Supercooled liquid water cloud observed, analysed, and modelled at the top of the planetary boundary layer above Dome C, Antarctica

Abstract. 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 deep) supercooled liquid water (SLW) clouds have been detected and analysed using remotely sensed observations at the station (tropospheric depolarization lidar, the H2O Antarctica Microwave Stratospheric and Tropospheric Radiometer (HAMSTRAD), net surface radiation from the Baseline Surface Radiation Network (BSRN)), radiosondes, and satellite observations (CALIOP, Cloud-Aerosol LIdar with Orthogonal Polarization/CALIPSO, Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations) combined with a specific configuration of the numerical weather prediction model: ARPEGE-SH (Action de Recherche Petite Echelle Grande Echelle – Southern Hemisphere). The analysis shows that SLW clouds were present from November to March, with the greatest frequency occurring in December and January when ∼50 % of the days in summer time exhibited SLW clouds for at least 1 h. 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, which 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 with the liquid water path (LWP) strongly underestimated by a factor of 1000 compared to observations. 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 the BSRN longwave downward surface radiation being 50 W m−2 greater than that of ARPEGE-SH. The second case study took place on 20 December 2018, when a warm and wet episode impacted the PBL with no clear diurnal cycle of the PBL top. SLW cloud appearance within the entrainment and capping inversion zones coincided with the warm and wet event. 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 case, reaching +50 W m−2, mainly attributable to the downwelling longwave surface radiation from BSRN being 100 W m−2 greater than that of ARPEGE-SH. The model was then run with a new partition function favouring liquid water for temperatures below −20 down to −40 ∘C. In this test mode, ARPEGE-SH has been able to generate SLW clouds with modelled LWP and net surface radiation consistent with observations during the typical case, whereas, during the perturbed case, the modelled LWP was 10 times less than the observations and the modelled net surface radiation remained lower than the observations by ∼50 W m−2. Accurately modelling the presence of SLW clouds appears crucial to correctly simulate the surface energy budget over the Antarctic Plateau

Quantitative precipitation estimation over antarctica using different ze-sr relationships based on snowfall classification combining ground observations

Snow plays a crucial role in the hydrological cycle and energy budget of the Earth, and remote sensing instruments with the necessary spatial coverage, resolution, and temporal sampling are essential for snowfall monitoring. Among such instruments, ground-radars have scanning capability and a resolution that make it possible to obtain a 3D structure of precipitating systems or vertical profiles when used in profiling mode. Radars from space have a lower spatial resolution, but they provide a global view. However, radar-based quantitative estimates of solid precipitation are still a challenge due to the variability of the microphysical, geometrical, and electrical features of snow particles. Estimations of snowfall rate are usually accomplished using empirical, long-term relationships between the equivalent radar reflectivity factor (Ze) and the liquid-equivalent snowfall rate (SR). Nevertheless, very few relationships take advantage of the direct estimation of the microphysical characteristics of snowflakes. In this work, we used a K-band vertically pointing radar collocated with a laser disdrometer to develop Ze-SR relationships as a function of snow classification. The two instruments were located at the Italian Antarctic Station Mario Zucchelli. The K-band radar probes the low-level atmospheric layers, recording power spectra at 32 vertical range gates. It was set at a high vertical resolution (35 m), with the first trusted range gate at a height of only 100 m. The disdrometer was able to provide information on the particle size distribution just below the trusted radar gate. Snow particles were classified into six categories (aggregate, dendrite aggregate, plate aggregate, pristine, dendrite pristine, plate pristine). The method was applied to the snowfall events of the Antarctic summer seasons of 2018–2019 and 2019–2020, with a total of 23,566 min of precipitation, 15.3% of which was recognized as showing aggregate features, 33.3% dendrite aggregate, 7.3% plates aggregate, 12.5% pristine, 24% dendrite pristine, and 7.6% plate pristine. Applying the appropriate Ze-SR relationship in each snow category, we calculated a total of 87 mm water equivalent, differing from the total found by applying a unique Ze-SR. Our estimates were also benchmarked against a colocated Alter-shielded weighing gauge, resulting in a difference of 3% in the analyzed periods

Efecto del manejo y del temperamento animal sobre indicadores de calidad de la carne bovina

