1. ATOC 4720 class29 1. How the energy balance is achieved in the earth-atmosphere system 2. The energy balance of the upper atmosphere 3. The energy balance of the troposphere

2. IR rad latent 21% 23% 7% sen

3. The mean planetary irradiance back into space • Assume the net energy flux through the earth’s surface is negligible, and energy stored in the atmosphere is not systematically changing, • Then at the top of the atmosphere, incoming energy should be balanced by outgoing energy:

4. S=1380W/m2 Incoming solar radiation Outgoing planetary radiation The earth’s radius A---planetary albedo

5. How the balance is achieved

6. The energy balance at the earth’s surface 23% 7% 21%

7. Balance at the top of the atmosphere 100 units incident: Out: 30% reflected 6% longwave radiation from earth 64% emission by atmosphere (38% by water and carbon dioxide molecules; 26% by clouds)

8. Balance in the atmosphere In: 19% absorbed solar radiation; 15% absorbed the earth’s IR radiation; 30% latent & sensible heat fluxes; Out: 64% IR emission (38% & 26% )

9. 2. The energy balance of the upper atmosphere Above the tropopause: absorption of solar radiation is important. Photoionization and photodissociation of various Gaseous constituents of the upper atmosphere by UV and X-ray.

10. Photoionization of the thermosphere (most above 90km, N2, O2, O gives rise to E- and F-layer): UV & X-ray . Due to this absorption, T in the thermosphere (Z>80km) increases with height to maintain thermal equilibrium; random molecular motion can conduct heat downward. (radiation is ineffective because of the thin air density). T is strongly influenced by solar activity. • Photodissociation of oxygen:

11. O--major consituent above 100km, although it is highly Reactive. [mean free path is long at high level] At lower levels: (20-60km, say), although O is trace constituent, it is important in forming ozone layer. [Mean Free path is lower at lower level] M: 3rd molecule to carry excess energy away from the reaction (3 body collision).

12. The Ozone layer UV: Not much absorbed by photodissociation, so O Quickly recombines with O2, maintaining ozone layer.

13. 3. The energy balance of the troposphere Troposphere: structure and dynamics are profoundly Influenced by the earth’s surface; Latent and sensible Heat fluxes account for 30% of the total 51% absorbed. Almost all solar radiation with Is absorbed above tropopause; Very little absorption in visible band (maximum solar Emission) Absorption of solar IR radiation mostly occurs in troposphere, Where water vapor is located.