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A 10-year record of oxygen and hydrogen isotopic composition of precipitation is presented here: from 2008 to 2017, 1483 daily precipitation samples were collected year-round on a raised platform at Concordia Station, East Antarctica. Weather data were retrieved from the Italian Antarctic Meteo-Climatological Observatory automatic weather station (AWS), while ERA5 was used to estimate total precipitation. The δ –temperature relationships were moderately high for daily data (r2=0.63 and 0.64 for δ18 O and δ2 H, respectively) and stronger using monthly data (r2=0.82 for both δ18 O and δ2 H), with a slope of about 0.5 ‰ °C -1 for δ18O/TAWS (3.5 ‰ °C -1 for δ2H/TAWS), which remains consistent also using annual averages. The isotopic composition of precipitation is the input signal of the snow–ice system, and this dataset will be useful to improve the interpretation of paleoclimate records and promote a better understanding of the post-depositional processes affecting the isotopic signal in ice cores. This dataset represents a benchmark for the evaluation of isotope-enabled general circulation models. Here, the ECHAM6-wiso output was compared to experimental data, showing moderately good relationships for δ18 O and δ2 H but not for d-excess, nonetheless marking a substantial improvement from the previous release of the model. [ABSTRACT FROM AUTHOR]

Clouds in Antarctica are key elements that affect radiative forcing and thus Antarctic climate evolution. Although the vast majority of clouds are composed of ice crystals, a non-negligible fraction constitutes supercooled liquid water (SLW; water held in liquid form below 0 °C). Numerical weather prediction models have great difficulty in forecasting SLW clouds over Antarctica, favouring ice at the expense of liquid water and therefore incorrectly estimating the cloud radiative forcing. Remote-sensing observations of SLW clouds have been carried out for several years at Concordia Station (75° S, 123° E; 3233 m above mean sea level), combining active lidar measurements (SLW cloud detection) and passive HAMSTRAD microwave measurements (liquid water path, LWP). The present project aimed at in situ observations of SLW clouds using sondes developed by the company Anasphere, specifically designed for SLW content (SLWC) measurements. These SLWC sondes were coupled to standard meteorological pressure–temperature–humidity sondes from Vaisala and released under meteorological balloons. During the 2021–2022 summer campaign, 15 launches were made, of which 7 were scientifically exploitable above a height of 400 m above ground level, a threshold height imposed by the time the SLWC sonde takes to stabilize after launch. The three main outcomes from our analyses are as follows: (a) the first in situ observations so far of SLW clouds in Antarctica with SLWC sondes; (b) on average, the consistency of SLW cloud heights as observed by in situ sondes and remote-sensing lidar; and (c) the liquid water path (vertically integrated SLWC) deduced by the sondes being generally equal to or greater than the LWP remotely sensed by HAMSTRAD. In general, the SLW clouds were observed in a layer close to saturation (U > 80 %) or saturated (U ∼ 100 %–105 %) just below or at the lowermost part of the entrainment zone, or capping inversion zone, which exists at the top of the planetary boundary layer and is characterized by an inflection point in the potential temperature vertical profile. Our results are consistent with the theoretical view that SLW clouds form and remain at the top of the planetary boundary layer. [ABSTRACT FROM AUTHOR]

Clouds affect the Earth climate with an impact that depends on the cloud nature (solid and/or liquid water). Although the Antarctic climate is changing rapidly, cloud observations are sparse over Antarctica due to few ground stations and satellite observations. The Concordia station is located on the eastern Antarctic Plateau (75 ∘ S, 123 ∘ E; 3233 m above mean sea level), one of the driest and coldest places on Earth. We used observations of clouds, temperature, liquid water, and surface irradiance performed at Concordia during four austral summers (December 2018–2021) to analyse the link between liquid water and temperature and its impact on surface irradiance in the presence of supercooled liquid water (liquid water for temperature less than 0 ∘ C) clouds (SLWCs). Our analysis shows that, within SLWCs, temperature logarithmically increases from -36.0 to -16.0 ∘ C when liquid water path increases from 1.0 to 14.0 g m -2. The SLWC radiative forcing is positive and logarithmically increases from 0.0 to 70.0 W m -2 when liquid water path increases from 1.2 to 3.5 g m -2. This is mainly due to the downward longwave component that logarithmically increases from 0 to 90 W m -2 when liquid water path increases from 1.0 to 3.5 g m -2. The attenuation of shortwave incoming irradiance (that can reach more than 100 W m -2) is almost compensated for by the upward shortwave irradiance because of high values of surface albedo. Based on our study, we can extrapolate that, over the Antarctic continent, SLWCs have a maximum radiative forcing that is rather weak over the eastern Antarctic Plateau (0 to 7 W m -2) but 3 to 5 times larger over West Antarctica (0 to 40 W m -2), maximizing in summer and over the Antarctic Peninsula. [ABSTRACT FROM AUTHOR]

