Arctic polar vortex variability in the Canadian middle atmosphere model

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Abstract
Arctic polar vortex variability in the Canadian Middle Atmosphere Model (CMAM) is documented. Two integrations of the CMAM are compared to assess the effects of parametrized non‐orographic gravity waves on the frequency and timing of stratospheric sudden warmings (SSWs), as well as on the potential for polar stratospheric cloud (PSC) formation. The first integration does not include parametrized non‐orographic gravity waves while the second integration does. The first integration captures the basic features of the observed northern hemisphere (NH) winter circulation although the polar night jet (PNJ) is significantly too weak and poleward shifted. Together with the weaker than observed PNJ are SSWs that occur too often and too early, resulting in an unrealistically low early to mid‐winter potential for PSC formation. Whereas, by design, the inclusion of parametrized non‐orographic gravity waves in the second integration significantly improves the southern hemisphere (SH) circulation, the strength of the NH PNJ is further reduced relative to the first integration, and the SSW frequency and PSC formation potential further degraded. Finally, the synoptic evolution and wavebreaking signature of the simulated and observed SSW events are compared through the application of a composite high resolution contour advection algorithm.