Interactions of Synoptic and Planetary Waves: Scale-Dependent Forcing of a GCM

Abstract

Abstract In order to better understand planetary wave–synoptic wave interactions in the atmosphere, and to develop a tool for further studies, the authors have applied a wavenumber-dependent external forcing to a general circulation model (GCM). The forcing constrains various length scales of the GCM to be close to those in the evolving analyses of the European Centre for Medium-Range Weather Forecasts and the National Centers for Environmental Prediction. The forcing acts either on the planetary waves (PW, defined as zonal wavenumbers 0–5), the synoptic waves (SW, defined as zonal wavenumbers 6–20), the synoptic waves plus the zonal mean (SW0), or the synoptic waves plus the zonal mean and wavenumber 1 (SW01). The form of the forcing is a linear relaxation to the (evolving) analyses with a time constant of 8 h. This forcing is applied only to the temperature and vorticity equations of the GCM, which has a spectral truncation of T42. Control integrations of length 30 days have been run starting on 15 Dece...