Synoptic conditions favouring the occurrence of aerosol episodes over the broader Mediterranean basin

Gkikas, Antonis; Houssos, E. E.; Hatzianastassiou, N.; Papadimas, C. D.; Bartzokas, A.

doi:10.1002/qj.978

Cited by 60 publications

(60 citation statements)

References 82 publications

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“…It is worth mentioning that available data are provided by stations that are located for most of them in the western Mediterranean. However, in summer most of the dust outbreaks occur in this region because of frequent low-pressure systems over Morocco that favour the dust export over the western Mediterranean (Moulin et al, 1998;Gkikas et al, 2012).…”

Section: Observation Datamentioning

confidence: 99%

“…Indeed, dust particles coming from suspension, saltation and creeping processes associated with wind erosion (Knippertz and Todd, 2012) can move from northern Africa to the Mediterranean Sea and Europe (Moulin et al, 1997;Papadimas et al, 2008;Gkikas et al, 2013). These dust outbreaks are mainly driven by the synoptic meteorological conditions (Gkikas et al, 2012): they are more frequent in the eastern basin in winter and spring, in the central basin in spring and in the western basin in summer (Moulin et al, 1998). The ChArMEx initiative (Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr) has been launched for a few years in the framework of the MIS-TRALS (Mediterranean Integrated STudies at Regional And Local Scales) programme in order to improve our knowledge of aerosols and their impacts on climate in the Mediterranean.…”

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confidence: 99%

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Dust aerosol radiative effects during summer 2012 simulated with a coupled regional aerosol–atmosphere–ocean model over the Mediterranean

et al. 2015

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Abstract. The present study investigates the radiative effects of dust aerosols in the Mediterranean region during summer 2012 using a coupled regional aerosol-atmosphere-ocean model (CNRM-RCSM5). A prognostic aerosol scheme, including desert dust, sea salt, organic, black-carbon and sulphate particles, has been integrated to CNRM-RCSM5 in addition to the atmosphere, land surface and ocean components. An evaluation of this aerosol scheme of CNRM-RCSM5, and especially of the dust aerosols, has been performed against in situ and satellite measurements, showing its ability to reproduce the spatial and temporal variability of aerosol optical depth (AOD) over the Mediterranean region in summer 2012. The dust vertical and size distributions have also been evaluated against observations from the TRAQA/ChArMEx campaign. Three simulations have been carried out for summer 2012 with CNRM-RCSM5, including the full prognostic aerosol scheme, only monthly-averaged AOD means from the aerosol scheme or no aerosols at all, in order to focus on the radiative effects of dust particles and the role of the prognostic scheme. Surface short-wave aerosol radiative forcing variability is found to be more than twice as high over regions affected by dust aerosols, when using a prognostic aerosol scheme instead of monthly AOD means. In this case downward surface solar radiation is also found to be better reproduced according to a comparison with several stations across the Mediterranean. A composite study over 14 stations across the Mediterranean, designed to identify days with high dust AOD, also reveals the improvement of the representation of surface temperature brought by the use of the prognostic aerosol scheme. Indeed the surface receives less radiation during dusty days, but only the simulation using the prognostic aerosol scheme is found to reproduce the observed intensity of the dimming and warming on dusty days. Moreover, the radiation and temperature averages over summer 2012 are also modified by the use of prognostic aerosols, mainly because of the differences brought in short-wave aerosol radiative forcing variability. Therefore this first comparison over summer 2012 highlights the importance of the choice of the representation of aerosols in climate models.

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Section: Observation Datamentioning

confidence: 99%

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confidence: 99%

Dust aerosol radiative effects during summer 2012 simulated with a coupled regional aerosol–atmosphere–ocean model over the Mediterranean

et al. 2015

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“…Dust aerosols are indeed transported over the Mediterranean Sea during successing outbreaks, occuring first in spring in the eastern basin, and then moving westwards in summer. These outbreaks are due to intense dust uplift over the Libyan and Egyptian deserts in spring (Moulin et al 1998) and favourable circulation patterns (Gkikas et al 2012). In summer, frequent low pressure systems over northern Morocco favour the dust export over the western basin (Moulin et al 1998).…”

