Interactions between aerosols and clouds are in good agreement between satellite data and climate models

Researcher Giulia Saponaro from the Finnish Meteorological Institute studied the properties of clouds and aerosols using remote sensing instruments and modelling tools in her doctoral dissertation in the Faculty of Science, University of Helsinki.

The MODerate Imaging Spectroradiometer (MODIS) is a useful tool for evaluating the capabilities and reliability of climate models, which are fundamental for investigating climate change. In her PhD research Giulia Saponaro determined potential improvements in the set-ups of three climate models by using MODIS as a reference dataset.

Giulia Saponaro investigated aerosol-cloud interaction from local, regional and global scale using ground-based and space-borne instruments and modelling tools.

Results on the local and regional scales show that contrasting aerosol backgrounds indicate a higher sensitivity of clouds to aerosol changes in cleaner ambient air. Lower sensitivity was found in polluted areas, further corroborating the notion that anthropogenic emissions modify clouds.

On the global scale, the estimates of the aerosol-cloud interactions present, overall, a good agreement between the satellite- and model-based values and are in line with results presented in literature.

“It was found that ground-based measurements of liquid clouds are in good agreement with MODIS cloud droplet size. Poor correlation was found in the amount of cloud liquid water due to the management of drizzle,” Saponaro says.

Combining data sources helps to answer open questions

The spaceborne sensor MODIS onboard the Earth Observing System Terra and Aqua platforms is a valuable tool in assessing the impact of atmospheric aerosol particles on clouds. They have been routinely gathering aerosol and cloud properties since 1999 and 2002, respectively, which were largely unattainable before the advent of MODIS.

Aerosol particles modify the optical and microphysical properties of clouds, consequently influencing climate by altering precipitation patterns, and the balance of incoming solar radiation and outgoing thermal radiation. Therefore, it is of crucial importance to improve our current level of understanding on the processes regulating the aerosol-cloud interactions.

“The scientific community should work towards the integration of different data sources, while accounting for their respective capabilities and limitations. This way, a robust and exhaustive response to any open questions regarding the effect of aerosol upon clouds can be obtained,” Saponaro says.

Public examination will be held on 8 January in Helsinki

Giulia Saponaro, M.Sc. will defend the doctoral dissertation entitled "Application of remotely-sensed cloud properties for climate studies" in the Faculty of Science, University of Helsinki, on 8 January 2020 at 12:00. The public examination will take place at the Finnish Meteorological Institute (Erik Palménin aukio 1, Helsinki).

Doctor Nicolas Bellouin, University of Reading, will serve as the opponent, and professor Veli-Matti Kerminen as the custos.

Further information

Giulia Saponaro, Finnish Meteorological Institute,, Twitter: @GiuliaSaponaro

The doctoral dissertation is available online in the University of Helsinki database Helda.