New estimations of precipitation and surface sublimation in East Antarctica from snow accumulation measurements

Surface mass balance (SMB) distribution and its temporal and spatial variability is an essential input parameter in mass balance studies. Different methods were used, compared and integrated (stake farms, ice cores, snow radar, surface morphology, remote sensing) at eight sites along a transect from Terra Nova Bay (TNB) to Dome C (DC) (East Antarctica), to provide detailed information on the SMB. Spatial variability measurements show that the measured maximum snow accumulation (SA) in a 15 km area is well correlated to firn temperature. Wind-driven sublimation processes, controlled by the surface slope in the wind direction, have a huge impact (up to 85% of snow precipitation) on SMB and are significant in terms of past, present and future SMB evaluations. The snow redistribution process is local and has a strong impact on the annual variability of accumulation. The spatial variability of SMB at the kilometre scale is one order of magnitude higher than its temporal variability (20–30%) at the centennial time scale. This high spatial variability is due to wind-driven sublimation. Compared with our SMB calculations, previous compilations generally over-estimate SMB, up to 65% in some areas.     

Tropospheric Ozone at High Latitudes in Clean and Polluted Air Masses, a Climatological Study

Several years of continuous measurements of surfaceozone at Norwegian monitoring sites are studied in aclimatological way. The monitoring sites are at rurallocations extending from 58°N, a few hundredkilometers from the European continent and into theArctic at 79°N. The ozone observations are sorted intoclasses of integrated NO_x emissions along 96 h backtrajectories. The average seasonal cycles of ozone areestimated for each class separately. The differencesindicate the change from the background air due toanthropogenic emissions. The average seasonal cycle ofozone in the cleanest air masses showed a maximum inspring and a minimum during summer and autumn at allsites, but the spring maximum was more pronounced atthe southernmost locations. Polluted air masses showedan ozone deficit during winter and a surplus duringsummer. The deviation from the background was clearlylinked to the integrated NO_x emission along thetrajectories. In summer the calculations indicate thatthe number of ozone molecules formed per NO_x moleculedrops with increasing emissions. The average seasonalcycle of ozone at Birkenes for different transportsectors indicate that the most pronounced ozoneformation takes place in air masses from E-Europe/Russia.     

Concentration and size variation of condensation nuclei at Mawson,Antarctica

Condensation nucleus (CN) concentrations have been measured at Mawson (67.6°S, 62.9°E) since mid 1981. Weekly median concentrations have an annual cycle with a maximum of around 300 to 400 cm^-3 in summer and a minimum of a few tens of particles per cm^-3 in winter. In this respect Mawson behaves very much like an Antarctic continental location. Preliminary measurements of the size distribution of CN particles taken over a nine month period suggest a seasonal change in typical particle radius from around 0.01 m in winter to around 0.04 m in summer. Diurnal variation in the CN concentration is generally very weak and does not show any systematic relation to the pronounced diurnal variation in wind-speed at Mawson.Department of Science, Antarctic Division     

Observed and Modelled Convective Mixing-Layer Height at Dome C,Antarctica

The mixing-layer height is estimated using measurements from a high resolution surface-layer sodar run at the French-Italian station of Concordia at Dome C, Antarctica during the summer 2011–2012. The temporal and spatial resolution of the sodar allows the monitoring of the mixing-layer evolution during the whole diurnal cycle, i.e. a very shallow nocturnal boundary layer followed by a typical daytime growth. The behaviour of the summer mixing-layer height, variable between about 10- and 300 m, is analyzed as a function of the mean and turbulent structure of the boundary layer. Focusing on convective cases only, the retrieved values are compared with those calculated using a one-dimensional prognostic equation. The role of subsidence is examined and discussed. We show that the agreement between modelled and experimental values significantly increases if the subsidence is not kept fixed during the day. A simple diagnostic equation, which depends on the time-averaged integral of the near-surface turbulent heat flux, the background static stability and the buoyancy parameter, is proposed and evaluated. The diagnostic relation performance is comparable to that of the more sophisticated prognostic model.     

