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Baroclinic‐wave life cycles, climate simulations and cross‐isentrope mass flow in a hybird isentropic coordinate GCM
Author(s) -
Thuburn John
Publication year - 1993
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.49711951108
Subject(s) - baroclinity , diabatic , advection , potential vorticity , isentropic process , coordinate system , curvilinear coordinates , physics , vorticity , tropopause , mass flux , spherical coordinate system , jet (fluid) , parametrization (atmospheric modeling) , mechanics , potential temperature , flow (mathematics) , meteorology , troposphere , adiabatic process , mathematics , vortex , radiative transfer , geometry , thermodynamics , quantum mechanics
Results are presented from a number of simulations using a global circulation model to compare the use of a δ or hybrid δ‐ p vertical coordinate with a hybrid δ‐θ‐ p vertical coordinate. In idealized baroclinic instability experiments, without diabatic processes, δ coordinates and δ‐θ‐ p coordinates give very similar results, with some suggestion of slightly improved Lagrangian potential‐vorticity conservation in the δ‐θ‐ p coordinate case. In climate simulations it has been necessary to include extra vertical diffusion in the presence of noisy temperature profiles in order to achieve stable integrations using δ‐θ‐ p coordinates (though this may by unnecessary if improved schemes for vertical advection and radiation are used.) The extra diffusion leads to a noticeably less noisy temperature profile around the tropopause. Large differences between δ‐ p coordinate integrations and δ‐θ‐ p coordinate integrations appear in the moisture field because the diabatic terms and vertical‐advection terms are computed in a different order, though the net moisture budget is not affected. Other diagnostics show that the two types of vertical coordinate give very similar results. Some examples are presented of a novel diagnostic: the accumulated cross‐isentrope mass flow. Global tracer conservation may be poor when hybird isentropic coordinates are used, unless care is taken to put the horizontal scale‐selective dissipation into the form of a flux divergence.