lizziel
commented
4 years ago This update will go into 12.7.0. The relevant files moved to the GEOS-Chem repository. See https://github.com/geoschem/geos-chem/commit/9516c8762ef075453ca8cc0ec533b36110e2cf40.
In GEOS-Chem Classic the species concentration is scaled by the ratio of current and previous delta dry pressures across the box each timestep to conserve mass. In GCHP the scaling is applied by the finite volume cube-sphere dynamical core (FV3) and therefore is not necessary. However, if advection is turned off, the scaling is required.
There used to be functionality that the scaling was applied if (1) not the first timestep and (2) advection was off. The first timestep was skipped because the previous delta dry air pressure (from the last timestep) was not available to use in the scaling. This worked fine for single runs but caused discrepancies between multiple consecutive runs versus a single long run over the same time period. For this reason we turned off the scaling temporarily.
A better solution is to turn on the scaling if (1) advection is off, it is the first timestep, and the previous dry air pressure is in the restart file, or (2) it is not the first timestep and advection is off. This solution requires saving out the delta dry air pressures to the restart file, done by adding it to the MAPL internal state.