Chemical composition of falling snow at Dumont d'Urville,Antarctica

Fourteen samples of fresh falling snow were collected at Antarctic coastal base Dumont d'Urville in 1984. The samples have been analysed for major ions (including MSA) by ion chromatography and acid titration. The results are relevant to the chemical composition of background precipitation in polar marine conditions. The seasalt aerosol contribution is dominant. All samples are found to be acidic in the range 3–16 eq/l. The calculated non-seasalt sulfate (nssSO₄ ^2-) concentration is significantly negative for 3 of the 14 samples. NssSO₄ ^2- is found to be relatively high in summer and fall. MSA also exhibits the same pattern probably linked to local marine biogenic activity and/or atmospheric photochemical processes. The MSA to nssSO₄ ^2- ratio is in good agreement with values reported for coastal Antarctic ice cores and subantarctic acrosol. The background mean value for nitrate concentration is 1.1 eq/l but two very strong spikes (up to 16 eq/l) are observed. The first seems to be linked with long range transport of continental air masses while the second (in winter) is clearly due to a sudden input of nitric acid, possibly from the stratosphere.This paper represents a preliminary approach to a larger air and snow monitoring to be developped at this site.     

南极中山站太阳紫外辐射测值比较

比较分析了2017年南极中山站3种仪器测量地面太阳紫外B（UVB）波段和紫外A（UVA）波段的辐照度。以Brewer光谱仪测值为参考,国产宽波段FSUVB日射表在UVB（波段280~315 nm）的辐照度相对误差为（55±75）%,误差随大气臭氧总量的增加呈上升趋势,但在南极“臭氧洞”期间偏低。Yankee UVB宽波段日射表在UVB（波段280~320 nm）的辐照度相对误差为（-31±22）%;国产宽波段FSUVA日射表在UVA（波段315~400 nm）的辐照度相对误差为（23±5.9）%。太阳天顶角低于80°的晴天以Tropospheric Ultraviolet Visible（TUV）辐射模式计算结果为参考时,FSUVB,Yankee UVB和FSUVA辐照度的平均相对误差分别为（30±37）%,（-22±19）%和（27±6.4）%,而Brewer相对误差未超过3.5%。国产宽波段UV日射表测值偏高,反映出波长较长的杂散光对太阳辐照度测值影响明显。     

One Year of Surface-Based Temperature Inversions at Dome C, Antarctica

In 2005 the Study of Stable Boundary Layer Environment at Dome C (STABLEDC) experimental campaign was conducted at the plateau station of Concordia at Dome C, Antarctica. Temperature profiles measured with a microwave radiometer were used to study the characteristics of surface-based temperature inversions over the course of a year. Statistics of temperature profiles for every month are discussed; the difference between daytime and nocturnal cases observed during the summer months disappears during winter. Surface-based temperature inversions occurred in 70 % of the time during summer, and almost all of the time during winter. During winter the occurrence of warming events leads to a decrease in the temperature difference between the top and the base of the inversion (i.e. the inversion strength). The inversion strength maxima ranged between $3\,^{\circ }\mathrm{C}$ (December) and $35\,^{\circ }\mathrm{C}$ (August) corresponding to gradients of 0.1 and $0.3\,^{\circ }\mathrm{C}\, \mathrm{m}^{-1}$ , respectively. The average surface-based inversion height presents a daily cycle during the summer months with values up to 200 m in the morning hours, while it affects a layer always deeper than 100 m during the winter months. The relationships between inversion strength and the downward longwave radiative flux, absolute temperature, and wind speed are examined. The inversion strength decreases as the longwave radiation increases. A clear anti-correlation between inversion strength and near-surface temperature is evident throughout the year. During the winter, the largest inversion strength values were observed under low wind-speed conditions; in contrast, a clear dependence was not found during the summer.     

