Regime shift of Jet over East Asian summer Monsoon in the early 2000s: its detection and dynamical driver

The phase shift of climatic systems in decadal or interdecadal scale, also called as regime shift has occurred in East Asian Summer Monsoon (EASM) in the past. For example, the shifts of the late 1970s, mid 1990s, and early 2000s are the typical examples. Before and after these shifts, dominant teleconnection mode affecting the EASM had changed. On the other hand, the shift of early 2000s has not extensively investigated. Here, it is examined the characteristics of this particular shift in relation to variability of East Asian jet during summer. First, regime shifts earlier and in the early 2000s are detected based on the variance of summer East Asian jet. Second, the teleconnection pattern that influence summer East Asian jet was changed from the Atlantic-Eurasian (AEA) pattern to distinctly different zonal pattern around extratropical region of Eurasian. Finally, it was found that after this regime shift the land-atmosphere coupling induced by variability of soil moisture also strengthened. It is hypothesized that enhanced linkage between jet in the upper atmosphere and surface heat flux over Inner East Asia is a key mechanism of enhancing variability of the East Asian summer jet, i.e., the regime shift in 2000s. These results imply that over drier region, the regional climatic system might response more sensitively to regional-scale change on surface level than large-scale influence, such as wave-train.