In‐cloud variability of LIDAR depolarization of polar and midlatitude cirrus

LIDAR depolarization is commonly used for discriminating liquid and ice particles. Since depolarization depends in a complicated manner on particle shape and size, in‐cloud variability of depolarization has been used as an indicator of the microphysical homogeneity of cirrus. The comparison between midlatitude (Florence, Italy, 43. 60°N) and polar (Dumont d'Urville, Antarctica, 66. 68°S) cirrus showed a lower mean depolarization and a higher in‐cloud uniformity of cloud depolarization for polar clouds in the (−80, −50°C) temperature range. A wider in‐cloud variability of depolarization was observed in polar clouds at higher temperatures (−50, −30°C), reflecting the presence of supercooled liquid layers. The large in‐cloud variability of depolarization in Florence cirrus could be explained with a microphysics that is dynamically and chemically perturbed as compared with the polar site. Aged jet contrails are, in fact, present in many Florence cirrus records

Far-Infrared Radiative Properties of Water Vapor and Clouds in Antarctica

Abstract Water vapor and clouds are among the most important greenhouse components whose radiative features cover all the broad spectral range of the thermal emission of the atmosphere. Typically more than 40% of the total thermal emission of Earth occurs in the far-infrared (FIR) spectral region from 100 to 667 cm−1 (wavelengths from 100 to 15 µm). Nevertheless, this spectral region has not ever been fully covered down to 100 cm−1 by space missions, and only a few ground-based experiments exist because of the difficulty of performing measurements from high altitude and very dry locations where the atmosphere is sufficiently transparent to observe the FIR emission features. To cover this lack of observations, the Italian experiment "Radiative Properties of Water Vapor and Clouds in Antarctica" has collected a 2-yr dataset of spectral measurements of the radiance emitted by the atmosphere and by clouds, such as cirrus and polar stratospheric clouds, from 100 to 1,400 cm−1 (100–7 µm of wavelength), including the underexplored FIR region, along with polarization-sensitive lidar observations, daily radiosondes, and other ancillary information to characterize the atmosphere above the site. Measurements have been performed almost continuously with a duty cycle of 6 out of 9 h, from the Italian–French base of Concordia at Dome C over the Antarctic Plateau at 3,230 m MSL, in all-sky conditions since 2012. Because of the uniqueness of the observations, this dataset will be extremely valuable for evaluating the accuracy of atmospheric absorption models (both gas and clouds) in the underexplored FIR and to detect possible daily, seasonal, and annual climate signatures

Genesis of diamond dust, ice fog and thick cloud episodes observed and modelled above Dome C, Antarctica

Abstract. Episodes of thick cloud and diamond dust/ice fog were observed during 15 March to 8 April 2011 and 4 to 5 March 2013 in the atmosphere above Dome C (Concordia station, Antarctica; 75°06′ S, 123°21′ E; 3233 m a.m.s.l.). The objectives of the paper are mainly to investigate the processes that cause these episodes based on observations and to verify whether operational models can evaluate them. The measurements were obtained from the following instruments: (1) a ground-based microwave radiometer (HAMSTRAD, H2O Antarctica Microwave Stratospheric and Tropospheric Radiometers) installed at Dome C that provided vertical profiles of tropospheric temperature and absolute humidity every 7 min; (2) daily radiosoundings launched at 12:00 UTC at Dome C; (3) a tropospheric aerosol lidar that provides aerosol depolarization ratio along the vertical at Dome C; (4) down- and upward short- and long-wave radiations as provided by the Baseline Surface Radiation Network (BSRN) facilities; (5) an ICE-CAMERA to detect at an hourly rate the size of the ice crystal grains deposited at the surface of the camera; and (6) space-borne aerosol depolarization ratio from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) lidar aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) platform along orbits close to the Dome C station. The time evolution of the atmosphere has also been evaluated by considering the outputs from the mesoscale AROME and the global-scale ARPEGE meteorological models. Thick clouds are detected during the warm and wet periods (24–26 March 2011 and 4 March 2013) with high depolarization ratios (greater than 30 %) from the surface to 5–7 km above the ground associated with precipitation of ice particles and the presence of a supercooled liquid water (depolarization less than 10 %) clouds. Diamond dust and/or ice fog are detected during the cold and dry periods (5 April 2011 and 5 March 2013) with high depolarization ratios (greater than 30 %) in the planetary boundary layer to a maximum altitude of 100–300 m above the ground with little trace of precipitation. Considering 5-day back trajectories, we show that the thick cloud episodes are attributed to air masses with an oceanic origin whilst the diamond dust/ice fog episodes are attributed to air masses with continental origins. Although operational models can reproduce thick cloud episodes in the free troposphere, they cannot evaluate the diamond dust/ice fog episodes in the planetary boundary layer because they require to use more sophisticated cloud and aerosol microphysics schemes

