Convective adjustment scheme in the generic PCM

IMPORTANT: This page concerns the convadj routine in the Generic physics package (by the way the latest version may be checked here on the trac: https://trac.lmd.jussieu.fr/Planeto/browser/trunk/LMDZ.GENERIC/libf/phystd/convadj.F

Overview of the convadj routine

The dry convective adjustment is simply a scheme which accounts for the fact that a thermally unstable profile will rapidly be mixed by unresolved (sub-grid-scale) vertical motion and brought back to being stable. This process will not only affect the temperature of the parcel but also tracers and winds (as the convective motion also transports momentum).

It can be turned on with the convadj=.True. keyword.

Description of assumptions and computations

• Estimation of whether a profile is thermally unstable is done by checking the sign of the vertical gradient of potential temperature $$\partial \theta / \partial z$$ (negative when unstable)
• Unstable regions are brought back to being adiabatic, i.e. such that : $$\partial \theta / \partial z = 0$$, while conserving the enthalpy of the column
• based on the "intensity" of the instability, estimated from the relative enthaply exchange necessary to restore the adiabaticity of the profile, related momentum mixing is evaluated and converted to tendencies on the horizontal winds of the air parcel. This momentum transfer evaluation is also used to estimate tracer transfer.

Mean molecular weight effect

If you have a condensing generic tracer and the virtual_theta_correction keyword is True, then the instability of the column is inferred from the gradient of the virtual potential temperature to account for the mean molecular weight effect.

References

See Hourdin et al. JAS 1993 https://doi.org/10.1175/1520-0469(1993)050%3C3625:MVATAS%3E2.0.CO;2