Talk:Neutral density

Untitled 2017 topic

Hi all, Thanks for this page. I was asking myself a question about the sentence :"A neutral density surface is the surface along which a given water mass will move, remaining neutrally buoyant": let s say that two fluid particles with different salinity (S) temperature (θ) and pressure (p) :(θ1,S1,p1) and (θ2,S2,p2) (i.e. theta1≠theta2, S1≠S2 and p1≠p2) belong to the same neutral surface. Then according to this definition we must have: ρ(θ1,S1,p2)=ρ(θ2,S2,p2) AND ρ(θ1,S1,p1)=ρ(θ2,S2,p1) which means that (θ2,S2) belongs to the curve (in (θ,S) space) ρ(θ,S,p1)=ρ(θ1,S1,p1) but also that (θ1,S1) belongs to ρ(θ,S,p2)=ρ(θ2,S2,p2). This is possible only if θ1=θ2 and S1=S2 (or if p1=p2) which would mean that a neutral density surface is also a surface of both constant θ and S (or of constant pressure). Am I wrong somewhere or should this sentence be corrected ? Therm ocean (talk) 17:40, 13 February 2017 (UTC)

The discussion of a fluid parcel moving and remaining neutrally buoyant is only meant to refer to infinitesimal motions, which defines the neutral tangent plane. I've now clarified this on the page. The finite amplitude version, in your example and notation, is ρ(θ1,S1,(p1+p2)/2)=ρ(θ2,S2,(p1+p2)/2). GeoffStanley (talk) 18:28, 1 July 2019 (UTC)

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