Lidar observations of mesospheric sodium over Italy

We have developed a lidar system for the measurements of the mesospheric atomic sodium (Na) number density profile. The performances and the main characteristics of the system are evaluated showing the first observations: Na number density profiles can be obtained with a resolution of 300 m in altitude and of 200 s in time, the relative uncertainty is between 5% and 10%. These features also allow to discuss the capability of the system to detect the time and space variability of Na density profiles, which is typical of the gravity wave propagation. The preliminary analysis of the sodium profile dynamics along a 7 hours measurement session, started from 19:30UT on 10 April 1997, shows the presence of wave-like perturbations with characteristics typical of propagating gravity waves

Detection of GRB signals with Fluorescence Detectors

Gamma Ray Bursts are being searched in many ground based experiments detecting the high energy component (GeV $\div$ TeV energy range) of the photon bursts. In this paper, Fluorescence Detectors are considered as possible candidate devices for these searches. It is shown that the GRB photons induce fluorescence emission of UV photons on a wide range of their spectrum. The induced fluorescence flux is dominated by GRB photons from 0.1 to about 100 MeV and, once the extinction through the atmosphere is taken into account, it is distributed over a wide angular region. This flux can be detected through a monitor of the diffuse photon flux, provided that its maximum value exceeds a threshold value, that is primarily determined by the sky brightness above the detector. The feasibility of this search and the expected rates are discussed on the basis of the current GRB observations and the existing fluorescence detectors.Comment: 16 pages 9 eps figure

Effective resolution concepts for lidar observations

Abstract. Since its establishment in 2000, EARLINET (European Aerosol Research Lidar NETwork) has provided, through its database, quantitative aerosol properties, such as aerosol backscatter and aerosol extinction coefficients, the latter only for stations able to retrieve it independently (from Raman or high-spectral-resolution lidars). These coefficients are stored in terms of vertical profiles, and the EARLINET database also includes the details of the range resolution of the vertical profiles. In fact, the algorithms used in the lidar data analysis often alter the spectral content of the data, mainly acting as low-pass filters to reduce the high-frequency noise. Data filtering is described by the digital signal processing (DSP) theory as a convolution sum: each filtered signal output at a given range is the result of a linear combination of several signal input data samples (relative to different ranges from the lidar receiver), and this could be seen as a loss of range resolution of the output signal. Low-pass filtering always introduces distortions in the lidar profile shape. Thus, both the removal of high frequency, i.e., the removal of details up to a certain spatial extension, and the spatial distortion produce a reduction of the range resolution. This paper discusses the determination of the effective resolution (ERes) of the vertical profiles of aerosol properties retrieved from lidar data. Large attention has been dedicated to providing an assessment of the impact of low-pass filtering on the effective range resolution in the retrieval procedure

Non-equilibrium evolution of stratospheric particles under multi-components diffusive condensation/evaporation regime

A box model is used to study the evolution of stratospheric HNO3/H2SO4/H2O solution particles along temperature variations, which force the droplet ensemble far from the thermodynamic equilibrium. In the case of rapid temperature fluctuations, i.e. orographically forced lee waves, the model shows that the micron-sized droplets meet the conditions to become precursors of solid particles, mainly constituted of nitric acid hydrates. This paper examines how the particle size distributions and compositions are influenced by the presence of rapid temperature fluctuations, comparing model calculations along prescribed thermal histories. There results a remarkable dependence of the particle physical status (solid and/or liquid) on the presence of wave-like perturbations in the former thermal history of the air mass

Sensible heat flux and boundary layer depth measurements by Doppler SODAR and sonic anemometer data

A validation of a simple mixed-layer similarity relationship, firstly proposed by Panofsky and McCormick (1960), is presented for wind speeds up to 7 ms21 and over an uneven terrain. The surface heat flux and the Planetary Boundary Layer depth, zi, are retrieved from this relationship, by using SODAR measurements of the vertical velocity variance s 2 w, under the hypothesis that the heat flux linearly decreases with height. All the measurements are relative to days characterized by high-pressure conditions, during periods of well-developed convection. The values of the surface heat flux obtained from such a method are compared with those obtained by applying the eddy correlation technique to the vertical wind velocities and virtual temperatures measured by a sonic anemometer. The values of zi obtained from the same relationship are compared with the height of the lowest inversion layer estimated from the facsimile record of the echoes received by the vertical antenna of the SODAR. The spectral behavior of vertical and longitudinal wind velocity from the anemometer and the SODAR is examined, too. In such a way an independent estimate of zi is obtained from the position of the spectral maximum

