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Beijing Climate Center: La Nina conditions come to an end

Source:China Meteorological News Press08-02-2017

Since entering La Nina conditions on August 2016, the cold sea temperature in central-eastern equatorial Pacific remains stable. While after autumn, the cold sea temperature is characterized by a contracted scope and a weaker intensity. From November 2016 to January 2017, Nino3.4 sea surface temperature anomaly index has constantly ramped up. According to the latest monitoring results of Beijing Climate Centre (BCC), average sea temperature index in January 2017 registered -0.33℃, up by 0.09℃ compared with the figure in December (-0.42℃). Therefore, in accordance with the latest ENSO monitoring criteria of China Meteorological Administration (CMA), 3-month running average value of December recorded -0.43℃. As a result, La Nina conditions only lasted 4 months, not constituting a formal La Nina event.

The driving force of La Nina is trade wind and the cold water. Trade wind blows large amount of warm water to western equatorial Pacific. When the warm water in eastern equatorial Pacific is blown away, it will be replenished by the cold water under the sea surface. When trade wind gains intensity, upturning of deep water in East Pacific will strengthen and the sea surface temperature will be abnormally low. Therefore, the atmospheric pressure in eastern equatorial Pacific will descend and atmospheric pressure in the west will ascend, which facilitates the gaining momentum of trade wind and the formation of La Nina.

Dr. Zhou Bing, chief expert from BCC held the view that the driving force of this winter La Nina is not strong enough. And another contributor for the sluggish La Nina is global warming. The warming trend of global sea surface temperature is pronounced, which is adverse to cold water event. As a consequence, in recent years La Nina Event has been inconsistent with El Nino. This winter China has experienced abnormally warm conditions. This phenomenon is mainly attributable to the weak eastern Asian monsoon and fewer cold weather processes.

The latest week Nino3.4 index was recorded -0.3℃. The scope of anomalous cold sea temperature in central-eastern equatorial Pacific has further dwindled. It is predicted that from the winter in 2017 to this spring, central-eastern equatorial Pacific will sustain the normal state. Noticeably, different countries or institutions have adopted diverse data analysis to access myriad results. BCC follows closely the sea temperature change in central-eastern equatorial Pacific and will timely provide the updated monitoring. (Feb, 8)

Reporter: Sun Nan, Huang Zili

Editor: Liu Shuqiao