Momentum- and Heat-Flux Parametrization at Dome C,Antarctica: A Sensitivity Study

An extensive meteorological observational dataset at Dome C, East Antarctic Plateau, enabled estimation of the sensitivity of surface momentum and sensible heat fluxes to aerodynamic roughness length and atmospheric stability in this region. Our study reveals that (1) because of the preferential orientation of snow micro-reliefs (sastrugi), the aerodynamic roughness length \(z_{0}\) varies by more than two orders of magnitude depending on the wind direction; consequently, estimating the turbulent fluxes with a realistic but constant \(z_{0}\) of 1 mm leads to a mean friction velocity bias of \(24\,\%\) in near-neutral conditions; (2) the dependence of the ratio of the roughness length for heat \(z_{0t}\) to \(z_{0}\) on the roughness Reynolds number is shown to be in reasonable agreement with previous models; (3) the wide range of atmospheric stability at Dome C makes the flux very sensitive to the choice of the stability functions; stability function models presumed to be suitable for stable conditions were evaluated and shown to generally underestimate the dimensionless vertical temperature gradient; as these models differ increasingly with increases in the stability parameter z / L, heat flux and friction velocity relative differences reached \(100\,\%\) when \(z/L > 1\); (4) the shallowness of the stable boundary layer is responsible for significant sensitivity to the height of the observed temperature and wind data used to estimate the fluxes. Consistent flux results were obtained with atmospheric measurements at heights up to 2 m. Our sensitivity study revealed the need to include a dynamical parametrization of roughness length over Antarctica in climate models and to develop new parametrizations of the surface fluxes in very stable conditions, accounting, for instance, for the divergence in both radiative and turbulent fluxes in the first few metres of the boundary layer.     

Measurements and Parametrizations of the Atmospheric Boundary-Layer Height at Dome C,Antarctica

An experimental campaign, Study of the Atmospheric Boundary Layer Environmental at Dome C, was held during 2005 at the French-Italian station of Concordia at Dome C. Ground-based remote sensors, as well as in situ instrumentation, were used during the experimental campaign. The measurements allowed the direct estimation of the polar atmospheric boundary-layer height and the test of several parametrizations for the unstable and stable boundary layers. During the months of January and February, weak convection was observed while, during the polar night, a long-lived stable boundary layer occurred continuously. Under unstable stratification the mixing-layer height was determined using the sodar backscattered echoes and potential temperature profiles. The two estimations are highly correlated, with the mixing height ranging between 30 and 350 m. A simple prognostic one-dimensional model was used to estimate the convective mixing-layer height, with the correlation coefficient between observations and model results being 0.66. The boundary-layer height under stable conditions was estimated from radiosounding profiles as the height where the critical Richardson number is reached; values between 10 and 150 m were found. A visual inspection of potential temperature profiles was also used as further confirmation of the experimental height; the results of the two methods are in good agreement. Six parametrizations from the literature for the stable boundary-layer height were tested. Only the parametrization that considers the long-lived stable boundary layer and takes into account the interaction of the stable layer with the free atmosphere is in agreement with the observations.     

Acoustic sounder measurements of the planetary boundary layer at Maitri,Antarctica

The planetary boundary layer (PBL) over the Indian Antarctic station, Maitri (70.7° S; 11.7° E; 120 m asl) has been studied using a monostatic acoustic sounder. Acoustic sounder records reveal that the Antarctic PBL remains stably stratified throughout the year except for some periods in the peak summer months. The summertime PBL exhibits a diurnal variation with ground-based inversions developing at night and the convective plumes occurring during the peak sunlight hours. The cyclonic inflow of warm oceanic air towards the continent's interior from the coast helps in the development of the elevated layers and the Kelvin-Helmholtz waves observed on the sodar records.     

