ALBERT

Description: As part of the ChArMEx-ADRIMED campaign (summer 2013), ground-based in situ observations were conducted at the Ersa site (northern tip of Corsica; 533 m a.s.l.) to characterise the optical, physical and chemical properties of aerosols. During the observation period, a major influence of primary marine aerosols was detected (22–26 June), with a mass concentration reaching up to 6.5 µg m−3 and representing more than 40 % of the total PM10 mass concentration. Its relatively low ratio of chloride to sodium (average of 0.57) indicates a fairly aged sea salt aerosol at Ersa. In this work, an original data set, obtained from online real-time instruments (ATOFMS, PILS-IC) has been used to characterise the ageing of primary marine aerosols (PMAs). During this PMA period, the mixing of fresh and aged PMAs was found to originate from both local and regional (Gulf of Lion) emissions, according to local wind measurements and FLEXPART back trajectories. Two different aerosol regimes have been identified: a dust outbreak (dust) originating from Algeria/Tunisia, and a pollution period with aerosols originating from eastern Europe, which includes anthropogenic and biomass burning sources (BBP). The optical, physical and chemical properties of the observed aerosols, as well as their local shortwave (SW) direct radiative effect (DRE) in clear-sky conditions, are compared for these three periods in order to assess the importance of the direct radiative impact of PMAs compared to other sources above the western Mediterranean Basin. As expected, AERONET retrievals indicate a relatively low local SW DRF during the PMA period with mean values of −11 ± 4 at the surface and −8 ± 3 W m−2 at the top of the atmosphere (TOA). In comparison, our results indicate that the dust outbreak observed at our site during the campaign, although of moderate intensity (AOD of 0.3–0.4 at 440 nm and column-integrated SSA of 0.90–0.95), induced a local instantaneous SW DRF that is nearly 3 times the effect calculated during the PMA period, with maximum values up to −40 W m−2 at the surface. A similar range of values were found for the BBP period to those during the dust period (SW DRF at the surface and TOA of −23 ± 6 and −15 ± 4 W m−2 respectively). The multiple sources of measurements at Ersa allowed the detection of a PMA-dominant period and their characterisation in terms of ageing, origin, transport, optical and physical properties and direct climatic impact.

Description: As part of the ChArMEx-ADRIMED campaign (summer 2013), ground-based in-situ observations were conducted at the Ersa site (northern tip of Corsica; 533 m asl) to characterize the physical, optical and chemical properties of aerosols. During the observation period, three different aerosol regimes have been identified, including a dust outbreak (Dust) originating from Algeria/Tunisia, a primary marine aerosols (PMA) event from both the Gulf of Lion and emissions near the sample site, and a pollution period from Eastern Europe, which includes anthropogenic and biomass burning sources (BBP). The chemical, physical and optical properties of the observed aerosols as well as their local shortwave (SW) direct radiative forcing (DRF) in clear-sky conditions are compared for these three periods in order to assess the direct radiative impact of PMA above the Western Mediterranean Basin. The PMA period is characterized by a mean sea salt mass concentration up to 6.5 μg m−3, representing 40 % of the total PM10 mass concentration, and a relatively low ratio of chloride to sodium (average of 0.57) indicating a generally "aged" sea salt aerosol at Ersa. In this work, an original dataset, obtained from on-line real-time instruments (ATOFMS, PILS-IC) have been used to characterize the ageing of PMA. The majority of PMA had surprisingly undergone chemical reactions and were mostly advected from long-range transport. During PMA period, the mixing between fresh and aged PMA originated from both local and regional (Gulf of Lion) emissions. The aerosol optical properties, obtained for the whole atmospheric column and at the surface, indicate a single scattering albedo (SSA) near unity (at 440 nm), indicating almost purely scattering particles, associated to a relatively low aerosol optical depth (AOD) close to 0.1 (at 500 nm), and an aerosol angstrom extinction exponent (AE) equal to 1.3 ± 0.4 (between 440 and 870 nm), suggesting a possible mixing of the PMA with fine particles (probably of continental origin). AERONET retrievals indicate a relatively low local SW DRF during the PMA period with mean values of −11 ± 4 W m−2 at the surface and −8 ± 3 W m−2 at the top of the atmosphere (TOA). In comparison, our results indicate that the dust outbreak observed at our site during the campaign, although of moderate intensity (AOD of 0.3–0.4 at 440 nm and column-integrated SSA of 0.90–0.95), induced a local instantaneous SW DRF nearly three times the forcing calculated during the PMA period, with maximum values up to −40 W m−2 at the surface. On average, the SW DRF was about −21 ± 11 and −14 ± 6 W m−2, at the surface and at TOA, respectively, during this dust outbreak. Finally, the BBP period was characterized by a significant increase of the aerosol PM1 mass concentration (from 3.7 μg m−3 to 7.2 μg m−3) due to the influence of biomass-burning and anthropogenic aerosols transported from Eastern Europe. The influence of polluted/smoke particles led to a significant decrease in SSA (0.90 at 440 nm), showing the important absorbing characteristics of such particles. For this period, the SW DRF at the surface and TOA also exhibit higher mean values compared to the PMA period (with values of −23 ± 6 W m−2 and −15 ± 4 W m−2, respectively) and similar range of values as the Dust period.

Description: The international research program “ReNovRisk-CYCLONE” (RNR-CYC, 2017–2021) directly involves 20 partners from 5 countries of the south-west Indian-Ocean. It aims at improving the observation and modelling of tropical cyclones in the south-west Indian Ocean, as well as to foster regional cooperation and improve public policies adapted to present and future tropical cyclones risk in this cyclonic basin. This paper describes the structure and main objectives of this ambitious research project, with emphasis on its observing components, which allowed integrating numbers of innovative atmospheric and oceanic observations (sea-turtle borne and seismic data, unmanned airborne system, ocean gliders), as well as combining standard and original methods (radiosoundings and global navigation satellite system (GNSS) atmospheric soundings, seismic and in-situ swell sampling, drone and satellite imaging) to support research on tropical cyclones from the local to the basin-scale.