New Publication: Cloud fraction mediates the aerosol optical depth – cloud top height relationship

Gryspeerdt, E., Stier, P., Grandey, B. S. (2014) Cloud fraction mediates the aerosol optical depth – cloud top height relationship Geophysical Research Letters DOI 10.1002/2014GL059524

Abstract

The observed strong link between aerosol optical depth (τ) and cloud top pressure (ptop) has frequently been interpreted as the invigoration of convective clouds by aerosol, with increased τ being strongly correlated with decreases in ptop (increases in cloud top height). A strong correlation between τ and cloud fraction (fc) has also been observed. Using satellite-retrieved data, here we show that ptop is also strongly correlated to fc, and when combined with the strong sensitivity between fc and τ, a large proportion of the relationship between ptop and τ can be reconstructed. Given the uncertainties about the influence of aerosol-cloud interactions on the τ − fc relationship, this suggests that a large fraction of the τ − ptop correlation may not be due to aerosol effects. Influences such as aerosol humidification and meteorology play an important role and should therefore be considered in studies of aerosol-cloud interactions.