Relation between the physical processes and spectral nudging in simulating regional climate

Regional climate models (RCMs) are one-way nested limited-area models that are used to downscale low-resolution atmospheric information, usually reanalyses or data simulated by general circulation model. In reality, errorneous long waves, which deviate from the driving coarse large-scale field, develop within the regional domain primarily because of systematic error of the regional model. Such waves reflect and interfere with shorter waves, distorting the circulation on regional scale. In addition, the change in domain-averaged temperature and moisture also impact the physical processes through changes in moisture availability and static stability. One way to mitigate such errors is to force the large scales not only at the lateral boundaries but also within the domain.

The sensitivity of regional climate simulation to cumulus parameterization schemes is examined using the RSM with and without spectral nudging. Scale-selective bias correction (SSBC) scheme is similar in function to the spectral nudging technique, but this new scheme is applied to NCEP Regional Spectral Model (RSM) with further refinement and simplification. The RSM simulation is evaluated against NCEP/DOE reanalysis and CPC precipitation data. To investigate impacts of spectral nudging on regional climate separately at different spatial scales, an isotropic digital spatial filter method will be applied.