Overview of the Chemistry-Aerosol Mediterranean Experiment/Aerosol Direct Radiative Forcing on the Mediterranean Climate (ChArMEx/ADRIMED) summer 2013 campaign
The Chemistry-Aerosol Mediterranean Experiment (ChArMEx; <a href="http://charmex.lsce.ipsl.fr" target="_blank">http://charmex.lsce.ipsl.fr</a>) is a collaborative research program federating international activities to investigate Mediterranean regional chemistry-...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/455/2016/acp-16-455-2016.pdf |
| Summary: | The Chemistry-Aerosol
Mediterranean Experiment (ChArMEx;
<a href="http://charmex.lsce.ipsl.fr" target="_blank">http://charmex.lsce.ipsl.fr</a>) 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<sup>−1</sup> within the
dust plume. Non-negligible aerosol extinction (about 50 M m<sup>−1</sup>)
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 0.90 to 1.00 (at 530 nm)
for all flights studied compared to that reported in the literature on this
optical parameter. Our results underline also a relatively low difference in
SSA with values derived near dust sources. In parallel, active remote-sensing
observations from the surface and onboard the F-20 aircraft suggest a complex
vertical structure of particles and distinct aerosol layers with sea spray
and pollution located within the MBL, and mineral dust and/or aged North
American smoke particles located above (up to 6–7 km in altitude).
Aircraft and balloon-borne observations allow one to investigate the vertical
structure of the aerosol size distribution showing particles characterized by a
large size (> 10 µm in diameter) within dust plumes. In most of
cases, a coarse mode characterized by an effective diameter ranging between 5
and 10 µm, has been detected above the MBL. In terms of shortwave
(SW) direct forcing, in situ surface and aircraft observations have been merged
and used as inputs in 1-D radiative transfer codes for calculating the aerosol direct
radiative forcing (DRF). Results show significant surface SW instantaneous
forcing (up to −90 W m<sup>−2</sup> at noon). Aircraft observations
provide also original estimates of the vertical structure of SW and LW
radiative heating revealing significant instantaneous values of about
5° K per day in the solar spectrum (for a solar angle of
30°) within the dust layer. Associated 3-D modeling studies from
regional climate (RCM) and chemistry transport (CTM) models indicate a
relatively good agreement for simulated AOD compared with observations from
the AERONET/PHOTONS network and satellite data, especially for long-range
dust transport. Calculations of the 3-D SW (clear-sky) surface DRF indicate
an average of about −10 to −20 W m<sup>−2</sup> (for the whole period)
over the Mediterranean Sea together with maxima (−50 W m<sup>−2</sup>)
over northern Africa. The top of the atmosphere (TOA) DRF is shown to be
highly variable within the domain, due to moderate absorbing properties of
dust and changes in the surface albedo. Indeed, 3-D simulations indicate
negative forcing over the Mediterranean Sea and Europe and positive forcing
over northern Africa. Finally, a multi-year simulation, performed for the
2003 to 2009 period and including an ocean–atmosphere (O–A) coupling,
underlines the impact of the aerosol direct radiative forcing on the sea
surface temperature, O–A fluxes and the hydrological cycle over the
Mediterranean. |
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| ISSN: | 1680-7316 1680-7324 |