The difficulty to retrieve cloud condensation nuclei from space

All satellite-based estimates of aerosol cloud interactions used in IPCC's 5th assessment report rely on one assumption: that aerosol radiative properties from passive satellite remote sensing can serve as proxy for cloud condensation nuclei.

In this work, Philip uses the fully self-consistent global aerosol model ECHAM-HAM to show that this widely used assumption is violated for a large fraction of the Earth.

Figure: Map of correlation coefficients of surface CCN concentration with satellite retrievable column integrated aerosol optical depth. Note the extended areas of low or even negative correlations.

These results also demonstrate that vertically resolved aerosol radiative properties show significant potential in reducing these uncertainties. Previous attempts to address this research question based on in-situ measurements have been limited by the small number of available measurements and have provided limited authority for global aerosol-cloud interactions.

The global picture of the representativeness of aerosol radiative properties for cloud condensation nuclei developed in this study provides us with a new way to assess uncertainty in satellite based studies of aerosol cloud interactions.

Reference:

Stier, P.: Limitations of passive satellite remote sensing to constrain global cloud condensation nuclei, Atmos. Chem. Phys. Discuss., 15, 32607-32637, doi:10.5194/acpd-15-32607-2015, 2015.