Winter Season Stratospheric Circulation in the SAMIL/LASG General Circulation Model

In this paper, we examine the performance of the 26-level version of the SAMIL/LASG GCM (R42/L26) in simulating the seasonal cycle and perpetual winter mean stratospheric circulation as well as its variability by comparing them with the NCEP/NCAR reanalysis. The results show that the model is capable of reproducing many key features of the climatology and seasonal variation of the stratospheric circulation despite that the model's mean polar vortex is stronger and more zonally symmetric compared to the observation. Further diagnosis of the results from a perpetual-January-run of the SAMIL/LASG GCM indicates that the dominant winter-season oscillation mode in the model's stratosphere exhibits a similar inter-seasonal timescale with similar spatial patterns as those inferred from the NCEP/NCAR reanalysis. In particular, the simulated polar vortex oscillation mode exhibits a dominant inter-seasonal timescale of about 120 days, and is accompanied with the simultaneous poleward and downward propagation of temperature anomalies in the stratosphere and the equatorward propagation of temperature anomalies in the troposphere. More encouragingly, the 26-layer version of the SAMIL/LASG GCM is able to produce three strong Stratospheric Sudden Warming events during the 1825 days of perpetual-January integration, with the polar westerly jet completely reversed for a few weeks without imposing any prescribed anomalous forcing at the lower boundary.