Abstract. The East Asian winter monsoon (EAWM) is greatly influenced by many factors
that can be classified as anthropogenic forcing and natural forcing. Here we
explore the contribution of anthropogenic influence to the change in the
EAWM over the past decades. Under all forcings observed during 1960–2013
(All-Hist run), the atmospheric general circulation model is able to
reproduce the climatology and variability of the EAWM-related surface air
temperature and 500 hPa geopotential height and shows a statistically
significant decreasing EAWM intensity with a trend coefficient of
∼-0.04 yr−1, which is close to the observed trend. By
contrast, the simulation, which is driven by the same forcing as the All-Hist
run but with the anthropogenic contribution to them removed, shows no
decreasing trend in the EAWM intensity. By comparing the simulations under
two different forcing scenarios, we further reveal that the responses of the
EAWM to the anthropogenic forcing include a rise of 0.6∘ in surface
air temperature over East Asia as well as weakening of the East Asian
trough, which may result from the poleward expansion and intensification of
the East Asian jet forced by the change in temperature gradient in the
troposphere. Additionally, compared with the simulation without
anthropogenic forcing, the frequency of strong (weak) EAWM occurrence is
reduced (increased) by 45 % (from 0 to 10/7). These results indicate that
the weakening of the EAWM during 1960–2013 may be mainly attributed to the
anthropogenic influence.
Reversal of monthly East Asian winter air temperature in 2020/21 and its predictability