南极长城站和中山站降水形态变化特征的研究

利用南极长城站1985—2015年和中山站1989—2015年的天气现象记录和日平均气温资料,分析两站降水、降雨和降雪日数的长期变化特征及其变化趋势,并讨论了长城站降水形态变化与当地气温和阿蒙森低压变化的联系。结果表明：长城站降水日数较多,年总降水日数为236~343 d,有增加的趋势,变化速率为4.51 d/10a;其中降雨日数为74~185 d,降雪日数为157~282 d,增加的速率分别为2.68 d/10a和1.25 d/10a。而中山站年降水日数较少,年总降水日数为104~173 d,有减小的趋势,变化速率为-1.30 d/10a,中山站全年气温几乎都在0℃以下,降雨稀少,降雪为主要的降水形态。长城站年平均气温和降雨日数与总降水日数的比值（雨日比）显著正相关,在增温速率较大的秋季（3—5月),雨日比也显著增加(4.36%/10a)。降水形态受气温的影响很大,随着气温升高,长城站年降水日数中降雨日数的比重增加。秋季阿蒙森低压经向中心的东移有利于暖湿气流吹向南极半岛,也促进了降雨的发生。     

Nitrogen and sulfur species in acrosols at Mawson,Antarctica, and their relationship to natural radionuclides

High volume aerosol samples were collected continuously at Mawson, Antarctica (67°36'S, 62°30'E), from February 1987 through October 1989. All samples were analyzed for Na⁺, Cl^-, SO₄ ⁼, NO₃ ^-, methanesulfonate (MSA), NH₄ ⁺,⁷Be, and²¹⁰Pb. The annual mean concentrations of many of the species are very low, substantially lower than even those over the relatively pristine regions of the tropical and subtropical South Pacific. The concentrations at Mawson are comparable both in magnitude and in seasonality to those which have been measured in long term studies at the South Pole and at the coastal German Antarctic research station, Georg von Neumayer (GvN). This comparability suggests that the aerosol composition may be relatively uniform over a broad sector of the Antarctic. The concentrations of most of the species exhibit very strong and sharply-defined seasonal cycles. MSA, non-sea-salt (nss) SO₄ ⁼ and NH₄ ⁺ all exhibit similar cycles, with maxima during the austral summer (December through February) being more than an order of magnitude higher than the winter minima. The limited⁷Be data appears to exhibit a similar cycle. Although nitrate and²¹⁰Pb also exhibit relatively high concentrations during the austral summer, their cycles are far more complex than those of the previous species with indications of multiple peaks. As expected, the concentration of sea-salt (as indicated by Na⁺ and Cl^-) peaks during the winter. The results from multiple variable regression analyses indicate that the dominant source of nss SO₄ ⁼ is the oxidation of dimethylsulfide (DMS) which produces MSA and nss SO₄ ⁼ in a ratio of about 0.31 (about five times higher than that over the tropical and subtropical oceans). However, a very significant fraction (about 25%) of the nss SO₄ ⁼ is associated with NO₃ ^-, The seasonal cycle of NO₃ ^- is similar to that of²¹⁰Pb and distinctly different from that of⁷Be and MSA. These results indicate that the major source of NO₃ ^- over Antarctica is probably continental as opposed to stratospheric or marine biogenic.     

Long-term Variability of Integral and Spectral Transparency of the Atmosphere at Mirny Observatory,Antarctica

The aerosol optical depth of the atmosphere obtained from spectral sun photometer measurements and the integral optical depth determined from standard actinometric observations of direct solar radiation are the parameters of the optical state of the atmosphere. The quantitative estimates of the integral transparency and aerosol optical depth of the atmosphere in Antarctica are presented, their long-term variability over the entire period of observations is analyzed. The comparison of obtained data with the estimates for other natural regions and conditions revealed that during the periods without the impact of volcanic eruptions, the levels of atmospheric aerosol turbidity in Antarctica over the recent decades are minimal on the planet and can be considered as global background characteristics.     

