Determination of the Pressure Along a Closed Hydrographic Section. Part I: The Ideal Case

Abstract

The pressure along a closed hydrographic section can be correctly calculated from density data, in the ideal case of perfectly steady, geostrophic, density-conserving flow; and from dense, error-free data, excluding certain degenerate cues. A corresponding practical method, aimed at an estimate of the pressure from real hydrographic data, has been designed. The calculation is made by a minimization of the volume enclosed by the surface B = F(ro,P) in the P-ro-B space, where ro is the density. P = froz the potential vorticity, and B = B* + p0 the Bernoulli function, split in a known baroclinic part B* and an unknown pressure p0, defined at a chosen depth z0. The minimization is made under free variation of p0(s), as a function of the tangential coordinate s, the minimum volume is zero under the ideal conditions. Practically, one minimizes a moment rather than the volume, with identical results in the ideal case. The minimization requires an identification of ?corresponding points? (endpoints of the same streamline) from the P-conservation; this may become impractical in the presence of strong noise. In such cases an alternative method based on an integral equation expressing the detailed flux balance of P and B is proposed.