Gianluca Pisani

Vertical profiling of Saharan dust with Raman lidars and airborne HSRL in southern Morocco during SAMUM

Three ground-based Raman lidars and an airborne high-spectral-resolution lidar (HSRL) were operated duringSAMUM 2006 in southern Morocco to measure height profiles of the volume extinction coefficient, the extinction-to-backscatter ratio and the depolarization ratio of dust particles in the Saharan dust layer at several wavelengths. Aerosol Robotic Network (AERONET) Sun photometer observations and radiosoundings of meteorological parameters complemented the ground-based activities at the SAMUM station of Ouarzazate. Four case studies are presented. Two case studies deal with the comparison of observations of the three ground-based lidars during a heavy dust outbreak and of the ground-based lidars with the airborne lidar. Two further cases show profile observations during satellite overpasses on 19 May and 4 June 2006. The height resolved statistical analysis reveals that the dust layer top typically reaches 4–6 km height above sea level (a.s.l.), sometimes even 7 km a.s.l.. Usually, a vertically inhomogeneous dust plume with internal dust layers was observed in the morning before the evolution of the boundary layer started. The Saharan dust layer was well mixed in the early evening. The 500 nm dust optical depth ranged from 0.2–0.8 at the field site south of the High Atlas mountains, Ångström exponents derived from photometer and lidar data were between 0–0.4. The volume extinction coefficients (355, 532 nm) varied from 30–300Mm−1 with a mean value of 100Mm−1 in the lowest 4 km a.s.l.. On average, extinction-to-backscatter ratios of 53–55 sr (±7–13 sr) were obtained at 355, 532 and 1064 nm.

EARLINET observations of the 14-22-May long-range dust transport event during SAMUM 2006: validation of results from dust transport modelling

We observed a long-range transport event of mineral dust from North Africa to South Europe during the Saharan Mineral Dust Experiment (SAMUM) 2006. Geometrical and optical properties of that dust plume were determined with Sun photometer of the Aerosol Robotic Network (AERONET) and Raman lidar near the North African source region, and with Sun photometers of AERONET and lidars of the European Aerosol Research Lidar Network (EARLINET) in the far field in Europe. Extinction-to-backscatter ratios of the dust plume over Morocco and Southern Europe do not differ. Ångström exponents increase with distance from Morocco. We simulated the transport, and geometrical and optical properties of the dust plume with a dust transport model. The model results and the experimental data show similar times regarding the appearance of the dust plume over each EARLINET site. Dust optical depth from the model agrees in most cases to particle optical depth measured with the Sun photometers. The vertical distribution of the mineral dust could be satisfactorily reproduced, if we use as benchmark the extinction profiles measured with lidar. In some cases we find differences. We assume that insufficient vertical resolution of the dust plume in the model calculations is one reason for these deviations.

EAQUATE: An International Experiment For Hyperspectral Atmospheric Sounding Validation

The international experiment called the European Aqua Thermodynamic Experiment (EAQUATE) was held in September 2004 in Italy and the United Kingdom to validate Aqua satellite Atmospheric Infrared Sounder (AIRS) radiance measurements and derived products with certain groundbased and airborne systems useful for validating hyperspectral satellite sounding observations. A range of flights over land and marine surfaces were conducted to coincide with overpasses of the AIRS instrument on the Earth Observing System Aqua platform. Direct radiance evaluation of AIRS using National Polar-Orbiting Operational Environmental Satellite System (NPOESS) Airborne Sounder Testbed-Interferometer (NAST-I) and the Scanning High-Resolution Infrared Sounder has shown excellent agreement. Comparisons of level-2 retrievals of temperature and water vapor from AIRS and NAST-I validated against high-quality lidar and dropsonde data show that the 1-K/l-km and 10%/1-km requirements for temperature and water vapor (respectively) are ge...

Volcanic ash concentration during the 12 August 2011 Etna eruption

Mount Etna, in Italy, is one of the most active volcanoes in the world and an ideal laboratory to improve volcano ash monitoring and forecasting. During the volcanic episode on 12 August 2011, an eruption column rose up to several kilometers above sea level (asl), and the volcanic plume dispersed to the southeast. From the video-surveillance system, we were able to estimate variations in the column height (peak value of 9.5 ± 0.5 km above sea level) with time. We derived the time-varying discharge rate (peak value of 60 m3 s−1) and determined the ash concentration using a volcanic ash dispersal model. The modeled ash concentration was compared with lidar measurements using different particle effective radius, and differences are within the error bars. Volcanic ash concentrations range from 0.5 to 35.5 × 10−3 g m−3. The comparison highlights that to improve volcanic ash forecasting during volcanic crises it is necessary to take into account the time-varying discharge rate of explosive eruptions.

Characterization of atmospheric aerosol in the urban area of Napoli in the framework of EARLINET Project

Systematic Lidar measurements of tropospheric aerosols optical properties have been carried out in the urban area of Napoli (Southern Italy, 40°50’18”N, 14°10’59”E, 118 m above sea level), in the framework of EARLINET project. Lidar systematic measurements of aerosol backscattering and extinction profiles have been performed at laser wavelength of 351nm and were obtained from simultaneously measurements of elastic and N2 Raman signals. Following the EARLINET protocol, regular measurements have been performed three times a week in two days and they provide information on aerosol optical properties, with a final spatial resolution of 60m and a temporal resolution between 1 and 30 min. A statistical analysis in terms of integrated backscattering (BI), optical depth (OD), extinction to backscattering ratio (LR), and Dust Layer height (DL), obtained from measurements carried out in clear sky conditions over 30 months, has been realized. Further measurements have been performed during Saharan Dust transport events and some detailed observation of complete diurnal cycle has been carried out, in order to know the dynamic and the evolution of the Planetary Boundary Layer

CALIPSO correlative measurements at Napoli EARLINET station

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite had been launched in April 2006. Its main goal is to probe the vertical structure and to measure the properties of thin clouds and aerosols plume of the Earths atmosphere. In order to validate the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) products, correlative measurements between CALIPSO and EARLINET stations have been planned in the framework of the validation campaign. At Napoli EARLINET station correlative measurement have been performed starting from the beginning of June 2006. Results obtained both during daytime with elastic lidar and nighttime with Raman lidar operating at two wavelengths (355nm and 532nm) are shown. The results of the application of a new algorithm to retrieve aerosol basckscattering and extinction coefficient backscattering from space and ground based elastic lidar signals are presented. Case study of Saharan dust outbreaks and cirrus clouds captured during correlative measurement runs are discussed.

Atmospheric aerosol characterization during Saharan dust outbreaks at Naples EARLINET station

The optical properties and the spatial distribution of the tropospheric aerosols over Naples under Saharan dust outbreaks conditions have been studied by means of lidar measurements performed between May 2000 and August 2003 in the frame of the EARLINET project. Climatological analysis of sand plume has been done by comparing normal and dust affected conditions. Results in terms of backscattering and extinction coefficient as well as their integrated quantities show that the aerosol load from the ground level up to 2 Km during Saharan dust transport events is almost the same of normal conditions. This is probably due to the relevant widespread of local aerosol sources, such as vehicular traffic, industrial activities, etc. Nevertheless, when sand outbreaks occur, the extinction to backscattering ratio, i.e. the lidar ratio, clearly shows that the aerosol type in the lowest atmospheric layer changes. Moreover, Saharan dust transport events strong increase both integrated backscatter and optical dept above 2 km.