Abstract
The possible influence of the Atlantic multidecadal oscillation (AMO) and the Pacific decadal oscillation (PDO) on the meteorological conditions associated with haze over central eastern China at decadal time scale was investigated using reanalysis and observational dataset for 1979–2018. Four indices, including Siberian high (SH) strength and position indices (SHI/SHPI), a normalized near-surface wind-speed index (WSI) and a potential air temperature gradient index (ATGI), are adopted to denote the meteorological conditions associated with haze. Results shown that the AMO and PDO are both highly correlated with the fluctuation of meteorological factors associated with haze on decadal scale. Although AMO and PDO were in opposite phases during the whole period, since 1997, they both changed phases (AMO shifted to a positive phase and PDO changed to negative) and became favorable for an anomalous dipole-type SLP pattern in the middle-high latitudes of East Asia. The AMO has played a leading role in decadal variation of the large-scale circulation system, while the PDO has had a closer relationship with the lower ventilation condition in eastern China. On the decadal time scale, the AMO stimulates a zonal teleconnection wave train (the AMO northern Hemisphere pattern, ANH) that originates from the North Atlantic Ocean and passes through central Europe, the northern Ural Mountains, Lake Balkhash-Baikal, and central eastern China. During the positive phase of AMO, the ANH induces a stronger and westward shifted SH, with the central eastern China controlled by the anomalous high pressure. In addition, affected by the cyclone (anticyclone) anomaly over Hetao region and North China (the Sea of Japan), southerly wind anomalies dominate over central eastern China. Compared with the AMO, the wave train generated by the negative (positive) PDO phase mainly propagates in the Pacific region, and there is a strong anticyclonic (cyclonic) anomaly over the Northeast Pacific, guiding the air flow southward (northward) along the East Asian coast and thus suppressing (encouraging) the dispersion of pollutants and resulting in above (below)-normal haze episodes.
Highlights
In past few decades, the occurrence of air pollution in winter has increased significantly with the explosive growth of China’s economy
Using observation and reanalysis datasets, we first analyzed the relationships of the sea level pressure (SLP), wind speed, and low-level potential air temperature gradient in eastern East Asia with the Atlantic multidecadal oscillation (AMO) and Pacific decadal oscillation (PDO) during the winters in the 1979–2018 period
By analyzing the teleconnection wave train and wave energy propagation excited by the AMO and PDO respectively, we further explored the possible impact of ocean signals on these meteorological factors in winter and their differences
Summary
The occurrence of air pollution in winter has increased significantly with the explosive growth of China’s economy. Further analysis of a persistent and severe haze outbreak in eastern China in January 2013 demonstrated that the SHI could not fully describe the impact of SH variation in winter; the aforementioned haze episode was associated with an anomalous eastward extension of the SH. On this basis, they proposed a new indicator, the SH position index (SHPI), depicting the mean longitudinal position of the SH and reflecting the large-scale wind fields that control pollutant transportation and transformation in China
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