Aerosol radiative properties observed over M'Bour in Senegal during dry season - AMMA 2006 experiment
Abstract
The presented study was devoted to characterization of airborne aerosol optical properties and radiative effect on climate during the AMMA intensive experiment in M'Bour, Senegal, 2006. The outbreaks of biomass burning aerosols during the dry season occur on a background of frequent dust storms in the region. We analyzed several aerosol events that took place from January to March 2006, which allowed characterization of airborne mineral dust and mixture of biomass burning aerosols with dust. Climatology of key aerosol parameters for the analyzed dry season of the AMMA campaign showed high variability of aerosol sizes and spectral absorption, although aerosol loading was below the average. The LIDAR profiles imply two layers structure for aerosol mixing events and one layer for a dust event. We used atmospheric radiative transfer forward model employed in AERONET retrieval code for assessing aerosol radiative effect and efficiency of different aerosol types observed over the site. For example, the mixture of dust with small strongly absorbing particles yield aerosol radiative efficiency at the surface up to twice higher than of dust alone. In addition, we evaluated the importance of accounting for desert dust particle non-sphericity in simulation of aerosol radiative effects. Indeed, the non-spherical particle model employed in AERONET retrieval results in robust improvements in reproducing atmospheric radiances measured during desert dust events. In radiative forcing simulations the effects of particle non-sphericity are usually neglected. Our test showed that accounting for particle non-sphericity can be significant in the cases of the pronounced desert dust events where diffused radiation dominates in total downward flux. The measurements showed that for some dust episodes the diffused radiation contribution is at least 65 % of the total downward radiation during a day. For such situations the neglect of the aerosol particles non-sphericity can results in overestimations of instantaneous aerosol radiative effect at the surface by the value of 8 to 21 Wm-2 for AOD at 440 nm ranging from 0.5 to 2.0.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.A11A0048D
- Keywords:
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- 0305 Aerosols and particles (0345;
- 4801;
- 4906);
- 0360 Radiation: transmission and scattering