During recent decades, the overall amount of Eurasian snow has decreased. This change is closely related to the amount of precipitation that falls over China. These observed features can be predicted by the US National Centers for Environmental Prediction Climate Forecast System, version 2 (CFSv2), several months in advance.

One of the most important advances in the study of Asian climate was the discovery of the strong link between the monsoon and the El Niño-Southern Oscillation (ENSO). In many cases, being able to predict Asian climate largely depends on the predictability of ENSO.

However, it has been found that the connection between Asian climate and ENSO has been weakening over recent decades. Scientists are now paying more attention to the effect of temperatures over Eurasia on the Asian climate; some studies have already reported that these are playing a more important role in Asian climate variations than ever before.

In winter, snow covers about 60% of the Eurasian continent and can influence its climate in several ways: by increasing the surface albedo; by increasing the amount of infrared heat lost from via high emissivity; and by serving as a thermal insulator thanks to its low thermal conductivity. Melting snow can also act as a sink for latent heat.

Using high-spatial-resolution snow data from the coupled global NCEP Climate Forecast System Reanalysis (CFSR), Zhiyan Zuo and colleagues found that the January–February–March (JFM) snow over high-latitude Eurasia has exhibited a negative trend over the past decades. The reduced Eurasian JFM snow corresponds to strengthened lower-tropospheric dry north-easterlies over south-eastern China and the surrounding oceans, resulting in decreased rainfall.

NCEP CFSv2 is becoming an important source of information for global and regional climate predictions. Retrospective forecasts by CFSv2 have been analysed and the system seems to be good at predicting variations of JFM Eurasian snow at least three months in advance, from year-to-year and over 10-year timescales. What's more, the CFSv2 successfully simulates the relationship between Eurasian snow and south-eastern China rainfall, as well as the associated atmospheric circulation patterns.

The authors now hope to understand why Eurasian snow patterns vary. For example, what are the effects of the North Atlantic sea-surface temperature, the North Atlantic Oscillation, the Arctic Oscillation and ENSO? How can the relationship between these effects and Eurasian snow be predicted in the CFSv2?

This work is reported in Environmental Research Letters (ERL).

(Environmental Research Web, 19/12/2011)