Genesis of Diamond Dust and Thick Cloud Episodes observed above Dome C, Antarctica

<p><strong>Abstract.</strong> From 15 March to 8 April 2011 and from 4 to 5 March 2013, the atmosphere above Dome C (Concordia station, Antarctica, 75°06' S, 123°21' E, 3233 m amsl) has been probed by several instruments and model to study episodes of thick cloud and diamond dust (cloud constituted of suspended ice crystals). 1) A ground-based microwave radiometer (HAMSTRAD, H<sub>2</sub>O Antarctica Microwave Stratospheric and Tropospheric Radiometers) installed at Dome C that provided vertical profiles of tropospheric temperature and absolute humidity to calculate Integrated Water Vapour (IWV). 2) Daily radiosoundings launched at 12:00 UTC at Dome C. 3) A tropospheric aerosol Lidar that provides aerosol depolarization ratio along the vertical at Dome C. 4) Down- and upward short- and longwave radiations as provided by the Baseline Surface Radiation Network (BSRN) facilities. 5) Space-borne aerosol depolarization ratio from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) Lidar aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) platform along orbits close to the Dome C station. The time evolution of the atmosphere has also been evaluated by considering the outputs from the meso-scale AROME and the global-scale ARPEGE meteorological models. Two distinct periods are highlighted by all the datasets: the warm and wet periods (24–26 March 2011 and 4 March 2013) and the cold and dry periods (5 April 2011 and 5 March 2013). Combining radiation and active measurements of aerosols with nebulosity calculations, a thick cloud is detected during the warm and wet periods with high depolarization ratios (greater than 30 %) from the surface to 5–7 km altitude associated with precipitation of ice particles and the presence of a supercooled liquid water (depolarization of about 10 %) cloud. During the cold and dry periods, high depolarization ratios (greater than 30 %) to a maximum altitude of 100–500 m are measured suggesting that the cloud is constituted of ice crystals with no trace of precipitation. These ice crystals in suspension in the air are named diamond dust. Considering 5-day back trajectories from Dome C and global distributions of IWV over the Antarctic show that the thick-cloud episode is attributed to air masses with an oceanic origin whilst the diamond dust episode is attributed to air masses with continental origins. This is consistent with ARPEGE temperature and water vapour tendency favouring predominantly advection processes including microphysical processes for water vapour.</p&gt

Dataset of in-situ and remote sensing measurements of precipitation in the inner Antarctic (Dome-C 75°S 123°E) for the years 2014-2021

The database contains original data collected between 2014 and 2021 at the Concordia Station (Dome-C, Antarctica, 75°S, 123°E) using three automatic instruments: 1) A flatbed scanner (ICECAMERA) provides information on the shape and size of precipitation on an hourly basis. 2) An automatic depolarization LIDAR provides the height, structure and phase of the cloud that originated the precipitation on a 5-minute basis. The height range for the LIDAR is between 20 and 7000 meters. 3) A microwave radiometer (HAMSTRAD) provides the local temperature at the altitude where precipitation is formed. The combination of three instruments made it possible to 'label' each precipitation grain with its size, shape parameters, temperature, altitude of formation, and surface meteorological data. Each yearly DATA_YYYY.rar data set is organized into daily directories, where all valid LIDAR false color plots, HAMSTRAD data, and ICECAMERA images are collected, along with processed numerical data for all the ice grains collected. HYSPLIT back trajectories with Dome-C as the final point are also included. The dataset's content is explained in the data legend.doc file MATLAB models.rar includes multiple MATLAB Canonical and SVM models that automatically classify the type of cloud-originating precipitation (at Dome C) based on the relative abundance of different ice grain shapes. Details and instructions for their use can be found in the Legend for MATLAB classifiers.docx document

