Regional strong winter wind events over Beijing-Tianjin-Hebei and the corresponding weather patterns during 1979—2018

Changes of strong winter wind events in the Beijing-Tianjin-Hebei mega-region and corresponding weather circulation patterns were revealed with analysis of the daily wind speed at various meteorological stations and ERA-Interim reanalysis, for the winter season from 1979-2018. A total of 285 regional strong wind days were counted, frequency of strong windy days was found to have decreased significantly with a trend of −0.96 d·(10 a)⁻¹(P<0.05). Large-scale circulation associated with strong wind events in winter could be classified into two patterns by hierarchical clustering based on daily 500 hPa geopotential height anomalies. The two weather patterns accounted for strong winds for 110 and 175 d, respectively. Composite-analysis was found to demonstrat alternatively positive and negative anomalies west-east oriented over Eurasia. China is under the control of anomalous low pressure in the middle and lower troposphere, accompanied with anomalous strong northerly wind and low temperature near ground. For the first clustering type, circulation anomalies appeared in western Eurasia and disappeared in northwestern Pacific, lasting approximately 15 d. Lifetime was approximately 18 d for the second clustering types. Frequency of the first type decreased significantly at a rate of −0.72 d·(10 a)⁻¹(P<0.01). For the second, decrease rate was −0.23 d·(10 a)⁻¹ (P<0.5). These data suggest that observed decrease in regional strong wind events might be largely due to rapid reduction of the first weather type.