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 Forcing on the Mediterranean Climate (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 set-up 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 modelling 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 produce high level of atmospheric pollutants nor intense biomass burning events in the region. However, numerous mineral dust plumes were observed during the campaign with main sources located in Morocco, Algeria and Tunisia, leading to aerosol optical depth (AOD) values ranging between 0.2 to 0.6 (at 440 nm) over the western and central Mediterranean basins. Associated aerosol extinction values measured on-board the ATR-42 within the dust plume show local maxima reaching up to 150 Mm−1. Non negligible aerosol extinction (about 50 Mm−1) was also been observed within the Marine Boundary Layer (MBL). By combining ATR-42 extinction, absorption and scattering measurements, a complete optical closure has been made revealing excellent agreement with estimated optical properties. Associated calculations of the dust single scattering albedo (SSA) have been conducted, which show a moderate variability (from 0.90 to 1.00 at 530 nm). 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-salt 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 show particle size distributions characterized by large aerosols (> 10 μm in diameter) within dust plumes. 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 direct radiative forcing (DRF). Results show significant surface SW instantaneous forcing (up to −90 W m−2 at noon). Associated 3-D modeling studies from regional climate (RCM) and chemistry transport (CTM) models indicate a relatively good agreement for simulated AOD compared with measurements/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−2 (for the whole period) over the Mediterranean Sea together with maxima (−50 W m−2) 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.

Highlights

  • The Mediterranean region has been identified as one of the most prominent “Hot-Spots” in future climate change projections (Giorgi and Lionello, 2008)

  • In the first and second parts (Sects. 2 and 3), we describe the in situ and remote-sensing instrumentation deployed at the two super-sites (Ersa and Lampedusa) and secondary sites (Minorca, Capo Granitola and the Barcelona and Granada EARLINET/ACTRIS stations), the additional AERONET/PHOTONS (AErosol RObotic NETwork/PHOtométrie pour le Traitement Opérationnel de Normalisation Satellitaire, http://aeronet.gsfc.nasa.gov/; Holben et al, 1998) and EARLINET/ACTRIS (European Aerosol Research Lidar Network/Aerosols, Clouds, and Trace gases Research InfraStructure Network, http://www. actris.net/; Pappalardo et al, 2014) network stations that we used, and the airborne observations obtained onboard the two French research aircraft (ATR-42 and F-20) and with sounding and drifting balloons

  • The special observing period (SOP-1a) performed during the Mediterranean dry season (11 June to 5 July 2013) over the western and central Mediterranean basins has been described in detail, as well as the 1-D to 3-D modeling effort, involved in the Chemistry-Aerosol Mediterranean Experiment (ChArMEx)/ADRIMED project focused on aerosol-radiation-climate interactions

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Summary

Introduction

The Mediterranean region has been identified as one of the most prominent “Hot-Spots” in future climate change projections (Giorgi and Lionello, 2008). Aerosols have a significant effect on photolysis rates that may affect tropospheric chemistry and ozone production over the basin (Casasanta et al, 2011; Mailler et al, 2015) With regards to such surfaces, TOA and atmospheric forcings, there is a need to investigate how the change in the radiative budget due to natural/anthropogenic aerosols influences surface temperature (both over land and sea), relative humidity profiles, exchanges (latent heat fluxes) between ocean and atmosphere, cloud cover (semi-direct effect of absorbing particles), precipitation and the whole Mediterranean hydrological cycle. An example of results of longer (inter-seasonal and inter-annual) aerosol-climate simulations is presented in Sect. 6, based on the work of Nabat et al (2015a)

The Cape Corsica and Lampedusa surface super-sites
CARAGA 1 pyranometer 1 pyrgeometer
In situ measurements at super-sites
Remote-sensing and radiation measurements at super-sites
Montesoro station
Granada station
Minorca station
Capo Granitola station
Surface remote-sensing network
Overview of the ATR-42 and F-20 flights
In situ and remote-sensing observations onboard the ATR-42
LNG observations
OSIRIS observations
Balloon operations
Synoptic situation
An aged smoke plume advected over Europe
Aerosol mass and number concentration at the two super-sites
Columnar particle volume size distribution
Particle size distribution during transport
Aerosol chemical composition
In situ optical properties at the surface
Remote-sensing observations from the surface
ATR-42 and F-20 aircraft observations
Lidar surface observations
Sounding balloon observations
Local direct radiative forcing
Estimates using in situ radiative flux observations
Estimations of the SW and LW radiative heating rate along the vertical
Overview of modeling activities
COSMO-MUSCAT model
The CHIMERE chemistry transport model
The RegCM regional climate model
The CNRM-RCSM regional climate model
Aerosol optical depth
Regional SW 3-D direct radiative forcing
13 Jun–5 Jul
Findings
Conclusions
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