On the mechanism of blocking in a stratified fluid

Abstract

The steady, two-dimensional motion which can occur when a body moves horizontally at large Richardson number is examined. Theoretical evidence is presented for two propositions: (i) The nature of the motion depends on whether the vertical thickness of the body is large compared with an intrinsic length scale of the motion. (ii) If the body is sufficiently thick, then diffusion or heat conduction are important, even if the Schmidt or Prandtl number is large. The notion of ‘near-similar’ solutions (§4) is used to obtain a description of the motion past a thick body which is likely to approximate the real motion everywhere except fairly close to the body surface (§5). It predicts a very long wake, at the core of which is a blocking column, both fore and aft of the body (§5). The same prediction is implied for the two-dimensional Taylor column in a rotating system (§6).