Articles | Volume 6, issue 5
Atmos. Meas. Tech., 6, 1287–1314, 2013

Special issue: Observations and modeling of aerosol and cloud properties...

Special issue: CHemistry and AeRosols Mediterranean EXperiments (ChArMEx)...

Atmos. Meas. Tech., 6, 1287–1314, 2013

Research article 17 May 2013

Research article | 17 May 2013

A 4-D climatology (1979–2009) of the monthly tropospheric aerosol optical depth distribution over the Mediterranean region from a comparative evaluation and blending of remote sensing and model products

P. Nabat1, S. Somot1, M. Mallet2, I. Chiapello3, J. J. Morcrette4, F. Solmon5, S. Szopa6, F. Dulac6, W. Collins7, S. Ghan8, L. W. Horowitz9, J. F. Lamarque10, Y. H. Lee11, V. Naik12, T. Nagashima13, D. Shindell11, and R. Skeie14 P. Nabat et al.
  • 1Météo-France, UMR3589, CNRS – CNRM-GAME, Centre National de Recherches Météorologiques, 42 avenue G. Coriolis, 31057 Toulouse cedex 1, France
  • 2Laboratoire d'Aérologie, UMR 5560, 16 avenue Édouard Belin, 31400 Toulouse, France
  • 3Laboratoire d'Optique Atmospérique, CNRS/Université Lille 1, UMR 8518, 59655 Villeneuve d'Ascq, France
  • 4European Centre for Medium-Range Weather Forecasts, Reading, UK
  • 5The Abdus Salam International Center for Theroretical Physics, Strada Costiera 11, 34100 Trieste, Italy
  • 6Laboratoire des Sciences du Climat et de l'Environnement, LSCE-IPSL, CEA-CNRS-UVSQ, 91191 Gif-sur-Yvette, France
  • 7Department of Meteorology, University of Reading, UK
  • 8Pacific Northwest National Laboratory, Richland, WA, USA
  • 9NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
  • 10NCAR Earth System Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 11NASA Goddard Institute for Space Studies and Columbia Earth Institute, New York, NY, USA
  • 12UCAR/NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
  • 13National Institute for Environmental Studies, Tsukuba, Japan
  • 14Center for International Climate and Environmental Research-Oslo (CICERO), Oslo, Norway

Abstract. Since the 1980s several spaceborne sensors have been used to retrieve the aerosol optical depth (AOD) over the Mediterranean region. In parallel, AOD climatologies coming from different numerical model simulations are now also available, permitting to distinguish the contribution of several aerosol types to the total AOD. In this work, we perform a comparative analysis of this unique multi-year database in terms of total AOD and of its apportionment by the five main aerosol types (soil dust, sea-salt, sulfate, black and organic carbon). We use 9 different satellite-derived monthly AOD products: NOAA/AVHRR, SeaWiFS (2 products), TERRA/MISR, TERRA/MODIS, AQUA/MODIS, ENVISAT/MERIS, PARASOL/POLDER and MSG/SEVIRI, as well as 3 more historical datasets: NIMBUS7/CZCS, TOMS (onboard NIMBUS7 and Earth-Probe) and METEOSAT/MVIRI. Monthly model datasets include the aerosol climatology from Tegen et al. (1997), the climate-chemistry models LMDz-OR-INCA and RegCM-4, the multi-model mean coming from the ACCMIP exercise, and the reanalyses GEMS and MACC. Ground-based Level-2 AERONET AOD observations from 47 stations around the basin are used here to evaluate the model and satellite data. The sensor MODIS (on AQUA and TERRA) has the best average AOD scores over this region, showing a relevant spatio-temporal variability and highlighting high dust loads over Northern Africa and the sea (spring and summer), and sulfate aerosols over continental Europe (summer). The comparison also shows limitations of certain datasets (especially MERIS and SeaWiFS standard products). Models reproduce the main patterns of the AOD variability over the basin. The MACC reanalysis is the closest to AERONET data, but appears to underestimate dust over Northern Africa, where RegCM-4 is found closer to MODIS thanks to its interactive scheme for dust emissions. The vertical dimension is also investigated using the CALIOP instrument. This study confirms differences of vertical distribution between dust aerosols showing a large vertical spread, and other continental and marine aerosols which are confined in the boundary layer. From this compilation, we propose a 4-D blended product from model and satellite data, consisting in monthly time series of 3-D aerosol distribution at a 50 km horizontal resolution over the Euro-Mediterranean marine and continental region for the 2003–2009 period. The product is based on the total AOD from AQUA/MODIS, apportioned into sulfates, black and organic carbon from the MACC reanalysis, and into dust and sea-salt aerosols from RegCM-4 simulations, which are distributed vertically based on CALIOP climatology. We extend the 2003–2009 reconstruction to the past up to 1979 using the 2003–2009 average and applying the decreasing trend in sulfate aerosols from LMDz-OR-INCA, whose AOD trends over Europe and the Mediterranean are median among the ACCMIP models. Finally optical properties of the different aerosol types in this region are proposed from Mie calculations so that this reconstruction can be included in regional climate models for aerosol radiative forcing and aerosol-climate studies.