The warm blob in the northeastern Pacific-the bridge leading to the 2015/16 El Niño


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Late in 2013 the sea became anomalously warm in the Gulf of Alaska. Known as the “warm blob”, these unusual conditions in the eastern North Pacific persisted for two years. At its peak, sea surface temperatures were 2.5 degrees higher than average (3-4 degrees in some specific regions). Down in the tropical Pacific Ocean, meanwhile, in late 2014 an El Niño began to brew. It pooled warm water off the coast of South America, and resulted in one of the strongest El Niños on record by 2015. The phenomenon persisted into early 2016.

So was the overlap of the warm blob and the 2015/16 super El Niño just pure coincidence? Most researchers believed that these two events were independent phenomena. Both extreme events draw a lot of media’s attention without clear conclusion (e.g., Godzilla El Nino Versus The BLOB: Who Will Win?). A new study led by Prof. Yu-heng Tseng at the Institute of Oceanography, National Taiwan University and his colleagues suggests that both are part of a larger Pacific-wide ocean-atmosphere coupling and are indeed connected (see the highlight news on the Environmental Research Web).

Their results showed a tight connection between sea surface temperature and atmospheric sea level pressure in the North Pacific. From early 2014 the North Pacific developed a temperature gradient, with negative sea surface temperature anomalies in the mid-latitude western Pacific, surrounded by positive anomalies in the eastern Pacific (extending from off California to the western Bering Sea), see Figure 1 below. Previous work has shown that such a pattern is known as the “Victoria Mode” and is forced by a basin-wide atmospheric ocean coupling. The coupling continues to evolve and intensify in 2015, finally leading to the development of 2015/16 super El Niño.

Prof. Tseng’s study shows that the warm blob was an intermediate step leading to the 2015/16 El Niño. Such events, more commonly observed after 2000, favour the development of El Niño but don’t guarantee its occurrence, showing that the events are linked, but that one does not directly cause the other. The linkages are complicated and related to other processes, but this enhanced understanding should help to predict El Niño variability better in the future. Further information about the associated mechanisms and details can be found in Prof. Tseng’s recent paper published in the Environmental Research Letters (Tseng et al., 2017).

Tseng, Y.H., Ding, R. and Huang, X.-M. (2017), “The warm blob in the northeastern Pacific-the bridge leading to the 2015/16 El Niño,” Environ. Res. Lett., 12, 054019.