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Aspects of Atmosphere-Ocean Circulation

This comprehensive overview of atmosphere-ocean circulation examines fundamental principles of mass distribution, thermal inertia, evaporation-precipitation balance, and energy transport. It highlights the critical role of salinity and temperature variations in the ocean, the importance of water vapor in the atmosphere, and the dynamics of atmospheric pressure systems. The influence of the Hadley Cell and oceanic currents, such as the Gulf Stream, is analyzed alongside the interactions between winds and ocean dynamics. Key methods and models to study these relationships are discussed, contributing to our understanding of climate and weather patterns.

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Aspects of Atmosphere-Ocean Circulation

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

  2. Some Basic numbers mass of10m of ocean = mass of atmosphere 0 < ρA < 1.3 1020 < ρO < 1040 thermal inertia of 2.5 m of ocean = that of atmosphere Atmosphere: well mixed gases + water vapour +… Ocean: water + salts + …..

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

  4. Density variations & radiative transfer atmosphere ocean α 30 times and γ 2.104 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

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

  6. Energy Atmosphere Ocean = 0 except near the surface Poleward energy transport by Hadley Cell = M (cpΔT + ΔΦ + L Δq) ~ ( -4.8 + 7.5 - 1.8) 1015 W = 0.9 PW

  7. Topographic confinement Δp =pE- pW Ocean confined in basins ∫ρvgdx = Δp/f However Antarctic Circumpolar Current

  8. Winds, Currents & Mass Transport Westerly wind & an easterly current! vA ~ 10 ms-1vO ~ 1 cm s-1 → ρAvA ~ ρOvO Mass flux by jets/currents ~ ρ V H W V H e.g. Gulf Stream mass flux ~ 103 . 1 . 1.103 . 1.105 ~ 100.109 kg s-1 ~ 100 Sv 1 Sv (= 106 m3 s-1 ) = 1.109 kg s-1 W Westerly Jet mass flux ~ 0.6 . 20 . 4.103 . 2.106 ~ 96.109 kg s-1 ~ 100 Sv From “Diagnostics of the Global Atmospheric Circulation”, UGAMP technical report #7

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

  10. Quasi-geostrophic potential vorticity: = LR2/L2 where LR = NH/f N = 10-2s-1, f =10-4s-1; H = 10km , LR = 1000km; H = 100m, LR = 10km Ertel PV = ρ-1ζ. grad θ Atmosphere ~ ρ(z)-1 (f+ξ) δθ/δz Ocean ~ ρ0-1 f/H H

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

  12. z hA surface τ hO =

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

  14. Overturning circulations & northward energy transport N S Poleward energy transport = McpΔT Northward energy transport (Trenberth & Caron 2001) total 4PW A O

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

  16. Storm-tracks 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 NH (DJF) Standard deviation of 2-6 day band pass filtered relative vorticity on 850 hPa. Hoskins and Hodges, 2002

  17. El Niňo Southern Oscillation SOI: Tahiti – Darwin SLP Niňo3.4 SST

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