09:30 〜 09:45
[ACG32-03] Dynamics of the summertime waveguide teleconnection along the Eurasian polar front jet and its change under global warming
キーワード：経年変動、ロスビー波の導波管
The polar front jet (PFJ) over the summertime northern Eurasian sector is associated with a large meridional gradient of temperature with the Arctic Ocean. It is one of the main pathways thorough which the teleconnections affect summer climate in East Asia, but understanding of how much influence this PFJ teleconnection has on the frequent heatwave occurrence and its modulations under global warming is limited. In this study, we investigate dynamics of this summertime PFJ teleconnection, its influence on climate, and its changes under global warming, by using a reanalysis dataset and a large ensemble AGCM simulation dataset which consists of historical and global warming simulations.
We extract this teleconnection through an EOF analysis for interannual variability of summer (from June to August) 250 hPa meridional wind anomalies over the PFJ region. Both the leading (EOF1) and second (EOF2) modes feature a zonal wave train pattern with a wavenumber of about 4 from the North Atlantic through Siberia to Far East and the North Pacific. Our analysis based on a reanalysis dataset and the large ensemble historical simulations suggests that EOF1 and EOF2 are not well separated, and the fraction of variance of EOF1 and EOF2 is close even if they are separated due to the large ensemble size in historical simulations. Moreover, the zonal phase of d4PDF each member EOF1 and EOF2 widely varies respectively. These results suggest that this teleconnection does not have an apparent dominant zonal phase, unlike the other teleconnection along the subtropical Asian jet. We also found that this monthly teleconnection affects the development of the surface Okhotsk high, which brings cool summer to northern Japan.
In the global warming simulations, we found that this teleconnection shifts poleward, corresponding to the poleward shift of the PFJ. In addition, the PFJ teleconnection becomes stronger in its downstream portion, which is likely related to its stronger influence on the Okhotsk High in late summer. Our evaluation of the PFJ teleconnection strength using the associated kinetic energy (KE) and available potential energy (APE) reveals that the circulation anomalies associated with the PFJ teleconnection weaken under global warming, especially in the troposphere.
We extract this teleconnection through an EOF analysis for interannual variability of summer (from June to August) 250 hPa meridional wind anomalies over the PFJ region. Both the leading (EOF1) and second (EOF2) modes feature a zonal wave train pattern with a wavenumber of about 4 from the North Atlantic through Siberia to Far East and the North Pacific. Our analysis based on a reanalysis dataset and the large ensemble historical simulations suggests that EOF1 and EOF2 are not well separated, and the fraction of variance of EOF1 and EOF2 is close even if they are separated due to the large ensemble size in historical simulations. Moreover, the zonal phase of d4PDF each member EOF1 and EOF2 widely varies respectively. These results suggest that this teleconnection does not have an apparent dominant zonal phase, unlike the other teleconnection along the subtropical Asian jet. We also found that this monthly teleconnection affects the development of the surface Okhotsk high, which brings cool summer to northern Japan.
In the global warming simulations, we found that this teleconnection shifts poleward, corresponding to the poleward shift of the PFJ. In addition, the PFJ teleconnection becomes stronger in its downstream portion, which is likely related to its stronger influence on the Okhotsk High in late summer. Our evaluation of the PFJ teleconnection strength using the associated kinetic energy (KE) and available potential energy (APE) reveals that the circulation anomalies associated with the PFJ teleconnection weaken under global warming, especially in the troposphere.