T. Di Iorio

Saharan dust profiles measured by lidar at Lampedusa

Lidar observations of the tropospheric aerosols were carried out at the island of Lampedusa (35.5°N, 12.6°E) in the Mediterranean during May-June 1999, within the Photochemical Activity and Ultraviolet Radiation II experiment. The measurements indicate that the troposphere is often loaded with large amounts of aerosol particles, producing relatively large values of the depolarization ratio. The aerosol content below and above 2 km shows a somewhat different behavior. In the upper region, large aerosol concentrations last for a few days; during these events aerosol is often detected up to 7 or 8 km. 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 30°N. Large aerosol loads are observed even when the air mass trajectories marginally overpass Africa, often up to 5–6 km. According to the isentropic trajectories, large vertical motions occur when the air masses travel over Africa. Significant differences in the aerosol profiles are found, depending on the origin of the air masses, and on the strength of the vertical motion. All the air masses that have traveled over Africa show an enhanced aerosol concentration, indicating that in this period the conditions were always favorable to dust mobilization and vertical propagation. The identified transport patterns appear to mainly affect the southern Mediterranean; in rare cases, forward trajectories reached southern Italy, Greece, Turkey, and the eastern Mediterranean.

Altitude‐resolved shortwave and longwave radiative effects of desert dust in the Mediterranean during the GAMARF campaign: Indications of a net daily cooling in the dust layer

Desert dust interacts with shortwave (SW) and longwave (LW) radiation, influencing the Earth radiation budget and the atmospheric vertical structure. Uncertainties on the dust role are large in the LW spectral range, where few measurements are available and the dust optical properties are not well constrained. The first airborne measurements of LW irradiance vertical profiles over the Mediterranean were carried out during the Ground-based and Airborne Measurements of Aerosol Radiative Forcing (GAMARF) campaign, which took place in spring 2008 at the island of Lampedusa. The experiment was aimed at estimating the vertical profiles of the SW and LW aerosol direct radiative forcing (ADRF) and heating rates (AHR), taking advantage of vertically resolved measurements of irradiances, meteorological parameters, and aerosol microphysical and optical properties. Two cases, characterized respectively by the presence of a homogeneous dust layer (3 May, with aerosol optical depth, AOD, at 500 nm of 0.59) and by a low aerosol burden (5 May, with AOD of 0.14), are discussed. A radiative transfer model was initialized with the measured vertical profiles and with different aerosol properties, derived from measurements or from the literature. The simulation of the irradiance vertical profiles, in particular, provides the opportunity to constrain model-derived estimates of the AHR. The measured SW and LW irradiances were reproduced when the model was initialized with the measured aerosol size distributions and refractive indices. For the dust case, the instantaneous (solar zenith angle, SZA, of 55.1°) LW-to-SW ADRF ratio was 23% at the surface and 11% at the top of the atmosphere (TOA), with a more significant LW contribution on a daily basis (52% at the surface and 26% at TOA), indicating a relevant reduction of the SW radiative effects. The AHR profiles followed the aerosol extinction profile, with comparable peaks in the SW (0.72 ± 0.11 K d−1) and in the LW (−0.52 ± 0.12 K d−1) for the considered SZA. On a daily basis, the absolute value of the heating rate was larger in the LW than in the SW, producing a net cooling effect at specific levels. These are quite unexpected results, emphasizing the important role of LW radiation.

Desert Aerosol in the Mediterranean

Tropospheric aerosols may affect climate through different mechanisms. In particular, aerosols intervene in the water cycle, and may influence the hydrologic balance. In the Mediterranean a large role is played by desert dust originating in the Sahara. Mineral dust production depends on soil aridity, i.e., among other factors, on land use, and precipitation/temperature regimes. In the Mediterranean, desert dust is mostly transported northward during spring and summer, driven by low and high pressure systems over north Africa. In addition, depending on the synoptic situation, anthropogenic particles and marine aerosols are found over the Mediterranean. The Mediterranean basin is thus an excellent laboratory to study the complex interactions of different type of particles with the radiative field, the hydrological cycle, and clouds. Some results of measurements carried out at Lampedusa island (35.5°N, 12.6°E) in 1999, showing the presence of desert dust and its effects on the radiative field, are described.

Design, development, and testing of an environmental P-T cell for infrared spectroscopy measurements

Water absorption bands due to superficially adsorbed molecules often dominate the near-infrared spectra of particulate minerals and rocks, when measured in the laboratory in the reflectance mode. In order to remove this, the spectral effect is thus necessary to acquire spectra of samples in vacuum and at higher temperatures. With the aim to accomplish this task, we developed an environmental cell to perform infrared spectroscopic measurements at controlled pressure-temperature conditions. Currently the cell allows one to measure reflectance spectra in the temperature range from room values up to 300 °C (573 K), in the pressure range of 103-10-6 mbar. The acquisition of spectra continuously in two distinct phases, namely, during a preliminary pumping stage (at room T) and subsequently during a heating stage (in vacuum), permits to highlight and characterize separately the effect of pressure and temperature on infrared spectra.

The SPectral Imaging (SPIM) facility in support of hyperspectral observations of solar system bodies: Preliminary characterization

The SPectral IMaging (SPIM) facility is a laboratory imaging VIS-IR spectrometer, operative in the INAF/IAPS laboratory in Rome. The facility is used as a laboratory support for the DAWN mission (to the asteroids Vesta and Ceres) and for the 2018 ExoMars mission (to Mars). This imaging spectrometer, which is the spare of the VIR spectrometer [1,2] on-board the DAWN spacecraft, is operative in the 0.22–5.05 μm spectral range. It is characterized by high spatial (38 μm) and spectral (2 nm in the VIS channel, 12 nm in the IR channel) resolution. The high spectral performances, combined with the high spatial resolution imaging capability of this instrument allow a very accurate laboratory investigation and characterization of numerous types of mineral and rock samples, both in powder and in slab form, and also of extra-terrestrial samples, down to a few tens of micrometers in size.

The SPectral IMaging (SPIM) facility in support of hyperspectral observations of solar system bodies

The SPectral IMaging (SPIM) facility is a laboratory imaging VIS-IR spectrometer, operative in the INAF/IAPS laboratory in Rome. The facility is used as a laboratory support for the DAWN mission (to the asteroids Vesta and Cerere) and for the 2018 ExoMars mission (to Mars). This imaging spectrometer, which is the spare of the VIR spectrometer [1] on-board the DAWN spacecraft, is operative in the 0.22–5.1 spectral range. It is characterized by high spatial (38 μm) and spectral (2 nm in the VIS channel, 12 nm in the IR channel) resolution. The high spectral performances, combined with the high spatial resolution imaging capability of this instrument allow a very accurate laboratory investigation and characterization of numerous types of mineral and rock samples, both in powder and in slab form, and also of extraterrestrial samples down to a few tens of micrometers in size (such as for example Interplanetary Dust Particles).