Decadal variations of the East Asian winter monsoon in recent decades

Observational studies indicated that the East Asian winter monsoon (EAWM) showed significant decadal variations and experienced an interdecadal weakening in the mid-1980s. How did the EAWM evolve thereafter? In this study, we investigate the decadal variations of the EAWM in the past three decades using five reanalysis datasets and one observational dataset. In total, five members of EAWM system are examined. In the lower troposphere, the Siberian high intensity becomes stronger around 2005 in all five reanalysis datasets, whereas the Aleutian low strengthens in the mid-1990s and weakens in the mid-2000s. The two subsystems show opposing changes in the past two decades. In the middle troposphere, the intensity of the East Asian trough remains weakening in recent decades only with some short-time strengthening around the years of 1995 and 2010. In the upper troposphere, the EAWM index based on the meridional shear of the East Asian jet stream at the 300-hPa level shows a weak positive trend since the 1990s. It has decadal variations similar to those of the East Asian trough. In the context of these members' changes, the low-level northerly wind index exhibits two cycles since the year 1980. This index increases in the mid-1980s, then decreases since the mid-1990s, and finally increases in the mid-2000s. Further analysis on the East Asian surface air temperature also reflects similar decadal variations. In summary, unlike the interdecadal shift in the mid-1980s, the EAWM members (i.e., the Siberian high, the Aleutian low, the low-level northwesterly wind, the East Asian trough and the East Asian jet stream) do not show consistent decadal variations over the past 30 years. The low-level members show more significant changes.