Analysis Of East Asian Winter Monsoon On Multiple Time Scales

In this study, combining the monthly mean reanalysis data during 1948~2015 from NCEP/NCAR and the proxy results of East Asian winter monsoon(EAWM) covering the Holocene, 16 different definitions of EAWM indexes were compared and analyzed. We mainly focused on the analysis of correlations between the different EAWM indexes and air temperature, precipitation and wind in East Asia. In addition, the spatial distribution of the variability of EAWM intensity during Holocene were also compared and analyzed. The results show follow:(1) Comparison among the 16 EAWM indexes indicates that the changes of EAWM intensity reflected by these indexes have a good consistency, with 95% indexes at a 99% confident level. Meanwhile, there are individual differences among the different indexes, implying that the different EAWM indexes may reflect the integrity or different region of EAWM, and then resulting in diversity of the emphasis of the indexes.(2) The change of EAWM intensity is weakening since 1949. There is a turning point of EAWM at 1980 s. In nearly 66 years, there are obvious decadal variation characteristics of the EAWM change, including several obvious periods of strong and weak. The periods spanning 1950 s to mid-1960 s and the end of 1970 s to the mid-1980 s are stronger, and the end of 1960 s to mid-1970 s and the mid-1980 s to today are weaker.(3) The intensity of EAWM is negatively related to air temperature and positively related to precipitation in East Asia during winter. Important regional boundaries are closely related to the positive correlation between EAWM and precipitation, suggesting that the correlation is significantly positive in eastern East Asia and oceanic regions, and weak positive in inland of East Asia affected by complicated earth surface. There are obviously regional characteristics in the eastern of Tibetan plateau, with windward of Japan Sea and Sinkiang.(4) The spatial distribution of 16 EAWM indexes is different with the height increasing. The spatial distribution is generally bounded by 40 °N and 20 °N from north to south which is associated with the correlation of “negative-positive-negative”, and bounded by 100 °E and 130 ° E from west to east which is associated with the correlation of “negative-positive-negative”. The spring spatial distribution is similar but weaker, compared to the pre-winter spatial distribution.(5) The EAWM responses to the changes of atmospheric circulation system at low and high latitude, through the influence of the teleconnection of coupled atmosphere–ocean. EAWM is negatively related to the Arctic Oscillation(AO) at high latitude and positively related to El Ni?o at low latitude.(6) The EAWM during the Holocene had different spatial distribution of EAWM in different periods at millennial. The spatial distribution of EAWM in the early Holocene(10~5.5ka) showed the structure of “weaken-strengthen-weaken” from north to south, and “weaken-strengthen” from west to east, which is similar to the spatial distribution of EAWM indexes at interdecadal timescales. But spatial distribution of EAWM during the mid-late Holocene(4.5~2ka) showed a consistently enhanced trend.