第七届青年地学论坛

The East Asian summer monsoon and winter monsoon (EASM and EAWM) are two important components of the East Asian monsoon system. However, the relationship between the two components during the Holocene remains debated in the observation. Here we examine a transient simulation to investigate the EASM-EAWM relation at different timescales during the Holocene. It is shown that the intensities of EASM and EAWM are positively correlated at orbital timescale but negatively correlated at multidecadal to millennial timescales. In contrast the positive correlation at orbital time scales that is forced by the seasonal insolation forcing, the negative EASM-EAWM relation at millennial and shorter timescales is caused mainly by the internal variability of the Atlantic Meridional Overturning Circulation (AMOC) and the subsequent teleconnection to East Asia via land-sea thermal contrast.
It should be noted that the relationship between EASM and EAWM may also depend on the definitions of the indices, which themselves remain ambiguous. The relationship between the wind-based EASM and the temperature-based EAWM is similar to that between the wind-based EASM and wind-based EAWM. This might be due to the fact that the AMOC can influence temperature along with the wind field over Eurasia through the westerly jet and the associated circumglobal teleconnection; it also confirms that EAWM can be represented either by DJF mean low level meridional wind or by DJF mean surface temperature over the eastern China. The NC precipitation based-EASM is also significantly negatively correlated with the wind based-EAWM at centennial timescale. This is consistent with the previous works suggesting that the NC precipitation can represent the intensity of EASM, i.e. the weakened/strengthened monsoon circulation is followed by the reduced/increased precipitation in North China. The SC precipitation-based EASM is correlated with the wind based-EAWM positively at decadal to centennial timescales, but negatively at multi-centennial to millennial timescales, and then positively again at the orbital timescale. This suggests that SC summer precipitation is not a good representation of the EASM intensity, because SC precipitation in JJA is affected by not only the EASM circulation but also other factors such as tropical cyclone.
 

East Asian monsoon,multi-scale