Overview of the Chemistry-Aerosol Mediterranean Experiment/Aerosol Direct Radiative Forcing on the Mediterranean Climate (ChArMEx/ADRIMED) summer 2013 campaign

Abstract

Abstract. The Chemistry-Aerosol Mediterranean Experiment (ChArMEx; http://charmex.lsce.ipsl.fr) is a collaborative research program federating international activities to investigate Mediterranean regional chemistry-climate interactions. A special observing period (SOP-1a) including intensive airborne measurements was performed in the framework of the Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region (ADRIMED) project during the Mediterranean dry season over the western and central Mediterranean basins, with a focus on aerosol-radiation measurements and their modeling. The SOP-1a took place from 11 June to 5 July 2013. Airborne measurements were made by both the ATR-42 and F-20 French research aircraft operated from Sardinia (Italy) and instrumented for in situ and remote-sensing measurements, respectively, and by sounding and drifting balloons, launched in Minorca. The experimental setup also involved several ground-based measurement sites on islands including two ground-based reference stations in Corsica and Lampedusa and secondary monitoring sites in Minorca and Sicily. Additional measurements including lidar profiling were also performed on alert during aircraft operations at EARLINET/ACTRIS stations at Granada and Barcelona in Spain, and in southern Italy. Remote-sensing aerosol products from satellites (MSG/SEVIRI, MODIS) and from the AERONET/PHOTONS network were also used. Dedicated meso-scale and regional modeling experiments were performed in relation to this observational effort. We provide here an overview of the different surface and aircraft observations deployed during the ChArMEx/ADRIMED period and of associated modeling studies together with an analysis of the synoptic conditions that determined the aerosol emission and transport. Meteorological conditions observed during this campaign (moderate temperatures and southern flows) were not favorable to producing high levels of atmospheric pollutants or intense biomass burning events in the region. However, numerous mineral dust plumes were observed during the campaign, with the main sources located in Morocco, Algeria and Tunisia, leading to aerosol optical depth (AOD) values ranging between 0.2 and 0.6 (at 440 nm) over the western and central Mediterranean basins. One important point of this experiment concerns the direct observations of aerosol extinction onboard the ATR-42, using the CAPS system, showing local maxima reaching up to 150 M m −1 within the dust plume. Non-negligible aerosol extinction (about 50 M m −1 ) has also been observed within the marine boundary layer (MBL). By combining the ATR-42 extinction coefficient observations with absorption and scattering measurements, we performed a complete optical closure revealing excellent agreement with estimated optical properties. This additional information on extinction properties has allowed calculation of the dust single scattering albedo (SSA) with a high level of confidence over the western Mediterranean. Our results show a moderate variability from 0....

In situ measurements of desert dust particles above the western Mediterranean Sea with the balloon-borne Light Optical Aerosol Counter/sizer (LOAC) during the ChArMEx campaign of summer 2013

“…To perform the comparison with CALIOP aerosol extinction data, the LOAC aerosol extinctions are calculated at 532 nm from the measured size distribution using the mineral dust refractive index as presented above Finally, we use the aerosol measurements obtained during an ATR-42 aircraft flight close to Minorca. The instrumentation installed on board the aircraft is described in detail in Denjean et al (2016). The aerosol size distribution was determined from an optical particle counter GRIMM 1.129 (nominal size range 0.25-32 µm), an ultra-high sensitivity aerosol spectrometer (UHSAS; 0.04-1 µm), and a forward- scattering spectrometer probe FSSP-300 (0.28-20 µm).…”

“…The refractive index was set to 1.53 − i0.0025, which corresponds to the mean value determined by Denjean et al (2016) for the Saharan dust plume events documented during the summer 2013 ChArMEx campaign. This approach suffers from four approximations: (i) all counted particles are assumed to be mineral dust; (ii) the contribution of the smallest particles is unknown, leading to some underestimation of the calculated aerosol extinctions; (iii) the grains are considered as spherical while they are not; and (iv) the refractive index of the grains is not always well-known.…”

“…The observations were conducted during the dry season over the western and central Mediterranean basins. During the first special observation period (SOP) entitled Aerosol Direct Radiative Forcing on the Mediterranean Climate (ChArMEx/ADRIMED SOP-1A) from mid-June to early July, the focus was on aerosol-radiation measurements and their modelling (Mallet et al, 2016). During the second SOP entitled Secondary Aerosol Formation in the Mediterranean (ChArMEx/SAFMED SOP-1B) from mid-July to early August, the focus was on atmospheric chemistry (Zannoni et al, 2017).…”

“…Some aircraft observations were also conducted in situ inside dust plumes, but they are expensive and scarce (e.g. Schmid et al, 2000;Dulac and Chazette, 2003;Haywood et al, 2003;Reid et al, 2003a;Formenti et al, 2008;Weinzierl et al, 2009Weinzierl et al, , 2011Chen et al, 2011;Denjean et al, 2016), and were often limited to several micrometres in terms of the particle size range covered and did not explore the same dust plume along its transport. One of the incompletely resolved issues is the evolution of the dust particle size distribution during long-range transport .…”

“…Within the project, a large regional field campaign was performed from mid-June to early August 2013 with intensive airborne measurements including in situ balloon-borne aerosol (Mallet et al, 2016) and ozone measurements. The observations were conducted during the dry season over the western and central Mediterranean basins.…”