第九届青年地学论坛

The intraseasonal oscillation of East Asian jet stream plays a crucial role in the formation and development of persistent climate anomalies over East Asia. This study examines the decadal changes in the intraseasonal variability (ISV) of the East Asian jet stream and investigates the possible reasons. It is found that the zonal winds over East Asia show notable ISV with a period of 10–25 days. The variance of intraseasonal East Asian zonal winds exhibits a significant decrease around 2000, mainly contributed by the weakened ISV of westerlies within the key region of East Asian polar front jet (EAPJ). The EAPJ experienced remarkable ISV changes in both intensity and location. The ISV of EAPJ intensity was weakened around 2000 due to decreased frequencies of both the extremely strong and weak cases, whereas the ISV of EAPJ location was enhanced with the southward shifts increased more than the northward ones. In the meantime, the dominant mode of EAPJ intraseasonal variation has changed from its intensity change to position shift since 2000. The decadal ISV changes and mode transition of EAPJ are closely associated with the modulation of lower-level circulation over Eurasia. The weakened ISV of meridional winds over Ural region after 2000 is favorable for an intraseasonal circulation pattern change from a continental-scale cyclonic anomalous pattern to a meridional dipole structure across the Eurasia, resulting in regime shifts of East Asian temperature and its meridional gradient through temperature advection. The intraseasonal temperature gradient patterns display ISV changes parallel to those of EAPJ around 2000, indicating that the thermal anomalies are effective in leading to corresponding EAPJ variations via thermal wind relationship. Furthermore, the circulation modulation is related to strengthened Arctic warming and weakened temperature variability over Barents sector, which may further be linked to sea ice reduction in the Barents Sea.

decadal change,intraseasonal variability,East Asian jet stream,polar-front jet