Dynamic Analysis of Two Canadian Warmings

Two Canadian Warmings (CWs) in December 1965 and November 1968 were chosen to investigate the circulation characteristics of CWs. Weak warming was observed at the middle and lower levels of the stratosphere in the two CW cases. Accompanying the weak warming, the westerly in the stratosphere changed to an easterly one, but lasted only a short while. The circulation anomaly in both CW cases was weaker compared to that in the stratospheric sudden warming (SSW). The “pre-conditioned” process that was observed in the SSW case was not observed in the two CW cases. As the main factor of the stratospheric disturbance, the upward planetary wave was enhanced prior to and after day 0 of the two CW cases, unlike in the SSW case. Arctic Oscillation (AO) evolution was employed to show the downward stratospheric vortex circulation anomaly. Although the two CWs caused an AO anomaly in the high stratosphere, the AO anomaly barely reached the lower troposphere.