4 Central ideaConstraint 1: Ocean & Atmosphere are rapidly rotating fluids: geostrophy is the leading order dynamics.Constraint 2: The two fluids must transport energy poleward (cold parcels move equatorward and warm parcels poleward)
5 Central ideaThis brings a key distinction between basins (~ocean) and channel (~atmosphere)’s geometry:Basins: walls provide dP/dx and a large scale (eddy free) geostrophic heat transport is possible.Channels: no zonally integrated dP/dx and the heat transport must involve eddies and / or ageostrophic effects (e.g., Hadley cell).
6 OutlineThe energy constraintBasin dynamicsChannel dynamics
11 The energy constraintPoleward motionin ocean & atmosphere
12 Basin: Northern Oceans, Atmosphere BackgroundGeostrophic mass transport calculationHeat transportComplications…
13 oxygen distribution at 2500m A classic:oxygen distribution at 2500m(from Wüst, 1935).
14 oxygen distribution at 2500m A classic:oxygen distribution at 2500m(from Wüst, 1935).-Spreading from highlatitude North Atlanticsource region-Large spatial scaleof `tongue’ consideringthe narrowness of oceancurrents
20 Broecker, 2005NB: 1 Amazon River ≈ 0.2 Million m3/s
21 Atlantic ocean’s meridional overturning streamfunction NB: From an OGCMconstrained by data(Wunsch, 2000)
22 Can we measure the ocean circulation in basins using the Geostrophic calculation? All you need is the thermal wind:Coriolis parameterEast-westdensity gradientNorth-South velocityGradient with height
23 Global “inverse” ocean circulatioin and heat transport Ganachaud and Wunsch, 2003