Response of the Northern Stratosphere to the Madden-Julian Oscillation During Boreal Winter

In this study, the effects of the Madden-Julian oscillation (MJO) on the northern stratosphere during boreal winter are investigated, especially in cases with the absence of a stratospheric sudden warming (SSW) event. During the wintertime, the polar cap temperature is expected to increase following MJO phase 2 (P2), P3, P4, and P7. However, the responses after P2 and P3 are much weaker if the dates from 50 days before to 50 days after the SSW central days are excluded from the composite. This result implies that the stratospheric polar warming following MJO P2 and P3 is sensitive to the occurrence of SSWs. After excluding the SSW events from the composite, the subsequent temperature anomalies strengthen and become more significant approximately 30 days after MJO P4 and 10 days after MJO P7. Planetary wave (PW) anomalies are enhanced in the midlatitudes of the upper troposphere, lagging MJO P4 by 15-25 days and lagging MJO P7 by 5-15 days. Thus, the upward propagation and dissipation of PWs in the stratosphere are significantly enhanced, further strengthening the Brewer-Dobson circulation in the Northern Hemisphere stratosphere. The WN1, which is induced by the MJO in the stratosphere, is the dominant component of PW perturbation. The enhanced PW dissipation in the high latitudes of the stratosphere is weaker in terms of lagging MJO P4, so the zonal wind and temperature anomalies after MJO P4 are less significant in the polar region, especially in the lower stratosphere.