[A-CG30] Extratropical oceans and atmosphere

[ACG30-08] The Northern Annular Mode phase distorted by the Boundary Current Synchronization

*Tsubasa Kohyama¹, Yoko Yamagami², Shoichiro Kido², Fumiaki Ogawa³, Hiroaki Miura⁴, Hiroaki Tatebe² (1.Department of Information Sciences, Ochanomizu University, 2.Japan Agency for Marine-Earth Science and Technology, 3.Hokkaido University, 4.The University of Tokyo)

Keywords:Boundary Current Synchronization, Northern Annular Mode, Extreme weather, air-sea interaction

Synchronized variability between two Northern Hemispheric western boundary currents, the Boundary Current Synchronization (BCS), is associated well with meridional migrations of the atmospheric jet stream. Based on observational evidence, BCS exhibits covariability with the Northern Annular Mode (NAM), the most prominent internal mode of atmospheric variability that controls the latitudinal position of the jet stream in Northern Hemispheric winter. Therefore, in this study, we have performed a set of high-resolution pacemaker experiments where sea surface temperatures in the two boundary current regions are strongly relaxed to a preindustrial control run. These eddy-permitting pacemaker runs show that BCS actively supports the existence of extreme NAM events, which directly affects the abnormal weather events in winter. The extent to which boundary currents affect the NAM phase varies among different ensemble members, so the BCS influence on NAM is sensitive to stochasticity.