Warming effect of dust aerosols modulated by overlapping clouds below. (October 2017)

• Record Type: Journal Article
• Authors: Xu, Hui; Guo, Jianping; Wang, Yuan; Zhao, Chuanfeng; Zhang, Zhibo; Min, Min; Miao, Yucong; Liu, Huan; He, Jing; Zhou, Shunwu; Zhai, Panmao
• Is Part Of: Atmospheric environment. Volume 166(2017)
• Page Start: 393
• Page End: 402
• Publication Date: 2017-10
• Subjects: CALIPSO -- Cloud -- Dust aerosol -- Above-cloud dust aerosol -- Radiative forcing; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2017.07.036
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: Due to the substantial warming effect of dust aerosols overlying clouds and its poor representation in climate models, it is imperative to accurately quantify the direct radiative forcing (DRF) of above-cloud dust aerosols. When absorbing aerosol layers are located above clouds, the warming effect of aerosols strongly depends on the cloud macro- and micro-physical properties underneath, such as cloud optical depth and cloud fraction at visible wavelength. A larger aerosol-cloud overlap is believed to cause a larger warming effect of absorbing aerosols, but the influence of overlapping cloud fraction and cloud optical depth remains to be explored. In this study, the impact of overlapping cloud properties on the shortwave all-sky DRF due to springtime above-cloud dust aerosols is quantified over northern Pacific Ocean based on 10-year satellite measurements. On average, the DRF is roughly 0.62 Wm −2 . Furthermore, the warming effect of dust aerosols linearly increases with both overlapping cloud fraction and cloud optical depth. An increase of 1% in overlapping cloud fraction will amplify this warming effect by 1.11 Wm −2 τ −1 . For the springtime northern Pacific Ocean, top-of-atmosphere cooling by dust aerosols turns into warming when overlapping cloud fraction is beyond 0.20. The variation of critical cloud optical depth beyond which dust aerosols switch from exerting a net cooling to a net warming effect depends on the concurrent overlapping cloud fraction. When the overlapping cloud coverage range increases from 0.2 to –0.4 to 0.6–0.8, the corresponding critical cloud optical depth reduces from 6.92 to 1.16. Our results demonstrate the importance of overlapping cloud properties for determining the springtime warming effect of dust aerosols. Highlights: In spring, frequency of above-cloud dust aerosols over northern Pacific Ocean is high up to 0.12. The springtime warming effect of above-cloud dust aerosols increases with overlapping cloud fraction and cloud optical depth. The critical cloud optical depth for dust effect depends on the concurrent overlapping cloud fraction.