Abstract
Significant water conservation errors were found in both the atmosphere-only and the coupled model simulations with the ne30L72 ACME v1.0_alpha7 model. Water conservation errors at different model resolutions (ne11L72, ne16L72, ne30L72, and ne120L72) are investigated. For the atmosphere component, we have identified several error sources, which include:
- large conservation error in the dynamical core that is related to the coupling between the tracer mass tendencies from model physics and the tracer transport scheme;
- error associated with inaccurate surface moisture flux used in CLUBB;
- error caused by the QFLX correction (in QNEG4), where QFLX is negative and the available surface moisture can not balance the downward flux;
- error due to clipping of negative tracers after each process (by QNEG3);
- internal conservation error in deep convection, CLUBB, and MG2 (including the internal clipping errors).
The error magnitude from individual sources changes with the model horizontal resolution. Solutions are found to eliminate the water conservation error from sources (1-4). By using an alternative physics-dynamics coupling method, the water conservation error in the ne30L72 atmosphere model decreases by ~50 times. The error can be further reduced by one order of magnitude if two new fixers for error sources (3-4) are used. Water conservation errors in recent (alpha 8+) AMIP and coupled simulations will also be discussed.