In the upper region, large aerosol concentrations last for a few days; during these events aerosol is often detected up to 7 or 8 kin. Large amounts were detected in mid-May and were very often observed in June. By using meteorological analyses and isentropic backward trajectories, the aerosol behavior above Lampedusa has been related to the large-scale transport patterns and to the source regions. Large aerosol loads are clearly due to dust transport from Africa, occurring through two main paths: from central Sahara, when a high-pressure system was centered over northern Libya, and following the northwestern African coast, often along the Atlas Mountains, when the anticyclone is over Algeria or Libya, at latitudes lower than 30øN. Large aerosol loads are observed even when the air mass trajectories marginally overpass Africa, often up to 5-6 kin. According to the isentropic trajectories, large vertical motions occur when the air masses travel over Africa. Significant differences in the aerosol

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[1] Measurements of the aerosol properties were carried out at the island of Lampedusa, in the Mediterranean, in May 1999, as part of the Photochemical Activity and Ultraviolet Radiation modulating factors II campaign. Data from ground-based lidar and Sun photometer, and particle counters aboard an instrumented ultralight aircraft, are used in this study. Three different cases, when all the measurements were available in cloud-free conditions, were identified to derive the aerosol microphysical and optical properties. In one of these cases (18 May) the airmasses originated from Africa, and were loaded with a large amount of desert dust. In the other two cases (25 May and 27 May) the airmasses passed over Europe before reaching Lampedusa from North. The microphysical and optical properties of the aerosol strongly depend on the origin of the airmasses. The amount of particles in the 1-6 mm range of radii and the average aerosol surface area per unit volume are larger in the desert dust case than on 25 May and 27 May. The real part of the refractive index of the desert dust at 532 nm is between 1.52 and 1.58; its imaginary part is 5-7 Â 10 À3 and the single scattering albedo is about 0.7-0.75. The aerosol layer of 18 May closest to the surface, that probably contains a mixture of desert dust and marine aerosol, displays a smaller imaginary part (1.2 Â 10 À3 ) and a larger single scattering albedo (0.91). The aerosols originating from the North Atlantic and Europe have a real part of the refractive index between 1.35 and 1.49, and an imaginary part ranging from 8 Â 10 À4 to 1.8 Â 10 À2 ; the single scattering albedo at 532 nm (0.78-0.95) is larger than for desert dust values. The smallest value of the single scattering albedo (0.69) corresponds to an airmass originating from North, characterized by a large imaginary part of the refractive index. The asymmetry factor of the desert dust appears consistently larger for the desert dust (0.75-0.8) than for the other cases (0.61-0.72). The extinction-to-backscattering ratio, also derived from the measurements, is about 40 sr for the desert dust, and between 60 and 81 sr for the aerosol of northern origin. Simple estimates of the aerosol average direct shortwave radiative forcing at the top of the atmosphere indicate that all considered aerosol types induce a cooling. The radiative forcing per unit optical depth of the aerosol originating from North is about À37 Wm À2 over ocean and À(12-17) Wm À2 over land, while is À29 Wm À2 over ocean and À8 Wm À2 over land for desert dust. The largest forcing is however produced by the desert aerosols that generally display a considerably larger optical depth.

[1] The seasonal evolution of the aerosol vertical distribution in the Central Mediterranean is studied using measurements made in the period 1999-2008 at Lampedusa with an aerosol Lidar and a multi filter rotating shadowband radiometer (MFRSR). Measurements show that the aerosol vertical distribution is largely influenced by Saharan dust, which produces a strong annual cycle both in aerosol vertical extension and optical depth. Dust layers are present in the profile in 38% of the cases throughout the year, and in 57% in summer. The dust top altitude peaks in late spring, up to 9 km. The monthly average optical depth at 500 nm for dust cases shows a main peak in July (0.38), and values exceeding 0.2 throughout March-September. Conversely, non-dust cases show a very limited seasonality, both in vertical distribution and aerosol optical depth. The monthly average optical depth for non-dust cases is smaller than 0.17 throughout the year. During winter, the vertical distribution and optical depth are very similar for both dust and non-dust cases. The seasonal average extinction coefficient profiles for dust and non-dust cases show remarkable differences in spring and summer, when values of the extinction coefficient exceed 0.5 Â 10 À4 m À1 throughout the altitude range 0-4.5 km for dust cases, and 0-1 km altitude for non-dust cases, respectively. Estimates of the Lidar Ratio are derived by combining Lidar and MFRSR measurements. The average Lidar Ratio at 532 nm is about 30 sr.

[1] This paper presents the project Earth Cooling by Water Vapor Radiation, an observational programme, which aims at developing a database of spectrally resolved far infrared observations, in atmospheric dry conditions, in order to validate radiative transfer models and test the quality of water vapor continuum and line parameters. The project provides the very first set of far-infrared spectral downwelling radiance measurements, in dry atmospheric conditions, which are complemented with Raman Lidar-derived temperature and water vapor profiles. Citation: Bhawar, R., et al. (2008), Spectrally resolved observations of atmospheric emitted radiance in the H 2 O rotation band, Geophys. Res. Lett., 35, L04812,

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[1] In February-March 1999, nocturnal observations with a ground-based backscatter/ depolarization lidar were conducted during the Airborne Platform for Earth ObservationThird European Stratospheric Experiment on Ozone (APE-THESEO) campaign at Mahé, Seychelles (4.4°S, 55.3°E). Upper tropospheric cirrus clouds were a common feature in the lidar echoes; they were detected for about 67 hours out of a total measurement time of 125 hours. Optical and geometrical characteristics of the clouds detected at altitudes above 9 km throughout the campaign are derived and discussed. Cirri above 14.5 km present a layered structure and appear more persistent and thinner than cirri at lower altitudes. The behavior of average optical and geometrical depths, integrated depolarization, backscatter-to-extinction ratio, integrated backscatter, and extinction coefficient is studied as a function of midcloud temperature and is compared with results from previous measurements and models. The estimated cloud backscatter-to-extinction ratio ranges from 0.01 to 0.2 sr À1 , with an average value of 0.051 ± 0.030 sr À1 . In the temperature range between 200 and 240 K the integrated depolarization ranges between 0.27 and 0.19 and appears lower than that for midlatitude cirri. In a single night, very high values of the integrated depolarization for a layered cirrus at 16 km could be related to outflow from an active convective cell. The two highest and coldest (temperature around 188 K) layers show values of optical and geometrical depth and integrated depolarization lower than for cirri at temperatures between 190 and 200 K. The optical characteristics of the clouds decrease for temperatures from 190 to 200 K, possibly indicating different evolution phases of the clouds.