The Impact of an Envelope Orography on Low-Frequency Variability and Blocking in a Low-Resolution General Circulation Model

Abstract

Abstract Sensitivity experiments with a perpetual January version of a low-revolution 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. Two 1200-day integrations are compared to examine the impact of an enhanced “envelope” orography. An ensemble of eight independent 90-day realizations is extracted from each simulation. Distributions of ensemble-mean statistics for the two simulations are presented, along with estimates of the statistical significance of the differences. The use of an envelope orography leads to significant changes in the distribution of the LFV (periods 10–90 days) over the Northern Hemisphere. When the LFV is partitioned into contributions from intramonthly ( 10–30-day periods) and intermonthly (30–90-day periods) fluctuations, it is found that the envelope orography significantly alters the distributions of intramonthly scale variability...