Unusual PSCs observed by LIDAR in Antarctica

International audiencePolar Stratospheric Cloud (PSC) measurements by ground‐based LIDAR were carried out at Dumont d'Urville, Antarctica, during the years 1989 to 1993. From such measurements it can be seen that there are cases of PSCs that are not consistent with the simplest nitric acid trihydrate (NAT) theories. Several cases of long‐lasting, non‐depolarizing PSCs were detected at temperatures below or close to the NAT freezing threshold, at about 195°K, suggesting the presence of durable supercooled droplets. PSC cases showing depolarizing (frozen) particles well above the NAT expected threshold are also shown. These results seems to be more consistent with recent laboratory and in situ findings, suggesting a close link between sulfate and PSC particles through the HNO3‐H2O‐H2SO4 ternary system. In this framework, non‐depolarizing clouds observed below and close to 195°K would arise from the uptake of HNO3 and water by the background particles before the freezing of the ternary system and the successive growth in nitric‐acid hydrates. Depolarizing “warm” PSCs are also consistent with the laboratory‐observed high melting point of the frozen sulfate core, that remains after NAT evaporation. A problematic PSC case, that cannot be easily explained by this theory is also shown

Antarctic ice cloud identification and properties using downwelling spectral radiance from 100 to 1400 cm-1

One year (2013) of high spectral resolution measurements of downwelling radiance in the 100\u20131,400 cm 121 range, taken by the Fourier Transform Spectrometer REFIR-PAD at the research station Concordia (Antarctic Plateau), is analyzed. Optically thin ice clouds are identified by means of a new identification/classification tool based on a Support Vector Machine algorithm. The use of transparent microwindow channels in the Far InfraRed (FIR) spectral region (100\u2013667 cm 121) is shown to be of great importance in the identification and classification of cloud type. In particular, the channels between 380 and 575 cm 121 are key channels for the clear/cloud and phase identification due to their sensitivity to cloud properties; in addition, FIR channels down to 238 cm 121 are exploited for the selection of precipitating or nonprecipitating cases because of their sensitivity also to water vapor content. A subset of 26 cases of nonprecipitating ice clouds is selected based on the presence of colocated LIDAR and radiosonde data. REFIR-PAD channel in the 800\u20131,000 cm 121 are used to derived optical and microphysical properties for four different assumptions concerning the crystal habits. Results, showing a correlation between cloud base temperature, optical depth, and particle size distribution effective dimensions, are compared with what found in literature. Based on the retrievals, forward simulations are also run over the whole sensor spectral interval, and results are compared to data. The simulation-data residuals in the FIR are evaluated for selected \u201cwindow\u201d channels and analyzed in relation to crystal's habit assumption, cloud retrieved features, and atmospheric water vapor content

Use of polarimetric lidar for the study of oriented ice plates in clouds

A polarization lidar operating at 532 nm was converted into an automatic, polarimetric lidar capable of measuring the entire Stokes vector of backscattered light and its derived quantities. Among these quantities, circular and linear depolarizations were studied as tools for investigating the presence of anisotropic scattering media. Isotropic scatterers show a simple relationship between linear and circular depolarization, a relation that we confirm theoretically and experimentally. Deviations from this relation, which are possible in the presence of anisotropic scatterers such as horizontally oriented ice plates when they are observed with a slant lidar, were studied both numerically and experimentally. © 2006 Optical Society of America

A data cluster analysis software for MATLAB 4.0

Consiglio Nazionale delle Ricerche (CNR). Biblioteca Centrale / CNR - Consiglio Nazionale delle RichercheSIGLEITItal