Dr Florent Malavelle

Summary of current research:

Terrestrial carbon production is intimately tied to the supply of solar radiation in a subset of the visible portion of the electromagnetic radiation called the Photo-synthetically Active Radiation (PAR). Solar radiation in sufficient intensity and duration is critical for plant growth. If any decrease in solar radiation is accompanied by an increase in the component of diffuse radiation, plant productivity can increase due to a more efficient production per unit of PAR. This is also known as the diffuse light fertilization effect.

Biomass burning smoke from deforestation and the burning of agricultural waste emit a complex cocktail of aerosol particles which can exert significant impacts on climate through their direct, semi-direct and indirect effects. In addition to these effects which are relatively well established, biomass burning aerosols can increase the proportion of diffuse radiation at the surface of the Earth which can increase the effective photosynthesis of plant canopies, enhancing growth, carbon storage and reducing atmospheric concentrations of CO₂

The aim of this research consist in implementing parameterisations of the impact of diffuse and direct radiation upon photosynthesis rates and net primary productivity in the biosphere within a fully coupled Earth System climate Model framework (UKMO-HadGEM2-ES) and use the parameterisations in multicentennial simulations of the Earth’s climate.

This research is conducted within the South AMerican Biomass Burning Analysis - SAMBBA project – which aims to investigate the properties of biomass burning pollution over South America, and assess its impact on weather, air quality, climate and biosphere feedbacks.

Summary of previous research 2011-2013:

The planetary albedo is strongly affected by clouds. In the frame of the climate change, there is a large uncertainty associated with the aerosols effects on planetary albedo and radiative forcing. However, an even larger uncertainty due to the effects of aerosols particles on cloud albedo and radiative forcing remains. Despite recent improvements in Global Climate Models (GCM) and Earth System Models (ESM), Aerosol-Cloud Interactions (ACI) are poorly understood and constrained, hence highly uncertain.

Aerosol particles or that component that act as Cloud Condensation Nuclei (CCN) are an essential ingredient for the formation of clouds. The microphysical link between the two comes through the process of droplet activation which is a strong function of the cloud-scale updraft velocity. A positive vertical velocity will lead to an adiabatic cooling associated with an increase in relative humidity. If the relative humidity exceeds 100%, i.e. the parcel is supersaturated, CCNs can activate and grow to form cloud droplets.

Physically based parametrisations that predict number of activated CCN as a function of aerosol properties (size, number and composition) and vertical velocity have been developed and implemented in GCMs. These parametrisations are sensitive to updraft velocity which poses a problem because the sub-cloud velocity which controls activation can occur at smaller scales than the grid of models. Hence, a pre-requisite for a more robust representation of ACI in models is to constrain the sub-grid scale variability of updraft velocity.

This research was part of the ACID-PRUF programme which aims to reduce the uncertainty in the radiative forcing associated with the cloud-aerosol interaction.

PhD in Atmospheric Sciences at Université de Toulouse, France (2008-2011). Direct and semi-direct radiative effects of dust and biomass burning aerosols and their climatic impacts on a regional scale over West Africa.

Contact: f.malavelle@exeter ; florent.malavelle@metoffice.gov.uk +44(0)1392 886612