Wrong automatic definition of the laplacian coefficient

Context

The viscosity and diffusivity coefficients that are produced are incorrect when you activate:

• ln_traldf_lap = .true. and use 31 for nn_aht_ijk_t
• ln_dynldf_lap = .true. and use 31 for nn_ahm_ijk_t

The coefficients should be true to what is written in the commentary, namely it should be ahm = 1/2 Uv*Lv instead of ahm = 1/12 Uv*Lv which is what is computed for momentum. Similarly, for tracers, aht should be 1/2 Ud*Ld instead of 1/12 Ud*Ld.

• Branches impacted: current release and main
• No reference configurations or test cases are currently impacted by this bug
• Dependencies: Independent

Analysis

The laplacian coefficient will be 6 times smaller than expected. This will result in excessive diffusion of tracers and/or momentum in your configuration.

Fix

Replace 1/12 by 1/2 for the case "31" in ldftra.F90 and ldfdyn.F90