Presentation Information
[ACG68-P09]Co-occurrence of two summertime waveguide teleconnections over Eurasia
*Saori Sakai1, Yu Kosaka1 (1. Research Center for Advanced Science and Technology, the University of Tokyo)
Keywords:
Rossby wave,teleconnection
Westerly jet works as a waveguide for Rossby waves. In summer, the polar front jet (PFJ) blows along the northern coast of Eurasia, leading to a waveguide teleconnection. This PFJ teleconnection links an anomalous climate over Europe, Siberia and East Asia. There is another waveguide teleconnection over Eurasia, called the Silk Road teleconnection, which forms along the subtropical Asian jet. The two teleconnections are not necessarily independent, with some years featuring co-development of the two teleconnections. We investigate what brings the concurrent development of the two teleconnections in interannual variability and its influence on regional climate.
We apply an EOF analysis to monthly meridional wind anomalies over the Asian jet and PFJ regions to extract the PFJ and Silk Road wavetrain patterns, respectively, from the ERA5 reanalysis dataset and the d4PDF large ensemble AGCM simulations. For each of the EOF analysis, EOF1 and EOF2 represent the zonally orthogonal wave phases, and we obtain the joint PC as a linear combination of PC1 and PC2 to represent arbitrary zonal phases for each of the teleconnections. The analysis is conducted separately for individual calendar months from June to August to examine seasonality.
The maximum correlation between the PFJ and Silk Road joint PCs, obtained by sweeping over the range of combination coefficients for the two joint PCs, is significant in all of the three calendar months. The co-occurrence accompanies anomalies in blocking frequency in eastern Europe and the Ural region, suggesting its role in triggering the two wavetrains. There is a seasonality in the correlation between the two teleconnections, which increases towards late summer in both ERA5 and d4PDF. The seasonality in the waveguide structure contributes to this. Specifically, the PFJ waveguidability weakens toward late summer, allowing for Rossby wave transits to the subtropical waveguide. Besides the two waveguides get closer in late summer due to the southward shift of the PFJ. Seasonality in blocking high frequency over Northern Eurasia may also play a role, whose climatology and interannual variability peak in mid-summer and extend southward toward late summer.
We apply an EOF analysis to monthly meridional wind anomalies over the Asian jet and PFJ regions to extract the PFJ and Silk Road wavetrain patterns, respectively, from the ERA5 reanalysis dataset and the d4PDF large ensemble AGCM simulations. For each of the EOF analysis, EOF1 and EOF2 represent the zonally orthogonal wave phases, and we obtain the joint PC as a linear combination of PC1 and PC2 to represent arbitrary zonal phases for each of the teleconnections. The analysis is conducted separately for individual calendar months from June to August to examine seasonality.
The maximum correlation between the PFJ and Silk Road joint PCs, obtained by sweeping over the range of combination coefficients for the two joint PCs, is significant in all of the three calendar months. The co-occurrence accompanies anomalies in blocking frequency in eastern Europe and the Ural region, suggesting its role in triggering the two wavetrains. There is a seasonality in the correlation between the two teleconnections, which increases towards late summer in both ERA5 and d4PDF. The seasonality in the waveguide structure contributes to this. Specifically, the PFJ waveguidability weakens toward late summer, allowing for Rossby wave transits to the subtropical waveguide. Besides the two waveguides get closer in late summer due to the southward shift of the PFJ. Seasonality in blocking high frequency over Northern Eurasia may also play a role, whose climatology and interannual variability peak in mid-summer and extend southward toward late summer.