Thursday, 29 June 2017: 10:45 AM
Salon G-I (Marriott Portland Downtown Waterfront)
Sudden Stratospheric Warming (SSW) events influence the Arctic Oscillation and mid-latitude extreme weather. Observations show SSW events to be correlated with certain phases of Madden Julian Oscillation (MJO), but the teleconnection mechanism, its planetary wave propagation path and the teleconnection time scale are still not well understood. We study the Arctic stratosphere response to MJO forcing using two models. First, a comprehensive General circulation model (the Whole Atmosphere Circulation Model, WACCM) with standard and enhanced convection entrainment rate leading to stronger MJO. Second, an idealized dry dynamical core with and without idealized MJO-like forcing. We show that the frequency of SSW events increases significantly, and that the averaged polar cap temperature therefore increases significantly in response to stronger MJO forcing. Consistent with previous studies, we find that heat transport by stationary waves is a major contributor to the SSW response. We also find that MJO-forced transient waves propagate at about 70 mb toward the Arctic, and then travel toward the upper stratosphere, then leading to the stationary wave response. The cleaner results possible with the idealized model allow us to identify that the propagation time is of the order of 40-60 days, significantly longer than implied by previous studies. The horizontal propagation path is influenced by zonal jet exit regions, again in agreement with previous studies of remote tropospheric effects of MJO-forced planetary waves. Given that MJO is predicted to be stronger in global warming scenario, these results suggest that SSW events may become more frequent in a future warm climate, possibly with all the implications this has on tropospheric high latitude weather.
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