The impact of an envelope orography on low-frequency variability and blocking in a low-resolution general circulation model

Sensitivity experiments with a perpetual January version of a low-resolution general circulation model (GCM) are conducted to investigate the influence of different, nonzero specifications of orography on low-frequency variability (LFV) and blocking in the Northern Hemisphere. The use of an envelope orography leads to significant changes in the distribution of the LFV (periods 10-90 days) over the Northern Hemisphere. The impact of envelope orography on blocking, as measured by an objective criterion, is then examined. The changes in blocking distribution over the North Atlantic make the model's climatology more consistent with observations. It is hypothesized that the changes in LFV and blocking over the North Atlantic are a response to differences in the orographic forcing downstream of the Rocky Mountains. -from Author