Aerosol properties above clouds over the South East Atlantic Ocean during the fire season: comparison between observations from POLDER/PARASOL and AeroCom models
Abstract
The estimation of the aerosol radiative impact by climate models is especially challenging in the presence of clouds, not only because of the variety and the complexity of the interaction processes, but also because of the variability of cloud and aerosol properties [Boucher et al., 2013; Myhre et al., 2013]. The South East Atlantic Ocean is a good testbed for the representation of aerosols in cloudy skies by climate models. During the fire season, absorbing biomass burning aerosols from Southern Africa are frequently observed above the semi-permanent low cloud layer. Recent studies based on satellite observations have highlighted the strong Direct Radiative Effect (DRE) typically associated with these aerosols, which can reach instantaneous values larger than +130W.m-2 [DeGraaf et al., 2012; Peers et al., 2015]. Within the AeroCom models, important discrepancies have been observed on both the magnitude and the sign of the DRE over the South East Atlantic Ocean. In order to understand these differences and to constrain models, observations of aerosol and cloud properties are needed. An original method has been developed to retrieve the key parameters for the estimation of the DRE of aerosol above clouds using satellite observations from POLDER/PARASOL: the Above-Cloud Aerosol Optical Thickness (ACAOT), their Single Scattering Albedo (ACSSA) and the cloud optical thickness [Waquet et al., 2013a & 2013b; Peers et al., 2015]. The aerosol properties observed over the South East Atlantic Ocean for the fire season 2006 have been compared to 5 AeroCom models [Peers et al., 2016]: GOCART, HadGEM3, ECHAM5-HAM2, OsloCTM2 and SPRINTARS. This analysis has revealed that most models do not reproduce the large aerosol load episodes observed by POLDER, which is likely due to the vertical transport calibration and lower aerosol injection height. In addition, POLDER ACSSA is best reproduced by models with a high imaginary part of the black carbon refractive index, in accordance with recent recommendations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.A41D0071P
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3305 Climate change and variability;
- ATMOSPHERIC PROCESSESDE: 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSESDE: 3360 Remote sensing;
- ATMOSPHERIC PROCESSES