School of GeoSciences

School of GeoSciences


Claire Bulgin - PhD Student, Edinburgh University

PhD - Quantifying Regional Aerosol Sources using Space-Borne Observations of Aerosol Optical Properties

Supervisors: Paul Palmer

                       Chris Merchant
                       Richard Siddans (Rutherford Appleton Laboratory) 
IPCC 2007: Radiative Forcing Components

Aerosols remain one of the largest uncertainties in radiative forcing.  Aerosol forcing is split into two components; direct and indirect effects (see IPCC figure).  Direct forcing includes scattering and absorption of both incoming and outgoing radiation and is the better understood of the two processes.  Indirect forcing relates to aerosols altering the microphysical properties of clouds.  The Twomey hypothesis (first indirect effect) states that aerosols act as cloud condensation nucei, increasing cloud droplet number, reducing cloud droplet size and consequently altering cloud albedo.  Extending this hypothesis, the Albrecht (second indirect) effect maintains that the reduction of cloud droplet size suppresses drizzle formation and increases cloud lifetime.

Aerosols have an atmsopheric lifetime in the region of a week.  Aerosol sources are diverse, including wind blown desert dust, sea salt, biogenic and industrial emissions.  This gives rise to large spatial and temporal variation in aerosol loading and composition, thus increasing the challenge of quantifying aerosol forcing globally.  Difficulties also arise in scaling up microphysical processes to accurately represent aerosol processes in global models.

Satellite data provides an opportunity to study aerosol indirect effects using retrievals of aerosol and cloud optical properties with global coverage.  My research to date focusses on quantifying the first indirect effect (see publication list).  My future interests include extending this anlaysis to look at the second indirect effect, and improving the representation of aerosols in GEOS-Chem, a global chemistry-transport model, through the use of data assimilation.


Bulgin, C. E., P. I. Palmer, G. E. Thomas, C. P. G. Arnold, D. Campmany, E. Carboni, R. G. Grainger, C. Poulsen, R. Siddans, and B. N. Lawrence, "Regional and seasonal variations of the Twomey indirect effect as observed by the ATSR-2 satellite instrument," Geophys. Res. Lett., accepted 2007