Atmospheric trace gas measurements at Palmer Station,Antarctica: 1982–83

In early 1982 a station capable of sampling atmospheric trace gas constituents on a continuous basis was established at Palmer Station, Anvers Island, adjacent to the Antarctic Peninsula (64° 46S 64° 04W). Sampling operations began about 1 February 1982. This is an initial report on this station, its location, equipment and general research objectives along with some initial sampling results. The constituents being measured and recorded were: ozone, methane, carbon dioxide, carbon monoxide, CCl₃F (fluorocarbon-11), CCl₂F₂ (fluorocarbon-12), carbontetrachloride, methylchloroform, nitrous oxide, and Aitken nuclei (CN). Data storage, data processing, and sampling system control is handled by a Hewlett-Packard 85 system. Preliminary analyses of about the first 20–22 months of data are presented and show not only the expected long-term trends but also shorter period concentration cycles that seem to be related to synoptic meteorology.     

Radiation observations at Aspendale,Australia, and their comparison with other data

Summary Results are presented of three years' measurements at Aspendale of net, global and diffuse radiation (R, G andD respectively) as well as of short-wave radiation on a north-facing surface (G _N ).The results are compared with other Australian radiation measurements, and the local character of the constants inÅngström type estimation formulae pointed out. A term is given which corrects such formulae by taking into account the uneven distribution of cloudiness over the day. The effect of orographic cloud on radiation is also discussed.After correction for climatological mean conditions, Aspendale summer values ofG are about 18% higher than those ofBlack [4] and ofBudyko [7]; the winter values agree reasonably. Summer and winter values ofR are considerably higher thanBudyko's—about 21% and 28% respectively. In addition some disagreement is found with the Australian Radiation Records 1953–1956.In winter, the amounts of diffuse and solar radiation (G-D) are about equal.

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Zusammenfassung Die Resultate dreijähriger Registrierungen der Strahlungsbilanz, der Global- und der Himmelsstrahlung (R, G undD) sowie der kurzwelligen Strahlung auf eine Nordwand (G _N ) werden mitgeteilt.Die Ergebnisse werden mit anderen australischen Strahlungsmessungen verglichen, und die örtliche Abhängigkeit der Konstanten in den vonÅngström angegebenen Formeln wird hervorgehoben. Es wird eine Korrekturgröße in die Formeln eingeführt, mit der der Einfluß der ungleichmäßigen Verteilung der Bewölkung über den Tag erfaßt werden kann. Ferner wird der Effekt der orographisch bedingten Bewölkung auf die Strahlungssummen diskutiert.Es ergibt sich, daß nach Anbringung einer Korrektur auf klimatologische Durchschnittsverhältnisse die Globalstrahlungswerte von Aspendale im Sommer ungefähr um 18% größer sind als die vonBlack [4] und vonBudyko [7] angegebenen Werte; die Winterwerte stimmen einigermaßen überein. Sommer- und Winterwerte vonR sind um ungefähr 21% und 28% größer alsBudykos Werte. Es wurden auch Unterschiede zwischenG und den Australian Radiation Records 1953–1956 festgestellt.Im Winter sind die Beträge der Himmels- und der Sonnenstrahlung (G-D) annähernd gleich.

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Résumé On décrit les résultats obtenus durant trois ans d'enregistrements du bilan du rayonnement, de la radiation globale et de celle du ciel (R, G etD), ainsi que du rayonnement d'ondes courtes reçu par une paroi exposée au nord (G _N ).Ces résultats sont alors comparés à d'autres mesures australiennes du rayonnement et l'on en tire la dépendance locale des constantes contenues dans les formules d'Ångström. On introduit ainsi un facteur de correction dans les dites formules. Ce facteur permet de tenir compte de l'influence des fluctuations de la nébulosité au cours de la journée. En outre, on discute les répercussions qu'ont les nuages orographiques sur les sommes de rayonnement.Il en résulte que, après l'application de la correction, les valeurs tirées des conditions climatologiques moyennes sont pour l'été, selon Aspendale, environ 18% supérieures à celles indiquées parBlack [4] et parBudyko [7], bien que les quantités hivernales correspondent à peu près. Les valeurs estivales et hivernales deR sont, elles, environ 21% et 28% plus importantes que celles deBudyko. On constate également une différence entreG et les «Australian Radiation Records» 1953–1956.Les valeurs de la radiation du ciel et du soleil (G-D) sont à peu près équivalentes en hiver.

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With 13 Figures