Impact of Atmospheric Circulation and Meteorological Parameters on Wintertime Atmospheric Extinction in Chengdu and Chongqing of Southwest China during 2001–2016

Abstract

This study investigated the effect of atmospheric circulation and meteorological parameters on the surface atmospheric extinction coefficient (SEC) in Chengdu and Chongqing of southwest China during the winters of 2001–2016. Four predominant circulation types (CT) were first identified, representing a high-pressure system in the north (CT 1), a low-pressure system in the north (CT 2), a weak high-pressure system (CT 3) and a local low-pressure system (CT 4) at a geopotential height of 850 hPa. In Chengdu, variation in the SEC between the CTs was dominated by meteorological factors, such as wind, subsidence, inversion and planetary boundary layer height (PBLH), whereas the variation within each CT was mainly controlled by dispersion-related parameters (such as wind speed and PBLH for CTs 1, 2 and 4, which were associated with strong weather systems) or chemistry-related parameters (such as RH and T for CT 3, which was associated with a weak system). In Chongqing, dispersion and chemical processes were equally important due to the weaker impact of the atmospheric circulation. A new method for discriminating between synoptic and non-synoptic signals in SEC time series was proposed to estimate the effect of the circulation intensity by considering multiple influential meteorological parameters. Atmospheric circulation heightened the interannual SEC variations by ~23% in both Chengdu and Chongqing in more than half of the years but reduced them by 44.79% and 8.02% in Chengdu and Chongqing, respectively, in the remaining years. Synoptic changes were estimated to contribute 5–10% of the decreasing SEC trend but less than 1% of the increasing trend.