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Modelling the Quasi‐Equilibrium Dynamics of the Atmosphere
Author(s) -
Cullen M. J. P.,
Norbury J.,
Purser R. J.,
Shutts G. J.
Publication year - 1987
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49711347704
Subject(s) - geostrophic wind , hydrostatic equilibrium , mesoscale meteorology , classification of discontinuities , diabatic , potential vorticity , geology , frontogenesis , drag , adiabatic process , physics , meteorology , mechanics , vorticity , vortex , mathematics , mathematical analysis , quantum mechanics , thermodynamics
The prime need in forecasting atmospheric motions is to predict the synoptic pattern accurately, and to fill in as much mesoscale detail on it as possible. the problem is difficult because the atmospheric fields contain almost discontinuous structures such as fronts and inversions, and the large‐scale flow may separate around mountains. This paper demonstrates that such phenomena may be described as quasi‐equilibrium structures where the fluid remains close to a minimum energy state. This minimum is shown to correspond to geostrophic and hydrostatic balance, and the implied quasi‐equilibrium evolution to correspond to the Lagrangian form of the geostrophic momentum equations. Examples of flows that can be treated include boundary layers separating at surface fronts and mountain blocking with associated drag. By including diabatic effects, the inland penetration of sea breezes can also be studied. the quasi‐equilibrium idea can be applied globally, but describes only a limited subset of tropical motions. Primitive equation models attempt to produce these structures by relying on explicit geostrophic adjustment. This paper presents evidence that this is not always adequate, especially when the structures contain discontinuities. Implicit algorithms are described which may be more effective.