The aim of this research was to study the effect of different handling conditions on physiological stress indicators and meat quality of beef cattle by studying animals with different temperaments. Forty animals classified by their temperament (calm and disturbed) were used. They were fed on pastures and finished with a mixed diet of corn grain and pasture. Biochemical indicators of animal stress were measured at slaughter (packed cell volume -PCV-, proteins, glucose, creatinine, alkaline phosphatase -APactivity, cortisol, insulin, glycogen). Also, ultimate pH and instrumental colour were chosen as meat quality markers. Animal temperament showed a significantly increase (p<0.05) on PCV levels and a significantly (p<0.05) decrease on muscle glycogen. Besides, levels of plasma glucose and total proteins showed significant (p<0.05) differences associated to management applied. Meat quality markers (pH and colour) did not show significant differences according to handling conditions or temperament. Mean cortisol levels at the exsanguination time were significantly higher (p<0.05) than the values obtained one week prior to slaughter, which suggests an important effect of stress associated to slaughter procedures. It would be interesting to focus attention on the assessment of acute stress at abattoir, in order to improve handling protocols, and therefore to assure meat quality in Argentinean beef production systems.El objetivo del presente trabajo fue estudiar el efecto de diferentes condiciones de manejo sobre indicadores fisiológicos de estrés y de calidad de carne en bovinos con temperamentos contrastantes. Se utilizaron cuarenta animales clasificados como calmos y excitables. Los mismos fueron alimentados inicialmente a base de pasturas y terminados con una dieta mixta de grano de maíz y pasturas. Se dosaron indicadores bioquímicos de estrés (hematocrito, proteínas plasmáticas, glucosa, creatinina, actividad fosfatasa alcalina, cortisol, insulina, contenido muscular de glucógeno). Como indicadores de calidad de carne se midieron el pH de 24 h y color instrumental. El temperamento animal demostró un incremento significativo (p<0,05) en los niveles de hematocrito y con una disminución significativa (p<0,05) del glucógeno muscular. Los niveles de glucemia y de proteínas totales mostraron modificaciones significativas (p<0,05) asociadas con el manejo. El incremento (p<0,05) en los niveles plasmáticos de cortisol durante la faena, independientemente del tratamiento o el temperamento animal, sugiere un importante efecto estresor por parte del proceso de faena. Sería interesante centrar la atención en el estudio del estrés agudo, a fin de mejorar protocolos de manejo animal, y consecuentemente, optimizar la calidad de la carne asociada en los sistemas de producción de Argentina.Fil: Pighin, D. G.. Instituto Nacional de Tecnología Agropecuaria. Centro Nacional de Investigaciones Agropecuarias. Centro de Investigación de Agroindustrias. Instituto de Tecnología de Alimentos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Moron; ArgentinaFil: Davies, P.. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Grigioni, Gabriela Maria. Instituto Nacional de Tecnología Agropecuaria. Centro Nacional de Investigaciones Agropecuarias. Centro de Investigación de Agroindustrias. Instituto de Tecnología de Alimentos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Moron; ArgentinaFil: Pazos, A. A.. Instituto Nacional de Tecnología Agropecuaria. Centro Nacional de Investigaciones Agropecuarias. Centro de Investigación de Agroindustrias. Instituto de Tecnología de Alimentos; Argentina. Universidad de Moron; ArgentinaFil: Ceconi, I.. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Mendez, Diego Eduardo. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Buffarini, M.. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Sancho, A.. Instituto Nacional de Tecnología Agropecuaria. Centro Nacional de Investigaciones Agropecuarias. Centro de Investigación de Agroindustrias. Instituto de Tecnología de Alimentos; Argentina. Universidad de Moron; ArgentinaFil: Gonzalez, Claudia Beatriz. Instituto Nacional de Tecnología Agropecuaria. Centro Nacional de Investigaciones Agropecuarias. Centro de Investigación de Agroindustrias. Instituto de Tecnología de Alimentos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentin

The Impact of Precipitation and Sublimation Processes on Snow Accumulation: Preliminary Results

The need for climate change prediction has focused attention on the Surface Mass Balance (SMB) of the Antarctic continent and on how it influences the sea level. The SMB of the Antarctic plateau is governed by the equilibrium between precipitation and ablation processes such as sublimation and wind-borne snow redistribution. At scales of hundreds of kilometres snowfall variability dominates the snow accumulation process (Dery and Yau, 2002); at smaller scales, postdepositional process such as wind-borne redistribution, surface sublimation and snowdrift sublimation becomes more important. In recent years the sublimation phenomenon has received much attention from the glacial-meteorological community, and some theoretical studies have tried to model it (Bintanja, 1998; Dery & Yau, 2001b; Frezzotti, 2004). There are two different types of sublimation: surface sublimation and blowing snow sublimation. Surface sublimation is mostly determined by the continual exchange of water between the air (in the vapour phase) and the snow pack (in the solid phase) due to solar irradiance. Blowing snow sublimation is possibly the more effective of the two sublimation processes. It occurs when snow particles at the surface are blown by winds exceeding a certain threshold value. Particles suspended in the sub saturated Atmospheric Boundary Layer (ABL) sublimate at a relatively fast rate, cooling air mass transported by the wind and increasing the local atmospheric moisture content. When the first few meters of the ABL are completely saturated, the process is dumped. It takes a long time to meet this condition because katabatic winds transport saturated air masses to the coast, thereby reactivating sublimation. The role of sublimation in snow accumulation and its high variability at local scales are not fully understood due to the few available measurements in Antarctica. Further study and field experiments are required

