Large-scale climate variability behind the wave energy extremes in the Yellow Sea during an unusual season

The Yellow Sea (YS) is exposed to various weather systems, such as typhoons, monsoon activities, and extratropical cyclones, which can pose  a major threat to the adjacent coastal regions through the development of powerful oceanic surface waves. Unusually severe surface wave events in the YS occur with considerable frequency during the boreal spring (March-April-May), but have received less attention compared to winter and summer. This study focuses on the characteristics of spring extreme wave events in the YS, based on observational and long-term reanalysis datasets. Our analysis shows that the extreme waves, defined as waves with a daily maximum height in the upper 5% of all springs, start to build up about 12 hours before the peak waves and continue for a longer period after the peak have been reached. During the extreme events, the Siberian High is found to extend anomalously eastward compared to spring climatology. Such an anomalous extension contributes to the increase of the sea level pressure gradient and the intensification of the surface wind speed in the YS. Meanwhile, in the range of 6~24 hours following the peaks of the extreme wave events in the YS, swells propagating from the far western North Pacific arrive in the YS. These swells from the western North Pacific, possibly generated by the same mesoscale system that has caused the extreme wave heights in the YS a few days in advance and has traveled northeastward, contribute to maintaining higher wave energy levels in the YS for longer after the atmospheric source has been removed. The large-scale environmental conditions can provide the predictability of extreme waves in the basin developed by these findings. Our analysis further reveals that more intense events tend to occur with eastward shift of the Siberian High, while the events occur more frequently with El Niños.  This study presents implications for assessing the risks associated with extreme waves in coastal regions and improving coastal management strategies in the YS.