A ten-year record of oxygen and hydrogen isotopic composition of precipitation is here presented: from 2008 to 2017, 1483 daily precipitation samples were collected all-year round on a raised platform at Concordia Station, East Antarctica. Weather data were retrieved from the Italian Antarctic Meteo-Climatological Observatory AWS, while ERA5 was used to estimate total precipitation. The δ-temperature relationships were moderately high for daily data (r²=0.63 and 0.64 for δ18O and δ²H, respectively) and stronger using monthly data (r²=0.82 for both δ18O and δ²H), with a slope of about 0.5 ‰/°C for δ18O/TAWS (3.5 ‰/°C for δ18O/TAWS), which remains consistent also using annual averages. The isotopic composition of precipitation is the input signal of the snow/ice system and this dataset will be useful to improve the interpretation of paleoclimate records and promote a better understanding of the post-depositional processes affecting the isotopic signal in ice cores. Isotope-enabled GCM ECHAM6-wiso output for the isotopic composition of precipitation was also compared to experimental data, showing moderately good relationships for δ18O and δ²H, but not for d-excess, nonetheless marking a substantial improvement from the previous release of the model. [ABSTRACT FROM AUTHOR]

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. OCIS codes: 010.3640, 010.2940, 010.1310, 260.5430.

Clouds affect the Earth climate with an impact that depends on the cloud nature (solid/liquid water). Although the Antarctic climate is changing rapidly, cloud observations are sparse over Antarctica due to few ground stations and satellite observations. The Concordia station located on the East Antarctic Plateau (75°S, 123°E, 3233 m above mean sea level), one of driest and coldest places on Earth. We used observations of clouds, temperature, liquid water and surface radiation performed at Concordia during 4 austral summers (December 2018-2021) to analyse the link between liquid water and temperature and its impact on surface radiation the presence of supercooled liquid water (liquid water for temperature less than 0°C) clouds (SLWCs). Our analysis shows that, within SLWCs, temperature logarithmically increases from -36.0°C to -16.0°C when liquid water path increases from 1.0 to 14.0 g m-2, and SLWCs positively impact the net surface radiation, which logarithmically increases by 0.0 to 50.0 m-2 when liquid water path increases from 1.7 to 3.0 g m-2. We finally estimate that SLWCs have a great potential radiative impact over Antarctica whatever the season considered, up 5.0 W m-2 over the Eastern Antarctic Plateau and up to 30 W m-2 over the Antarctic Peninsula in summer. [ABSTRACT FROM AUTHOR]

A multiwavelength lidar operated in Sodankyla, Finland, during the European Arctic Stratospheric Ozone Experiment (December 1991-March 1992). It produced vertical profiles of stratospheric aerosols at four wavelengths. The determination of aerosol mean size distribution has been performed by use of extinction/backscattering ratios as obtained from lidar data processing at 355, 352, and 750 nm. Log-normal distributions of sulfuric particles with mode radiu of [r.sub.m] = 0.12-0.25 [[micro]meter] and corresponding widths of s = 2-1.6 have been retrieved as best fits of experimental data, in good agreement with i situ measurements. A successful attempt to derive bimodal log-normal distributions is also described, together with the experimental and theoretical problems involved.

Statistics on the occurrence of clear skies, ice and mixed-phase clouds over the Concordia station, in the Antarctic Plateau, are provided for multiple time scales and analysed in relation to simultaneous meteorological parameters measured at the surface. Results are obtained by applying a machine learning cloud identification and classification code (named CIC) to 4 years of measurements between 2012-2105 of down-welling high spectral resolution radiances, measured by the Radiation Explorer in the Far Infrared-Prototype for Applications and Development (REFIR-PAD) spectroradiometer. The CIC algorithm is optimized for Antarctic sky conditions (clear sky, ice clouds, and mixed-phase clouds) and results in a total hit rate of almost 0.98, where 1.0 is a perfect score. Scene truth is provided by LiDAR measurements that are concurrent with REFIR-PAD. The CIC approach demonstrates the key role of far infrared spectral measurements for clear/cloud discrimination and for cloud phase classification. Mean annual occurrences are 72.3%, 24.9% and 2.7% for clear sky, ice and mixed-phase clouds respectively, with an inter-annual variability of a few percent. The seasonal occurrence of clear sky shows a minimum in winter (66.8%) and maxima (75-76%) during intermediate seasons. In winter the mean surface temperature is about 9°C colder in clear conditions than when ice clouds are present. Mixed-phase clouds are observed only in the warm season; in summer they amount to more than one third of total observed clouds. Their occurrence is correlated with warmer surface temperatures. In the austral summer, the mean surface air temperature is about 5°C warmer when clouds are present than in clear sky conditions. This difference is larger during the night than in daylight hours, likely due to increased solar warming. A comparison of monthly mean results with cloud occurrence/fraction derived from gridded (Level-3) satellite products, from both passive and active sensors, emphasizes the difficulty of adequately inferring cloud/clear-sky properties in the Antarctic region and highlights the ability of the CIC/REFIR-PAD synergy to identify multiple cloud conditions and study their variability at different time scales. [ABSTRACT FROM AUTHOR]

