Calendar Event Details
AEROCENTER: Antti Arola
Affiliation: Finnish Meteorological Institute, Kuopio, Finland
Event Date: Tuesday, September 23, 2014
Location: G133
Time: 11:00 AM
On the use of AERONET measurements to better constrain the aerosol direct radiative effect
The diurnal variability of aerosol optical depth (AOD) can be significant, depending on location and dominant aerosol type. However, these diurnal cycles have rarely been taken into account in measurement-based estimates of aerosol direct radiative forcing (ADRF) or aerosol direct radiative effect (ADRE). The objective of our study was to estimate the influence of diurnal aerosol variability at the top of the atmosphere ADRE estimates. By including all the possible AERONET sites, we wanted to assess the influence on global ADRE estimates. While focusing also in more detail on some selected sites of strongest impact, our goal was to also see the possible impact regionally. We calculated ADRE with different assumptions about the daily AOD variability: taking the observed daily AOD cycle into account and assuming diurnally constant AOD. Moreover, we estimated the corresponding differences in ADREs, if the single AOD value for the daily mean was taken from the the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra or Aqua overpass times, instead of accounting for the true observed daily variability. This study was published in Arola et al. 2013.
The AERONET provides aerosol size distributions and complex refractive index at four wavelengths (440, 675, 870, and 1020 nm). This information is used to retrieve the relative proportions of brown carbon BrC, black carbon BC, mineral dust and scattering host, separately for fine and coarse modes. The retrieval method is extended from Schuster et al. 2005 and Arola et al. 2011. Our objective has been to estimate the aerosol direct radiative effect of BrC by using these volume fractions of BrC from all available AERONET sites. The effect of BrC at TOA has been estimated as the difference between net fluxes for all aerosols and non-BrC aerosols using the radiative transfer package libRadtran. The ultimate goal is to estimate the global BrC radiative effect, therefore additionally results from global aerosol model is needed to estimate the effect from regions remote to AERONET sites (e.g. large ocean areas). Therefore, we have started also a work aiming to produce new AERONET based estimates for BrC emissions that we can use in our global aerosol model. We use these same retrievals of BrC concentrations from AERONET data, but in this case to estimate the fraction of BrC emissions from the total organic carbon (OC) emissions, using an iteration tool based on a Kalman filter. With this tool we optimize the the BrC emission fractions for different emissions sources (biomass burning, fossil fuel, and biogenic emissions) in ECHAM6-HAM model. This is on-going work, but I will show some results obtained so far.
References
Arola, A., Schuster, G., Myhre, G., Kazadzis, S., Dey, S., and Tripathi, S. N.: Inferring absorbing organic carbon content from AERONET data, Atmos. Chem. Phys., 11, 215-225, doi:10.5194/acp-11-215-2011, 2011.
Arola, A., Eck, T.F., Huttunen, J., Lehtinen, K.E.J., Lindfors, A.V., Myhre, G., Smirnov, A., Tripathi, S.N., and Yu, H.: Influence of observed diurnal cycles of aerosol optical depth on aerosol direct radiative effect, Atmos. Chem. Phys., 13, 7895-7901, doi:10.5194/acp-13-7895-2013, 2013.
Schuster, G. L., O. Dubovik, B. N. Holben, and E. E. Clothiaux (2005), Inferring black carbon content and specific absorption from Aerosol Robotic Network (AERONET) aerosol retrievals, J. Geophys. Res., 110, D10S17, doi:10.1029/2004JD004548.
Posted or updated: Wednesday, September 10, 2014
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