure as anything that is hot emits and wont be emitting infrared
2) much more difficult as everything (>0 K) emits infrared

Question 8

Shortwave radiation

1) Absorption
2) Emitted
3) Scattering
4) Reflection

Answer 8

1) Weak 
(except for UV)
2) Very little to none 
(due to air temperature)
3) By dust & aerosols
4) By clouds

Question 9

Longwave radiation

1) Absorption
2) Emitted
3) Reflection

Answer 9

1) Significant
(Due to GHGs)
2) Significant
(due to airs temperature)
3) Insignificant 
(longwave emitted from everything at a similar range)

Question 10

Radiation 
1) Formula
What denotes
2) T
3) r
4) a

Answer 10

1) T + r + a = 1
2) Transmissivity
3) Reflectivity (only shortwave radiaiton)
4) Absorptivity

Question 11

Radiation

Question 12

Greenhouse Effect (closed system)

Answer 12

No convection, advection or clouds
Water vapor trapped
Shortwave radiation penetrates through glass
Emitted longwave radiation is trapped

Question 13

Greenhouse Effect (Atmospheric)
1) Is there convection, advection or clouds?
2) Transmissivity 
(higher or lower for shortwave)
3) Absorptivity
(higher or lower for shortwave)

Answer 13

1) Convection, advection & clouds
2) Transmissivity of atmos to shortwave is much higher than longwave
3) Absorptivity of atmos to longwave is much higher than shortwave

Question 14

Greenhouse Effect

1) Where does it depend on
2) Which greenhouse gas/es has the longest window in which to absorb long wavelengths
3) Which greenhouse gas/es has the shortest window in which to absorb long wavelengths

Answer 14

1) Troposphere
2) H2O (Most important GHG)
3) CO2 & O3 (Ozone) but mainly in stratosphere, so insignificant