1. 5/4/10MET 61 topic 04 1 MET 61 Topic 4 Climate & Climate Dynamics

2. 5/4/10MET 61 topic 04 2 Climate –A time average of weather –Typically over 30 years Climate Variability –Variations year-to-year –Decade-to-decade

3. 5/4/10MET 61 topic 04 3 Climate is complicated! We must study: –External factors (oceans, sun etc.) –How the atmosphere behaves… Day-to-day Month-to-month season-to-season Year-to-year Decade-to-decade –Need to fully understand this variability to best understand anthropogenic changes

4. 5/4/10MET 61 topic 04 4 Source of Climate Variability? External? –SSTs –Biosphere –Cryosphere –Solar variations (e.g., sunspots) –Volcanic activity –Anthropogenic activity

5. 5/4/10MET 61 topic 04 5 Source of Variability? Internal? –Internal to the basic dynamics of the earth- atmosphere system? With fixed forcing, we would still year year-to- year variability etc. –This is internal variability

6. 5/4/10MET 61 topic 04 6 Present climate Annual surface pressures

7. 5/4/10MET 61 topic 04 7 World climate map

8. 5/4/10MET 61 topic 04 8 Present climate –Read §10.1 –The result of net radiative forcing –Solar heating (positive) – infrared cooling (negative) –Recall Ex. 4.6 (p.119)

9. 5/4/10MET 61 topic 04 9 –Solar constant (So) is 1368 W m -2 –Intercepted by area  R e 2 –And assuming an albedo of A=0.3 –Incoming radiation = (1-A).So.(  R e 2 ) –Outgoing is emitted by the earth’s surface (area 4  R e 2 ) according to Stefan-Boltzman –Outgoing radiation = .T e 4.(4  R e 2 )

10. 5/4/10MET 61 topic 04 10 –Equate and solve for T e.... T e = 255 K –This is the radiative equilibrium temperature –The observed global mean temperature is 288 K … 33 K warmer –Difference is due to the greenhouse effect of the atmosphere with greenhouse gases –Above is modified by emissivity factors etc.

11. 5/4/10MET 61 topic 04 11 –Fig. 10.2 → annual average net radiative driving of the earth-atmosphere system –High latitudes: deficit –Low latitudes: surplus  Equator → pole transport(s) required –Baroclinic eddies in mid-latitudes –Hadley cells in tropical latitudes –Oceans

12. 5/4/10MET 61 topic 04 12 –Fig. 10.5 → annual variation of incident radiation @ top of atmosphere → winter-summer driving of climate –Fig. 10.6 → net radiation @ top of atmosphere