Fix double diffusion density ratio (not critical, since double diffusion is not used by default )#943
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…f absolute T/S ddmix computed alphaDT and betaDS from single-level absolute tracer values, making Rrho a ratio of absolute T and S rather than of their vertical density gradients. This triggered salt-fingering and diffusive-convection mixing continuously across virtually the entire ocean whenever double_diffusion=.true., regardless of actual stratification stability. Replace with the gradient form (T(nz-1)-T(nz), S(nz-1)-S(nz)) so that the scheme activates only at interfaces where the destabilising gradient exceeds the stabilising one, as the physics requires. Note: double diffusion is off by default (double_diffusion=.false.), so this bug has no effect on standard production runs.
JanStreffing
approved these changes
Jun 25, 2026
suvarchal
approved these changes
Jun 25, 2026
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Fix double diffusion density ratio using vertical gradients instead of absolute T/S
ddmix computed alphaDT and betaDS from single-level absolute tracer values, making Rrho a ratio of absolute T and S rather than of their vertical density gradients. This triggered salt-fingering and diffusive-convection mixing continuously across virtually the entire ocean whenever double_diffusion=.true., regardless of actual stratification stability.
Replace with the gradient form (T(nz-1)-T(nz), S(nz-1)-S(nz)) so that the scheme activates only at interfaces where the destabilising gradient exceeds the stabilising one, as the physics requires.
Note: double diffusion is off by default (double_diffusion=.false.), so this bug has no effect on standard production runs.