Background
The authors write that "the east Asian winter monsoon (EAWM) is an important system in the Northern Hemisphere during boreal winter" - citing Lau and Li (1984), Chang et al. (2006) and Huang et al. (2012) - which season, in their words, "is characterized by the cold Siberian high and the warm Aleutian low at the surface, the low-level northerlies or northeasterlies along the coast of East Asia in the lower troposphere, the East Asian trough in the mid-troposphere, and the East Asian jet stream in the upper troposphere," citing Chen et al. (2000), Jhun and Lee (2004), Kang et al. (2006) and Zeng et al. (2011).

What was done
In the words of Gong et al., "model outputs from the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) are used to examine the climatology and inter-annual variability of the East Asian winter monsoon (EAWM)."

What was learned
With respect to unresolved difficulties, the six Chinese scientists report that (1) "the simulated surface air temperature still suffers from a cold bias over East Asia," that (2,3) "the inter-model spread is large for the lower-tropospheric meridional wind and precipitation along the East Asian coast," that (4) "the simulated variability is slightly weaker than in the observations," that (5) "the northeasterly anomalies over East Asia cannot be captured to the south of 30°N," due to what they call inadequacies of (6) "the EAWM index" and (7) "the ability of models to capture the EAWM-related tropical-extratropical interactions," that (8) "the models cannot capture the Pacific Decadal Oscillation," and, in much broader terms, that (9) the "changing ENSO-EAWM relationship can hardly be reproduced in CMIP models."

What it means
As is being found to be the case by many other researchers involved in the testing of various state-of-the-art climate models, almost all of them have significant deficiencies that have yet to be fully rectified.

References
Chang, C.-P., Wang, Z. and Harry, H. 2006. The Asian winter monsoon. In Wang, B. (Ed.). The Asia Monsoon, Praxis, p. 89-127.

Chen, W., Graf, H.F. and Huang, R.H. 2000. The interannual variability of East Asian winter monsoon and its relation to the summer monsoon. Advances in Atmospheric Sciences 17: 48-60.

Huang, R.H., Chen, J.L., Wang, L. and Lin, Z.D. 2012. Characteristics, processes, and causes of the spatio-temporal variabilities of the East Asian monsoon system. Advances in Atmospheric Sciences 29: 910-942.

Jhun, J.-G. and Lee, E.J. 2004. A new East Asian winter monsoon index and associated characteristics of the winter monsoon. Journal of Climate 17: 711-726.

Kang, L.H., Chen, W. and Wei, K. 2006. The interdecadal variation of winter temperature in China and its relation to the anomalies in atmospheric general circulation. Climatic and Environmental Research 11: 330-339.

Lau, K.-M. and Li, M.-T. 1984. The monsoon of East Asia and its global associations - A survey. Bulletin of the American Meteorological Society 65: 114-125.

Zeng, G., Wang, W.C., Sun, Z.B. and Li, Z.X. 2011. Atmospheric circulation cells associated with anomalous East Asian winter monsoon. Advances in Atmospheric Sciences 28: 913-926.