On the connection between interannual variations of winter haze frequency over Beijing and different ENSO flavors.

This study investigated the connection between interannual variations in winter haze frequency over Beijing and different flavors of the El Niño-Southern Oscillation (ENSO). The results showed that the haze frequency was highest during eastern-Pacific (EP) El Niño winters and lowest during EP La Niña winters. No below-normal winter haze frequency years were observed during EP El Niño winters, and no above-normal years were observed during EP La Niña winters. However, the relationship between winter haze frequency and central-Pacific (CP) ENSO conditions was more complex, i.e., both above- and below-normal haze frequency years were equally probable during CP El Niño and CP La Niña winters, and the difference in the number of mean haze days associated with these flavors was exceptionally small. The nearly opposite atmospheric circulation patterns between EP El Niño and EP La Niña winters were responsible for the substantial difference in local winter haze frequency, as these patterns established favorable and unfavorable local meteorological conditions for haze formation, respectively. However, the diverse in situ haze frequency situations during CP El Niño and CP La Niña winters and the small relative differences between such winters could reflect the complexity of the CP ENSO's impacts on haze-related circulation anomalies. The results of this study may help improve winter haze frequency forecasts for Beijing through more accurate climatic predictions.