A combined Rayleigh-Raman lidar for measurements of tropospheric water vapour and aerosol profiles

The receiver of the Differential Absorption Lidar system of the University of L’Aquila (Italy) has been upgraded for the detection of Raman scattering from nitrogen and water vapour induced by XeCl and XeF excimer laser lines. In this configuration, only the XeF source is activated, so we can measure the tropospheric water vapour mixing ratio profiles with a height resolution of 300 m and 10 min in time. The lower limit sensitivity for the mixing ratio of water vapour is about 2 Q1024 and the precision ranges between 5% at 2 km and 50% at 9 km. The aerosol back-scattering ratio profiles can be measured with the same altitude and time resolution up to the lower stratosphere, the relative error is below 5% in the troposphere and about 30% at the highest altitudes. Comparisons with coincident PTU balloon-sondes show that the performances of the system in measuring the tropospheric water vapour are well calibrated for studying the water vapour evolution and cloud formation in the troposphere

Overview: Tropospheric profiling: state of the art and future challenges – introduction to the AMT special issue

Abstract. This paper introduces the Atmospheric Measurement Techniques special issue on tropospheric profiling, which was conceived to host full papers presenting the results shown at the 9th International Symposium on Tropospheric Profiling (ISTP9). ISTP9 was held in L'Aquila (Italy) from 3 to 7 September 2012, bringing together 150 scientists representing of 28 countries and 3 continents. The tropospheric profiling special issue collects the highlights of ISTP9, reporting recent advances and future challenges in research and technology development

Description of Atmospheric Conditions at the Pierre Auger Observatory Using Meteorological Measurements and Models

Atmospheric conditions at the site of a cosmic ray observatory must be known well for reconstructing observed extensive air showers, especially when measured using the fluorescence technique. For the Pierre Auger Observatory, a sophisticated network of atmospheric monitoring devices has been conceived. Part of this monitoring was a weather balloon program to measure atmospheric state variables above the Observatory. To use the data in reconstructions of air showers, monthly models have been constructed. Scheduled balloon launches were abandoned and replaced with launches triggered by high-energetic air showers as part of a rapid monitoring system. Currently, the balloon launch program is halted and atmospheric data from numerical weather prediction models are used. A description of the balloon measurements, the monthly models as well as the data from the numerical weather prediction are presented

Ozone, aerosols and polar stratospheric clouds measurements during the EASOE Campaign

Preliminary results are presented of observations obtained during the EASOE campaign, with an airborne backscatter lidar and a ground-based DIAL ozone lidar system. Although the main signature observed on the lidar signals was due to the Pinatubo cloud which erupted in June 1991, distinct PSC events were detected on several occasions by the airborne lidar often in relation with orographic wave activity over the norvegian mountains. The ozone profiles obtained in Sodankyla with the ground based lidar are locally perturbed by the presence of the volcanic cloud. After a first correction of the aerosols effect, they present however a reasonably good agreement with the ozone sondes profiles performed on the same site

Infrared ellipsometry study of the confined electrons in a high-mobility <i>γ</i>-Al₂O₃/SrTiO₃ heterostructure

With infrared ellipsometry we studied the response of the confined electrons in γ-Al₂O₃/SrTiO₃ (GAO/STO) heterostructures in which they originate predominantly from oxygen vacancies. From the analysis of a so-called Berreman mode, that develops near the highest longitudinal optical phonon mode of SrTiO₃, we derive the sheet carrier density, N s , the mobility, μ, and the depth profile of the carrier concentration. Notably, we find that N s and the shape of the depth profile are similar as in LaAlO₃/SrTiO₃ (LAO/STO) heterostructures for which the itinerant carriers are believed to arise from a polar discontinuity. Despite an order of magnitude higher mobility in GAO/STO, as obtained from transport measurements, the derived mobility in the infrared range exhibits only a twofold increase. We interpret this finding in terms of the polaronic nature of the confined charge carriers in GAO/STO and LAO/STO which leads to a strong, frequency-dependent interaction with the STO phonons