Erroneous adjoint code in subroutine 'tra_ldf_iso_adj' of module 'traldf_iso_tam'

[sam]

As pointed out in ticket #1482, the test of the tangent-linear and adjoint subroutines of module 'traldf_iso_tam' fails after fixing the computation of the lateral diffusion coefficients or by selecting non-zero additional horizontal tracer diffusion.

Analysis of the relevant code revealed that the adjoint subroutine lacks the setting to zero of variables 'aditad' and 'adjtad' at the end of the loop over the tracer index, which would be required for it to correspond to its tangent-linear counterpart. At the end of the innermost body of the final nested loop structure (loop over the tracer index and the three spatial indices), both 'zditad(ij,jj,jk) and 'zditad(ij,jj,jk)' could be set to zero in order to make the loop correspond to the respective section of the tangent-linear counterpart of the subroutine. Further, at the end of the body of the outermost level of this loop (loop over the tracer index), the two lines 140 and 141 of the tangent-linear code should be mirrored in the adjoint code.