A multi‐model analysis of the East Asian monsoon changes in the Medieval Climate Anomaly and Little Ice Age

Using nine climate model simulations from the Paleoclimate Modelling Intercomparison Project Phase 3, the changes in the East Asian summer and winter monsoon, together with their associated atmospheric circulations in the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA), were investigated in this study. The East Asian summer monsoon strengthened (weakened) as a consequence of the increased (decreased) land–sea thermal contrast between the East Asian continent and the adjacent western North Pacific and South China Sea in the MCA (LIA). The East Asian winter monsoon (EAWM) changes varied across models, and differences were shown between the low latitudes and mid‐to‐high latitudes of the EAWM region. In the northern area, the EAWM intensified slightly due to a reinforced Aleutian Low during the MCA and decreased slightly because of the suppression of the Siberian High and the weakening and northward shift of the Aleutian Low during the LIA. In contrast, there are large inconsistencies among models during both periods in the southern EAWM region. Our results imply that model improvement is needed to reproduce the complex interacting processes over the low latitudes of East Asia. Taylor diagrams (Taylor, 2001) displaying the normalized pattern statistics of climatological meridional wind (a) at 850 hPa within the region of 20°–40°N and 105°–120°E between the eight climate models and observations in summer and (b) at 10 m and (c) 925 hPa within the regions of 25°–40°N and 120°–140°E together with 10°–25°N and 110°–130°E between the six and eight climate models, respectively, and observations in winter for the reference period of 1979–2005. Each number represents a model ID (see Table 1), and the observation is considered the reference (REF). Standard deviation and centred root mean square difference are normalized by the REF standard deviation. The radial distance from the origin is the normalized standard deviation of a model; the correlation between a model and the REF is given by the azimuthal position of the model, with the oblique dotted line showing the 99% confidence level, and the normalized centred root mean square difference between a model and the REF is their distance apart. In brief, the nearer the distance between a number and REF, the better the performance of the corresponding model.