Sensitivity to large-scale environmental fields of the relaxed Arakawa-Schubert parameterization in the NASA GEOS-1 GCM
Yan Yang -- Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida
I. M. Navon -- Department of Mathematics and Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida
Ricardo Todling -- NASA/DAO/General Sciences Corporation, Greenbelt, MD 20771
Weiyu Yang -- Environmental Modeling Center, NCEP/UCAR, Camp Springs, MD 20746
An adjoint sensitivity analysis of the RAS scheme in NASA's GEOS-1 GCM with respect to perturbations in large-scale environmental fields was conducted. The response functions were defined as measures of the strength of convective cloud precipitation, the cloud-induced heating and drying (moistening) in both instantaneous and time-integrated sense. The roles of different variables in producing variations on the response functions were evaluated and the most sensitive vertical levels of the perturbations were identified with the gradient provided by the adjoint model.
It was found that the potential temperature perturbations had significant impact on all the response functionals analyzed, especially on the convective precipitation. The perturbations at subcloud layers and at mid-troposphere from 500 to 600 hPa were found to be the most influential. The impact from the moisture fields was most significant on cloud heating and drying effects and the strongest influence came from the subcloud layers. The moisture perturbations at mid-troposphere also significantly influenced the cloud drying (moistening) effect. On the other hand, the cloud-induced heating and drying at levels between 400 and 600 hPa felt the strongest impact from perturbations in large-scale fields. The influence of the perturbations in the wind field was weaker but still provided reasonable sensitivity patterns.
The sensitivity analysis results obtained indicated that accurate grid-scale vertical profile of temperature and moisture, especially at subcloud layers and mid-troposphere between 500 to 600 hPa were essential for the accurate evaluation of the cumulus cloud effects. The implications of the results of this work for variational data assimilation were also discussed.