The influence of the synoptic regime on stable water isotopes in precipitation at Dome C, East Antarctica

Abstract. The correct derivation of paleotemperatures from ice cores requires exact knowledge of all processes involved before and after the deposition of snow and the subsequent formation of ice. At the Antarctic deep ice core drilling site Dome C, a unique data set of daily precipitation amount, type, and stable water isotope ratios is available that enables us to study in detail atmospheric processes that influence the stable water isotope ratio of precipitation. Meteorological data from both automatic weather station and a mesoscale atmospheric model were used to investigate how different atmospheric flow patterns determine the precipitation parameters. A classification of synoptic situations that cause precipitation at Dome C was established and, together with back-trajectory calculations, was utilized to estimate moisture source areas. With the resulting source area conditions (wind speed, sea surface temperature, and relative humidity) as input, the precipitation stable isotopic composition was modeled using the so-called Mixed Cloud Isotope Model (MCIM). The model generally underestimates the depletion of 18O in precipitation, which was not improved by using condensation temperature rather than inversion temperature. Contrary to the assumption widely used in ice core studies, a more northern moisture source does not necessarily mean stronger isotopic fractionation. This is due to the fact that snowfall events at Dome C are often associated with warm air advection due to amplification of planetary waves, which considerably increases the site temperature and thus reduces the temperature difference between source area and deposition site. In addition, no correlation was found between relative humidity at the moisture source and the deuterium excess in precipitation. The significant difference in the isotopic signal of hoarfrost and diamond dust was shown to disappear after removal of seasonality. This study confirms the results of an earlier study carried out at Dome Fuji with a shorter data set using the same methods

A Nine-year series of daily oxygen and hydrogen isotopic composition of precipitation at Concordia station, East Antarctica

The atmospheric processes determining the isotopic composition of precipitation on the Antarctic plateau are yet to be fully understood, as well as the post-depositional processes altering the snow pristine isotopic signal. Improving the comprehension of these physical mechanisms is of crucial importance for interpreting the isotopic records from ice cores drilled in the low accumulation area of Antarctica, e.g., the upcoming Beyond EPICA drilling at Little Dome C. Up to now, few records of the isotopic composition of precipitation in Antarctica are available, most of them limited in time or sampling frequency. Here we present a 9-year long δ18O and δD record (2008-2016) of precipitation at Concordia base, East Antarctica. The snow is collected daily on a raised platform (1 m), positioned in the clean area of the station; the precipitation collection is still being carried out each year by the winter over personnel. A significant positive correlation between isotopes in precipitation and 2-m air temperature is observed at both seasonal and interannual scale; the lowest temperature and isotopic values are usually recorded during winters characterized by a strongly positive Southern Annular Mode index. To improve the understanding of the mechanisms governing the isotopic composition of precipitation, we compare the isotopic data of Concordia samples with on-site observations, meteorological data from the Dome C AWS of the University of Wisconsin-Madison, as well as with high-resolution simulation results from the isotope-enabled atmospheric general circulation models ECHAM5-wiso and ECHAM6-wiso, nudged with the ERA-Interim and ERA5 reanalyses respectively

Galacturonosyltransferase 4 silencing alters pectin composition and carbon partitioning in tomato

Pectin is a main component of the plant cell wall and is the most complex family of polysaccharides in nature. Its composition is essential for the normal growth and morphology pattern, as demonstrated by pectin-defective mutant phenotypes. Besides this basic role in plant physiology, in tomato, pectin structure contributes to very important quality traits such as fruit firmness. Sixty-seven different enzymatic activities have been suggested to be required for pectin biosynthesis, but only a few genes have been identified and studied so far. This study characterized the tomato galacturonosyltransferase (GAUT) family and performed a detailed functional study of the GAUT4 gene. The tomato genome harbours all genes orthologous to those described previously in Arabidopsis thaliana, and a transcriptional profile revealed that the GAUT4 gene was expressed at higher levels in developing organs. GAUT4-silenced tomato plants exhibited an increment in vegetative biomass associated with palisade parenchyma enlargement. Silenced fruits showed an altered pectin composition and accumulated less starch along with a reduced amount of pectin, which coincided with an increase in firmness. Moreover, the harvest index was dramatically reduced as a consequence of the reduction in the fruit weight and number. Altogether, these results suggest that, beyond its role in pectin biosynthesis, GAUT4 interferes with carbon metabolism, partitioning, and allocation. Hence, this cell-wall-related gene seems to be key in determining plant growth and fruit production in tomato

Supercooled liquid water clouds observed over Dome C, Antarctica: temperature sensitivity and cloud radiative forcing

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.</p