Morrison C++ zero-initializes cumulus tendency arrays and does not overwrite from input tendencies

[asalmgren]

Location

• Source/Microphysics/Morrison/ERF_AdvanceMorrison.cpp:633-635
• Source/Microphysics/Morrison/ERF_AdvanceMorrison.cpp:1080-1082
• Fortran reference: Source/Microphysics/Morrison/ERF_module_mp_morr_two_moment.F90:818-820

Problem

The C++ path explicitly zeros the local cumulus tendency arrays:

qrcuten_arr(i,j,k) = 0;
qscuten_arr(i,j,k) = 0;
qicuten_arr(i,j,k) = 0;

and then uses those values to populate qrcu1d/qscu1d/qicu1d for microphysics.

Why this is a bug

This effectively forces cumulus detrainment tendencies to zero in the C++ pathway unless they are explicitly reloaded later (they are not in this path). The Fortran pathway copies the real input fields into qrcu1d/qscu1d/qicu1d, so the two implementations diverge whenever those tendencies are nonzero.

Suggested patch

Populate qrcu1d/qscu1d/qicu1d from the incoming tendency fields (qrcuten_arr/qscuten_arr/qicuten_arr inputs), not fr
om zeroed local placeholders.

--- a/Source/Microphysics/Morrison/ERF_AdvanceMorrison.cpp
+++ b/Source/Microphysics/Morrison/ERF_AdvanceMorrison.cpp
@@
-            morr_arr(i,j,k,MORRInd::qrcu1d) = morr_arr(i,j,k,MORRInd::qrcuten_arr);
-            morr_arr(i,j,k,MORRInd::qscu1d) = morr_arr(i,j,k,MORRInd::qscuten_arr);
-            morr_arr(i,j,k,MORRInd::qicu1d) = morr_arr(i,j,k,MORRInd::qicuten_arr);
+            morr_arr(i,j,k,MORRInd::qrcu1d) = qrcuten_arr(i,j,k);
+            morr_arr(i,j,k,MORRInd::qscu1d) = qscuten_arr(i,j,k);
+            morr_arr(i,j,k,MORRInd::qicu1d) = qicuten_arr(i,j,k);

[AMLattanzi]

The tendency arrays noted here are defined only for the FORTRAN pathway and are blocked by an IFDEF; see here. However, the MORRInd::qrcuten_arr component is never initialized in the C++ code, but that data is copied into the MORRInd::qrcu1d component (as noted in the issue). The alternative solution would be to explicitly 0 the MORRInd::qr/s/icu1d values at the noted line. We could also remove the MORRInd::qr/s/icuten_arr components and save memory.