A new phase of land-atmosphere interactions in the East Asian jet variability during summer

The East Asian Jet (EAJ), a key upper-level westerly wind that controls monsoon circulation and precipitation patterns within the East Asian Summer Monsoon (EASM) system, has undergone multiple regime shifts since the mid-20th century. While transitions in the late-1970s and mid-1990s are well documented, a more recent shift in the early 2000s remains less well characterized. Here we identify a regime shift of the EAJ occurring in 2002/2003 through striking changes, manifested by an abrupt intensification in both the mean state and interannual variance of the jet. This shift coincides with significant surface warming over southern China and widespread drying across East Asia. Our analysis identifies two key features characterizing this transition: strengthening of the Tibetan Plateau High and emergence of enhanced soil moisture-temperature coupling variability over Inner East Asia. After 2003, coupling strength exhibits significant correlation with surface energy partitioning and lower-tropospheric thermal structure. This coupling variability is closely linked to jet fluctuations, indicating that enhanced jet variability is strongly mediated by land-atmosphere coupling processes. In addition, the intensified Tibetan Plateau High additionally contributes to jet intensification through modifications in upper-tropospheric circulation patterns. These results highlight the critical role of land-atmosphere interactions in EAJ variability and provide insights into potential linkages between drought conditions under global warming and monsoon circulation changes mediated through upper-level atmospheric flow.