A comprehensive analysis of the water budget over the Dome C (Concordia, Antarctica) station has been performed during the austral summer 2018-2019 as part of the Year of Polar Prediction (YOPP) international campaign. Thin (~ 100-m) supercooled liquid water (SLW) clouds have been detected and analysed using remotely sensed observations at the station (tropospheric depolarization LIDAR, microwave radiometer HAMSTRAD, net surface radiation from Baseline Surface Radiation Network, BSRN), radiosondes and using satellite observations (CALIOP/CALIPSO) combined with a specific configuration of the Numerical Weather Prediction model: ARPEGE-SH. Two case studies are used to illustrate this phenomenon. On 24 December 2018, the atmospheric planetary boundary layer (PBL) evolved following a typical diurnal variation, that is to say with a warm and dry mixing layer at local noon thicker than the cold and dry stable layer at local midnight. Our study showed that the SLW clouds were observed at Dome C within the entrainment and the capping inversion zones at the top of the PBL. ARPEGE-SH was not able to correctly estimate the ratio between liquid and solid water inside the clouds. The SLW content was always strongly underestimated in the studied cases. The lack of simulated SLW in the model impacted the net surface radiation that was 20-30 W m-2 higher in the BSRN observations than in the ARPEGE-SH calculations, mainly attributable to longwave downward surface radiation from BSRN being 50 W m-2 greater than that of ARPEGE-SH. On 20 December 2018, a warm and wet episode impacted the PBL with no clear diurnal cycle of the PBL top height. SLW cloud appearance coincided with the warm and wet event within the entrainment and capping inversion zones. The amount of liquid water measured by HAMSTRAD was ~ 20 times greater in this perturbed PBL than in the typical PBL. Since ARPEGE-SH was not able to accurately reproduce these SLW clouds, the discrepancy between the observed and calculated net surface radiation was even greater than in the typical PBL period, reaching + 50 W m-2, mainly attributable to longwave downward surface radiation from BSRN being 100 W m-2 greater than that of ARPEGE-SH. The absence of SLW clouds in NWPs over Antarctica may indicate an incorrect simulation of the radiative budget of the polar atmosphere. [ABSTRACT FROM AUTHOR]

One year (2013) of high spectral resolution measurements of downwelling radiance in the 100–1,400 cm−1 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 (100–667 cm−1) is shown to be of great importance in the identification and classification of cloud type. In particular, the channels between 380 and 575 cm−1 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−1 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 800–1,000 cm−1 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 "window" channels and analyzed in relation to crystal's habit assumption, cloud retrieved features, and atmospheric water vapor content. Key Points: Spectral radiance measurements in the far infrared are used for cloud identification/classificationCloud properties are retrieved [ABSTRACT FROM AUTHOR]

An air ion spectrometer (AIS) was deployed for the first time at the Concordia station at Dome C (75°060 S, 123°230 E; 3220ma:s:l:), Antarctica during the period 22 December 2010-16 November 2011 for measuring the number size distribution of air ions.O In this work, we present results obtained from this air ion data set together with aerosol particle and meteorological data. The main processes that modify the number size distribution of air ions during the measurement period at this high-altitude site included new particle formation (NPF, observed on 85 days), wind-induced ion formation (observed on 36 days), and ion production and loss associated with cloud/fog formation (observed on 2 days). For the subset of days when none of these processes seemed to operate, the concentrations of cluster ions (0.9-1.9 nm) exhibited a clear seasonality, with high concentrations in the warm months and low concentrations in the cold. Compared to event-free days, days with NPF were observed with higher cluster ion concentrations. A number of NPF events were observed with restricted growth below 10 nm, which were termed as suppressed NPF. There was another distinct feature, namely a simultaneous presence of two or three separate NPF and subsequent growth events, which were named as multi-mode NPF events. Growth rates (GRs) were determined using two methods: the appearance time method and the mode fitting method. The former method seemed to have advantages in characterizing NPF events with a fast GR, whereas the latter method is more suitable when the GR was slow. The formation rate of 2 nm positive ions (JC 2) was calculated for all the NPF events for which a GR in the 2-3 nm size range could be determined. On average, JC 2 was about 0.014 cm-3 s-1. The ion production in relation to cloud/fog formation in the size range of 8-42 nm seemed to be a unique feature at Dome C, which has not been reported elsewhere. These ions may, however, either be multiply charged particles but detected as singly charged in the AIS, or be produced inside the instrument, due to the breakage of cloud condensation nuclei (CCN), possibly related to the instrumental behaviour under the extremely cold condition. For the wind-induced ion formation, our observations suggest that the ions originated more likely from atmospheric nucleation of vapours released from the snow than from mechanical charging of shattered snow flakes and ice crystals. [ABSTRACT FROM AUTHOR]