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Abstract

Over the Far East in summer, climate is strongly influenced by the fluctuating Western Pacific Subtropical High (WPSH), and strong precipitation is often associated with southeasterly low-level wind that brings moist air from the southern China seas. The WPSH intraseasonal variability is partly influenced by quasi-stationary wave-trains propagating eastwards from Europe across Asia along the two westerly jets: the Silk-Road wave-train along the Asian jet at midlatitudes and the polar wave-train along the sub-polar jet. In the unusual summer of 2010, northeast China experienced its worst seasonal flooding for a decade, triggered by unusually severe precipitation. That summer was also characterized by a record-breaking heat wave over eastern Europe and Russia, whose impact on the precipitation further east over China has been little explored. Here, we examine the role of the Silk-Road and polar wave-trains, and their impact on precipitation over northeast China throughout August 2010, using station precipitation data and re-analyses. We found that there is a strong link between the Silk-Road wave-train and extreme precipitation events. Forecasting such regional precipitation events at the monthly time-scale remains a big challenge for operational global prediction systems. In this study, we use simulations with the atmospheric model of the European Centre for Medium-range Weather Forecasts (ECMWF) to highlight the key role of the Silk-Road and polar wave-trains in modulating extreme precipitation over north and northeast China in August 2010. While the ensemble-mean of the forecasts fails to predict the pulses of the Silk-Road wave-train, some model members show a high spatial correlation in upper-level meridional winds with re-analyses. Similarly, there is high spatial correlation between model meridional winds and precipitation. These results highlight the importance of better representing the intraseasonal evolution of the Silk-Road wave-train in order to improve the monthly prediction of summer precipitation over the Far East. © 2015 Royal Meteorological Society.