Links of climate variability in Arctic sea ice, Eurasian teleconnection pattern and summer surface ozone pollution in North China

Summer surface O3 pollution has rapidly intensified in China in the recent decade, damaging human and ecosystem health. In 2017, the summer mean maximum daily average 8 h concentration of ozone was greater than 150 µg m−3 in North China. Based on the close relationships between the O3 concentration and the meteorological conditions, a daily surface O3 weather index was constructed, which extends the study period to the historical period before 2007 and the projected future. Here, we show that in addition to anthropogenic emissions, the Eurasian teleconnection pattern (EU), a major globally atmospheric teleconnection pattern, influences surface O3 pollution in North China on a timescale of climate. The local meteorological conditions associated with the EU positive phase supported intense and efficient photochemical reactions to produce more surface O3. The associated southerlies over North China transported surrounding O3 precursors to superpose local emissions. Increased solar radiation and high temperatures during the positive EU phase dramatically enhanced O3 production. Furthermore, due to the close connection between the preceding May Arctic sea ice (SI) and summer EU pattern, approximately 60 % of the interannual variability in O3-related weather conditions was attributed to Arctic sea ice to the north of Eurasia. This finding will aid in understanding the interannual variation in O3 pollution, specifically the related meteorological conditions.

Impact of the Eurasian Teleconnection on the Interannual Variability of Haze-Fog in Northern China in January

Using meteorological observation data and NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data, the impacts of the atmospheric circulation pattern on the interannual variability of haze-fog in northern China in January are studied by means of statistical methods. The results showed that the Eurasian teleconnection (EU) at the 500 hPa isostatic surface is the most important pattern affecting the haze-fog frequency in northern China. However, the existing EU index cannot perfectly describe this pattern. To this end, this study selects three main activity centers to define a new EU index, which are located in the Europe (10 °E, 55 °N), Siberia (80 °E, 60 °N), and Shandong, China (120 °E, 40 °N). The difference between the existing EU index and the new EU index is mainly the position of the anomaly center of the 500 hPa geopotential height. The EU is in a negative phase in higher haze-fog years but is in a positive phase in lower haze-fog years. The 500 hPa geopotential height shows negative anomalies in Europe and East Asian and a positive anomaly in Siberia in the negative EU phase. Using Plumb wave activity flux analysis, it was found that the cold wave affecting northern China is less in the negative EU phase than that in the positive EU phase, which resulted in more haze-fog days. In addition, the results also showed that the EU pattern goes through a considerable development and decay within 13 days. The visibility starts to significantly decrease at a lag of −1 to 2 days in the negative EU peak phase and is influenced by the weak north wind that is caused by the high pressure.

Teleconnection between Summer NAO and East China Rainfall Variations: A Bridge Effect of the Tibetan Plateau

Although the impact of the North Atlantic Oscillation (NAO), especially the antecedent NAO in winter and spring, on East Asian summer climate has been studied extensively, the possible connection from the summer NAO (SNAO) and then the Tibetan Plateau (TP) to East China summer rainfall remains unclear. This study reveals that on interannual time scales the SNAO is significantly correlated with the variations of East China summer rainfall and the thermal forcing of the TP provides an intermediate bridge effect in this Eurasian teleconnection. The SNAO primarily regulates the rainfall variability over the TP through large-scale wave trains and the TP rainfall anomalies in turn lead to a change in local diabatic heating, which excites Rossby waves to the downstream regions. To the northeast of the TP, an anomalous barotropic cyclone is formed in the nearly entire troposphere, generating low-level northerly flow anomalies over northern China. Meanwhile, the TP heating also induces low-level southerly flow anomalies over southern China. The anomalous northerly and southerly winds converge in the lower troposphere, enhancing the summer rainfall over central East China. Compared to the SNAO, the TP thermal forcing exerts a more direct impact on the variations of East China summer rainfall in the Eurasian teleconnection discussed.