Effects of Biomass Burning on Stratocumulus Droplet Characteristics, Drizzle Rate, and Composition. Issue 22 (28th November 2019)

• Record Type: Journal Article
• Authors: Hossein Mardi, Ali; Dadashazar, Hossein; MacDonald, Alexander B.; Crosbie, Ewan; Coggon, Matthew M.; Azadi Aghdam, Mojtaba; Woods, Roy K.; Jonsson, Haflidi H.; Flagan, Richard C.; Seinfeld, John H.; Sorooshian, Armin
• Is Part Of: Journal of geophysical research. Volume 124:Issue 22(2019)
• Page Start: 12301
• Page End: 12318
• Publication Date: 2019-11-28
• Subjects: Biomass Burning -- Stratocumulus -- Aerosol -- Cloud -- EVS‐3 -- ACTIVATE; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2019JD031159
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: This study reports on airborne measurements of stratocumulus cloud properties under varying degrees of influence from biomass burning (BB) plumes off the California coast. Data are reported from five total airborne campaigns based in Marina, California, with two of them including influence from wildfires in different areas along the coast of the western United States. The results indicate that subcloud cloud condensation nuclei number concentration and mass concentrations of important aerosol species (organics, sulfate, nitrate) were better correlated with cloud droplet number concentration ( N d ) as compared to respective above‐cloud aerosol data. Given that the majority of BB particles resided above cloud tops, this is an important consideration for future work in the region as the data indicate that the subcloud BB particles likely were entrained from the free troposphere. Lower cloud condensation nuclei activation fractions were observed for BB‐impacted clouds as compared to non‐BB clouds due, at least partly, to less hygroscopic aerosols. Relationships between N d and either droplet effective radius or drizzle rate are preserved regardless of BB influence, indicative of how parameterizations can exhibit consistent skill for varying degrees of BB influence as long as N d is known. Lastly, the composition of both droplet residual particles and cloud water changed significantly when clouds were impacted by BB plumes, with differences observed for different fire sources stemming largely from effects of plume aging time and dust influence. Key Points: Primary activation of sub‐cloud CCN was the key driver of cloud droplet concentration (Nd ) in biomass burning (BB) and non‐BB conditions Relationships between Nd and either droplet effective radius (re ) or rain rate (R) are similar regardless of the level of BB influence Cloud water and droplet residual particle composition differed between BB and non‐BB conditions