Potential impacts of Arctic warming on Northern Hemisphere mid-latitude aerosol optical depth.

The weather and climate conditions can provide favorable or unfavorable atmospheric background for the maintenance and development of haze events. This study investigates the potential impacts of Arctic warming on the variation of Northern Hemisphere mid-latitude aerosol optical depth (AOD) in winter when haze often occurs. We first analyze the spatio-temporal variability of wintertime AOD in mid-latitudes of Northern Hemisphere from NASA MERRA-2 for the period of 1980–2016 using the empirical orthogonal function analysis and morlet wavelet analysis. It showes increasing trend for AOD in East China and North India and decreasing trend for AOD in Europe and North America during last 37 years while inter-decadal fluctuations exist. In addition to the temporal trends of AOD, two long-term periodic variations with periods of about 7 and 11 years exist, which implies the potential impacts from natural variabilities. Further analysis shows high correlations between the mid-latitude winter AOD (WA) and Arctic summer (May and June) surface temperature (T₅₆). Moreover, the Arctic summer surface temperature demonstrates similar periodic variations with periods of about 7–9 and 11–13 years. Both of these indicate the potential impacts of Arctic summer warming on mid-latitude winter pollution. We then analyze the temporal correlations between Arctic summer temperature and mid-latitude winter AOD in different regions. Arctic T₅₆ correlates negatively with WA in Europe and North America, and positively with that in East Asia, North India and Middle East. Particularly, T₅₆ in western sea of Novaya Zemlya has the most prominent correlation with the WA in mid-latitudes of East Asia, especially in East China. This implies that Arctic T₅₆ in the Arctic circle of Europe could be used for rough estimates of winter AOD in East Asia. [ABSTRACT FROM AUTHOR]