1. Aspects of Atmosphere-Ocean Circulation Brian Hoskins Director, Grantham Institute for Climate Change, Imperial College London Professor of Meteorology, University of Reading

2. mass of10m of ocean = mass of atmosphere thermal inertia of 2.5 m of ocean = that of atmosphere Atmosphere: well mixed gases + water vapour +… Ocean: water + salts + ….. 0 < ρ A < 1.31020 < ρ O < 1040 Some Basic numbers

3. Evaporation-Precipitation & Salinity of Ocean E-P Salinity

4. α 30 times and γ 2.10 4 larger for atmosphere Salinity (S) variations (~ 33-36% o ) as important as T variations for ocean Water vapour (0-50g/kg) impact on ρ often ignored for atmosphere Radiative transfer atmosphere: ½ solar through to surface of the Earth long wave loss to space from mid-troposphere ocean: solar absorbed in top 10m or so (55% in top 1m) long wave loss from top few mm atmosphere ocean Density variations & radiative transfer

5. Ocean 5km surface Atmosphere surface 50km Vertical structure T θ

6. Energy = 0 except near the surface Atmosphere Ocean Poleward energy transport by Hadley Cell = M (c p ΔT + ΔΦ + L Δq) ~ ( -4.8 + 7.5 - 1.8) 10 15 W = 0.9 PW

7. Ocean confined in basins Δp =p E - p W ∫ρv g dx = Δp/f However Antarctic Circumpolar Current Topographic confinement

8. From “Diagnostics of the Global Atmospheric Circulation”, UGAMP technical report #7 Winds, Currents & Mass Transport v A ~ 10 ms -1 v O ~ 1 cm s -1 → ρ A v A ~ ρ O v O Westerly wind & an easterly current! Mass flux by jets/currents ~ ρ V H W e.g. Gulf Stream mass flux ~ 10 3. 1. 1.10 3. 1.10 5 ~ 100.10 9 kg s -1 ~ 100 Sv 1 Sv (= 10 6 m 3 s -1 ) = 1.10 9 kg s -1 Westerly Jet mass flux ~ 0.6. 20. 4.10 3. 2.10 6 ~ 96.10 9 kg s -1 ~ 100 Sv H W V

9. Atmosphere positive vorticity independent of y + + + small f large f - + Ocean Low pressure/free surface independent of y y large f - - - - + Westward relative movement of Rossby Waves: contrasting arguments

10. Quasi-geostrophic potential vorticity: Ertel PV = ρ -1 ζ. grad θ Atmosphere ~ ρ(z) -1 (f+ξ) δθ/δz Ocean ~ ρ 0 -1 f/H = L R 2 /L 2 where L R = NH/f H N = 10 -2 s -1, f =10 -4 s -1 ; H = 10km, L R = 1000km;H = 100m, L R = 10km

11. PGFCF L L z Geostrophic motion in the atmosphere L Drag CF PGF Balance of forces with surface drag Frictional Stress at the atmosphere-ocean interface

12. = hAhA hOhO surface z τ

13. Wind-driven Ocean Circulation Sverdrup relation βv = f w z

14. Northward energy transport (Trenberth & Caron 2001) 4PW total A O NS Overturning circulations & northward energy transport Poleward energy transport = Mc p ΔT

15. Evaporation-Precipitation & Salinity of Ocean E-P Salinity

16. NH (DJF) Standard deviation of 2-6 day band pass filtered relative vorticity on 850 hPa. Hoskins and Hodges, 2002 Northern Hemisphere (Dec-Feb) time-mean Eady growth parameter in the lower troposphere. Shading indicates high values. Blacked areas are regions of high orography. Hoskins and Valdes, 1990 Storm-tracks

17. SOI: Tahiti – Darwin SLPNiňo3.4 SST El Niňo Southern Oscillation