4:45 PM - 5:00 PM
[ACG36-18] Influence of the summertime waveguide teleconnection along the Eurasian polar-front jet on the East Asian climate through the Okhotsk High development
Keywords:Rossby wave, waveguide teleconnection
The polar-front jet (PFJ) over northern Eurasia in summer works as a waveguide for Rossby waves, leading to the summer waveguide teleconnection along the PFJ. This teleconnection can trigger an abnormal weather over Europe, Siberia and East Asia. A previous study finds that the PFJ teleconnection leads to development of the Okhotsk High especially in July. The Okhotsk High is a high-pressure system that forms over the Sea of Okhotsk in summer and one of the main factors that affect summertime climate in East Asia. In this study, we examine characteristics of this summertime PFJ teleconnection and its influence on regional climate through the development of the Okhotsk High, by analyzing the ERA5 reanalysis dataset.
We extract this teleconnection through an EOF analysis of interannual variability in summer 250 hPa meridional wind velocity over the PJF region (50ºN – 80ºN, 0º – 150ºE). EOF1 and EOF2 represent zonally extending wavetrain patterns with mutually orthogonal zonal phases. The difference of variance between EOF1 and EOF2 is small, suggesting that this teleconnection does not have a clear dominant zonal phase. This motivates us to examine arbitrary zonal phases of the teleconnection by linearly combining EOF1 and EOF2.
We examine the interannual correlation between the PFJ teleconnection and the Okhotsk High intensity. Despite that the PFJ is weaker in late summer than in early summer, there is significant correlation in certain zonal phases in each of June, July and August. The SLP anomaly regressed on the particular zonal phase of the PFJ teleconnection is positive over the Sea of the Okhotsk. However, the zonal phase with the highest correlation varies depending on the calendar month. In June and July, the positive SLP anomaly over the Sea of Okhotsk accompanies a deep high-pressure system tilting northward with the height. In August, by contrast, it shows a shallow high-pressure system. The common feature in each month is that the northeastly wind anomaly over the north-east sea of the mainland of Japan associated with the amplification of the Okhotsk High leads to the cool advection. Furthermore, especially in June, there is significant positive precipitation anomaly over the eastern Kanto and the eastern sea of the mainland of Japan, suggesting the relationship of Baiu.
We extract this teleconnection through an EOF analysis of interannual variability in summer 250 hPa meridional wind velocity over the PJF region (50ºN – 80ºN, 0º – 150ºE). EOF1 and EOF2 represent zonally extending wavetrain patterns with mutually orthogonal zonal phases. The difference of variance between EOF1 and EOF2 is small, suggesting that this teleconnection does not have a clear dominant zonal phase. This motivates us to examine arbitrary zonal phases of the teleconnection by linearly combining EOF1 and EOF2.
We examine the interannual correlation between the PFJ teleconnection and the Okhotsk High intensity. Despite that the PFJ is weaker in late summer than in early summer, there is significant correlation in certain zonal phases in each of June, July and August. The SLP anomaly regressed on the particular zonal phase of the PFJ teleconnection is positive over the Sea of the Okhotsk. However, the zonal phase with the highest correlation varies depending on the calendar month. In June and July, the positive SLP anomaly over the Sea of Okhotsk accompanies a deep high-pressure system tilting northward with the height. In August, by contrast, it shows a shallow high-pressure system. The common feature in each month is that the northeastly wind anomaly over the north-east sea of the mainland of Japan associated with the amplification of the Okhotsk High leads to the cool advection. Furthermore, especially in June, there is significant positive precipitation anomaly over the eastern Kanto and the eastern sea of the mainland of Japan, suggesting the relationship of Baiu.