Section: Aerosol Variabilitymentioning

confidence: 99%

Direct and semi-direct aerosol radiative effect on the Mediterranean climate variability using a coupled regional climate system model

et al. 2014

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A fully coupled regional climate system model (CNRM-RCSM4) has been used over the Mediterranean region to investigate the direct and semi-direct effects of aerosols, but also their role in the radiation-atmosphereocean interactions through multi-annual ensemble simulations (2003)(2004)(2005)(2006)(2007)(2008)(2009)) with and without aerosols and oceanatmosphere coupling. Aerosols have been taken into account in CNRM-RCSM4 through realistic interannual monthly AOD climatologies. An evaluation of the model has been achieved, against various observations for meteorological parameters, and has shown the ability of CNRM-RCSM4 to reproduce the main patterns of the Mediterranean climate despite some biases in sea surface temperature (SST), radiation and cloud cover. The results concerning the aerosol radiative effects show a negative surface forcing on average because of the absorption and scattering of the incident radiation. The SW surface direct effect is on average -20.9 Wm -2 over the Mediterranean Sea, -14.7 Wm -2 over Europe and -19.7 Wm -2 over northern Africa. The LW surface direct effect is weaker as only dust aerosols contribute (?4.8 Wm -2 over northern Africa). This direct effect is partly counterbalanced by a positive semi-direct radiative effect over the Mediterranean Sea (?5.7 Wm -2 on average) and Europe (?5.0 Wm -2 ) due to changes in cloud cover and atmospheric circulation. The total aerosol effect is consequently negative at the surface and responsible for a decrease in land (on average -0.4°C over Europe, and -0.5°C over northern Africa) and sea surface temperature (on average -0.5°C for the Mediterranean SST). In addition, the latent heat loss is shown to be weaker (-11.0 Wm -2 ) in the presence of aerosols, resulting in a decrease in specific humidity in the lower troposphere, and a reduction in cloud cover and precipitation. Simulations also indicate that dust aerosols warm the troposphere by absorbing solar radiation, and prevent radiation from reaching the surface, thus stabilizing the troposphere. The comparison with the model response in atmosphere-only simulations shows that these feedbacks are attenuated if SST cannot be modified by aerosols, highlighting the importance of using coupled regional models over the Mediterranean. Oceanic convection is also strengthened by aerosols, which tends to reinforce the Mediterranean thermohaline circulation. In parallel, two case studies are presented to illustrate positive feedbacks between dust aerosols and regional climate. First, the eastern Mediterranean was subject to high dust aerosol loads in June 2007 which reduce land and sea surface temperature, as well as air-sea humidity fluxes. Because of northern wind over the eastern Mediterranean, drier and cooler air has been consequently advected from the sea to the African continent, reinforcing the direct dust effect over land. On the contrary, during the western European heat wave in June 2006, dust aerosols have contributed to reinforcing an important ridge responsible for dry and 123Cl...

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“…The Mediterranean region is a complex area where atmospheric aerosols of different origins and types may be found (Pace et al, 2006;Kallos et al, 2007;Gkikas et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Continental pollution in the western Mediterranean basin: vertical profiles of aerosol and trace gases measured over the sea during TRAQA 2012 and SAFMED 2013

et al. 2015

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Abstract. In this study we present airborne observations of aerosol and trace gases obtained over the sea in the western Mediterranean basin during the TRAQA (TRansport and Air QuAlity) and SAFMED (Secondary Aerosol Formation in the MEDiterranean) campaigns in summer 2012 and 2013. A total of 23 vertical profiles were measured up to 5000 m above sea level over an extended area (40-45 • N and 2 • W-12 • E) including the Gulf of Genoa, southern France, the Gulf of Lion, and the Spanish coast. During TRAQA and SAFMED the study area experienced a wide range of meteorological conditions which favoured pollution export from different sources located around the basin. Also, several events of dust outflows were measured during the campaigns. Observations from the present study show that continental pollution largely affects the western Mediterranean both close to coastal regions and in the open sea as far as ∼ 250 km from the coastline. The measured aerosol scattering coefficient varies between ∼ 20 and 120 Mm −1 , while carbon monoxide (CO) and ozone (O 3 ) mixing ratios are in the range of 60-165 and 30-85 ppbv, respectively. Pollution reaches 3000-4000 m in altitude and presents a very complex and highly stratified structure characterized by fresh and aged layers both in the boundary layer and in the free troposphere. Within pollution plumes the measured particle concentration in the Aitken (0.004-0.1 µm) and accumulation (0.1-1.0 µm) modes is between ∼ 30 and 5000-6000 scm −3 (standard cm −3 ), which is comparable to the aerosol concentration measured in continental areas under pollution conditions. Additionally, our measurements indicate the presence of highly concentrated Aitken layers (10 000-15 000 scm −3 ) observed both close to the surface and in the free troposphere, possibly linked to the influence of new particle formation (NPF) episodes over the basin.

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Synoptic conditions favouring the occurrence of aerosol episodes over the broader Mediterranean basin

Cited by 60 publications

References 82 publications

Dust aerosol radiative effects during summer 2012 simulated with a coupled regional aerosol–atmosphere–ocean model over the Mediterranean

Dust aerosol radiative effects during summer 2012 simulated with a coupled regional aerosol–atmosphere–ocean model over the Mediterranean

Direct and semi-direct aerosol radiative effect on the Mediterranean climate variability using a coupled regional climate system model

Continental pollution in the western Mediterranean basin: vertical profiles of aerosol and trace gases measured over the sea during TRAQA 2012 and SAFMED 2013

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