Effects of solid aerosols on partially glaciated clouds

• Published in: Quarterly journal of the Royal Meteorological Society Vol. 144; no. 717; pp. 2634 - 2649
• Main Authors: Kudzotsa, Innocent, Phillips, Vaughan. T. J., Dobbie, Steven
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-10-2018; Wiley Subscription Services, Inc; Wiley Blackwell (John Wiley & Sons)
• Subjects: Aerosol concentrations; Aerosol effects; Aerosols; aerosol–cloud interactions; cloud microphysics; cloud-resolving models; Clouds; Convection; Convective clouds; Earth and Related Environmental Sciences; Geovetenskap och miljövetenskap; glaciated clouds; Ice nuclei; indirect effects; Meteorologi och atmosfärforskning; Meteorological satellites; Meteorology and Atmospheric Sciences; Natural Sciences; Naturvetenskap; Nucleus; Optical thickness; Stratiform clouds; Tropical climate; Updraft
• ISSN: 0035-9009; 1477-870X
• DOI: 10.1002/qj.3376

Sensitivity tests were conducted using a state‐of‐the‐art aerosol–cloud to investigate the key microphysical and dynamical mechanisms by which solid aerosols affect glaciated clouds. The tests involved simulations of two contrasting cases of deep convection—a tropical maritime case and a midlatitude continental case, in which solid aerosol concentrations were increased from their pre‐industrial (1850) to their present‐day (2010) levels. In the midlatitude continental case, the boosting of the number concentrations of solid aerosols weakened the updrafts in deep convective clouds, resulting in reduced snow and graupel production. Consequently, the cloud fraction and the cloud optical thickness increased with increasing ice nuclei (IN), causing a negative radiative flux change at the top of the atmosphere (TOA), that is, a cooling effect of −1.96 ± 0.29 W/m2. On the other hand, in the tropical maritime case, increased ice nuclei invigorated upper‐tropospheric updrafts in both deep convective and stratiform clouds, causing cloud tops to shift upwards. Snow production was also intensified, resulting in reduced cloud fraction and cloud optical thickness, hence a positive radiative flux change at the TOA—a warming effect of 1.02 ± 0.36 W/m2 was predicted.
The glaciation aerosol indirect effect arising from increasing solid aerosol concentrations in (a) CLASIC and (b) TWPICE. Meanings of abbreviations: GC‐AIE = glaciated clouds AIE, GCL‐AIE = glaciated clouds lifetime AIE, GCAE‐AIE = glaciated clouds albedo‐emissivity AIE.
Solid aerosols exhibited contrasting effects between continental and maritime clouds. In continental clouds, the boosting of solid aerosol concentrations weakened the updrafts in deep convection, resulting in reduced snow and graupel production. Consequently, the fraction and the optical thickness of clouds increased, causing cloud brightening. While in maritime clouds, increased ice nuclei invigorated the upper‐tropospheric updrafts, which pushed cloud tops upwards and intensified snow production. This caused a warming effect by reducing the fraction and the optical thickness of clouds.