[A-AS06] Stratosphere-troposphere Processes And their Role in Climate

[AAS06-15] Detection of a climatological short break in the polar night jet in early winter and its relation to cooling over Siberia

★Invited Papers

*Yuta Ando^1,2, Koji Yamazaki³, Yoshihiro Tachibana², Masayo Ogi³, Jinro Ukita¹ (1.Faculty of Science, Niigata University, 2.Weather and Climate Dynamics Division, Mie Univesity, 3.Hokkaido University)

Keywords:Stratosphere, Rossby wave, Land-sea thermal contrast

The polar night jet (PNJ) is a strong stratospheric westerly circumpolar wind at around 65N in winter, and the strength of the climatological PNJ is widely recognized to increase from October through late December. Remarkably, the climatological PNJ temporarily stops increasing during late November. We examined this “short break” in terms of the atmospheric dynamical balance and the climatological seasonal march. We found that it results from an increase in the upward propagation of climatological planetary waves from the troposphere to the stratosphere in late November, which coincides with a maximum of the climatological Eliassen–Palm (EP) flux convergence in the lower stratosphere. The upward propagation of planetary waves at 100 hPa, which is strongest over Siberia, is related to the climatological strengthening of the tropospheric trough over Siberia. We suggest that longitudinally asymmetric forcing by land–sea heating contrasts caused by their different heat capacities can account for the strengthening of the trough.

The part of this presentation was published as the article, Ando et al. (2018).



Ando, Y., K. Yamazaki, Y. Tachibana, M. Ogi, and J. Ukita, 2018: Detection of a climatological short break in the polar night jet in early winter and its relation to cooling over Siberia. Atmospheric Chemistry and Physics, 18, 12639-12661, doi:10.5194/acp-18-12639-2018.