Assessment of spectral UV radiation at Marambio Base, Antarctic Peninsula

This study aims to assess the dependence of spectral UV radiation on different atmospheric and terrestrial factors, including solar zenith angle, ozone, and cloud cover, in the southern polar environment. For this purpose, 23 260 spectra (300–363 nm), obtained by the B199 Mk-III Brewer spectrophotometer at Marambio Base, Antarctic Peninsula region, over the period 2010–2020, were studied. A neural network model was developed to investigate the effects of the explanatory variables at 127 wavelengths in the interval 300–363 nm, with a 0.5 nm sampling interval. Solar zenith angle (SZA) proved to be the most important parameter, followed by cloud cover, total ozone column (TOC), and surface albedo. The relative SZA effect is greatest at the shortest wavelengths, where a 1∘ decrease in SZA results in a 6 %–18 % increase in UV irradiance (305 nm). TOC particularly affects the short wavelengths below approximately 320–325 nm, when for example at 305 nm a 10 DU decrease in TOC causes a 7 %–13 % increase in UV irradiance. The large-scale ozone holes (e.g., in 2011–2012, 2014–2015, 2018–2019) caused the spectral UV irradiance at very short wavelengths to peak in spring, whereas in other seasons (e.g., 2010–2011, 2012–2013), the maxima at all wavelengths were recorded in summer (November to January). Absorption of UV radiance by the ozone also affected the temporal distribution of very high spectral UV irradiances (i.e., highest 10 % of the distribution), when at 305 nm they were observed both in spring and summer months, and at 340 nm they occurred mostly in summer. The effect of cloud cover was strongest near the fully cloudy sky and in the summer months, when the Antarctic clouds tend to be thickest.</p

Multiply charged ions from iodine laser-produced plasma of medium- and high-Z targets

Maximum charge states of ions registered in the far expansion zone from laser-produced plasma of Al, Co, Ni, Cu, Ta, W, Pt, Au, Pb, and Bi are presented. The Thomson parabola spectrometer was used to display a general view of the ion species of an expanding plasma while detailed ion charge-energy spectra were determined by the cylindrical electrostatic ion energy analyzer. The current densities of highly charged ion groups above 20 mA/cm2 were measured by use of an ion collector at a distance of 1 m from the target. The photodissociation iodine laser system PERUN (λ = 1.315 μm, power density up to 1015 W cm−2) was employed as a drive

Ion production by lasers using high-power densities in a near infrared region

Results are presented of experiments on ion production from Ta targets using a short pulse (350-600 ps in focus) illumination with focal power densities exceeding 1014 Wcm-2 at the wavelength of an iodine photodissociation laser (1.315 μm) and its harmonics. Strong evidence of the existence of tantalum ions with the charge state +45 near the target surface was obtained by X-ray spectroscopy methods. The particle diagnostics point to the existence of frozen high charge states (4 MeV) for the highest observed charge states. A tentative theoretical explanation of the observed anomalous charge state freezing phenomenon in the expanding plasma produced by a subnanosecond laser pulse is give

Snow cover in the vicinity of the Arctowski Station (South Shetland Islands, Antarctic) in the period 1978-1996

Pokrywa śnieżna jest istotnym czynnikiem klimatotwórczym. Długość jej zalegania oraz jej miąższość wpływają również na wegetację roślinną i przebieg procesów peryglacjalnych w gruncie (Krajewski 1986; Kejna i Laska 1999b). W klimacie subantarktycznym pokrywa śnieżna tworzy się w warunkach ogromnej zmienności pogody. We wszystkich porach roku występują dodatnie i ujemne temperatury powietrza oraz stałe i ciekłe opady atmosferyczne. Silne wiatry przenoszą śnieg, znacznie modyfikując pokrywę śnieżną. Na Stacji H. Arctowskiego (Wyspa Króla Jerzego, Szetlandy Południowe) prowadzono systematyczne pomiary miąższości i czasu zalegania pokrywy śnieżnej w latach 1978-1990 oraz w 1992 i 1996 r. Jednak pokrywie śnieżnej poświęcono tylko niezbyt obszerne akapity w artykułach podsumowujących kolejne wyprawy, np. Nowosielski 1980; Kratke i Wielbińska 1981; Kowalski 1986; Kejna i Laska 1997. Zagadnienie to nie było poruszane nawet w opracowaniach o charakterze monografii klimatu tego obszaru, np. Marsz i Rakusa-Suszczewski 1986; Marsz i Styszyńska 2000. Badania nad zróżnicowaniem przestrzennym miąższości pokrywy śnieżnej w okolicach Stacji H. Arctowskiego oraz na Lodowcu Ekologii prowadzono jedynie w 1991 r. (Gonera i Rachlewicz 1997) oraz w 1996 r. (Caputa i in. 1997).The snow cover was investigated at the Arctowski Station (King George Island, Antarctic) in the period 1978-1996. During the 20th Polish Antarctic Expedition in 1996 the snow cover was measured in 32 places on the Sile of Special Scientific Interest No. 8 in the vicinity of the Arctowski Station (King George Island, Antarctic). On the King George Island the snow cover can occur around the year. In the summer months the snow cover is unstable. On the average 230 days with snow cover occurred at the Arctowski Station. The permanent snow cover began at 7th May and ended at 23th November. The mean snow cover thickness in the years 1978-1996 was between 40 to 50 cm, but the maximum reached 131 cm in 1980. The accumulation of snow was disturbed by frequent midwinter thawing and snow drift. In 1996 at the Arctowski Station permanent snow cover was formed on 6 June and stayed till 31 October. It reached its maximal thickness, 73 cm in September. The snow cover on the SSSI No 8 area showed great spatial differentiation. This is the effect not only the different sums of precipitation, but also the redistribution of the snow by wind. On the nonglaciated area the biggest thickness of snow cover was measured in depressions, in the filled up valleys of streams and on the snow patches. Heights and mountain peaks are without snow because of the wind. On the Ecology Glacier in 1996 the thickness of snow cover increased with the altitude. The biggest thickness of snow cover (177 cm) was measured at 165 m above sea level. In summer the snow cover melts, on the glaciers the snow border runs from 150 to 300 m above sea level in dependence on the weather conditions. On the nonglaciated areas the snow stays until the middle of summer in the form of snow patches

Reconstruction and analysis of erythemal UV radiation time series from Hradec Králové (Czech Republic) over the past 50 years

This paper evaluates the variability of erythemal ultraviolet (EUV) radiation from Hradec Králové (Czech Republic) in the period 1964–2013. The EUV radiation time series was reconstructed using a radiative transfer model and additional empirical relationships, with the final root mean square error of 9.9 %. The reconstructed time series documented the increase in EUV radiation doses in the 1980s and the 1990s (up to 15 % per decade), which was linked to the steep decline in total ozone (10 % per decade). The changes in cloud cover were the major factor affecting the EUV radiation doses especially in the 1960s, 1970s, and at the beginning of the new millennium. The mean annual EUV radiation doses in the decade 2004–2013 declined by 5 %. The factors affecting the EUV radiation doses differed also according to the chosen integration period (daily, monthly, and annually): solar zenith angle was the most important for daily doses, cloud cover, and surface UV albedo for their monthly means, and the annual means of EUV radiation doses were most influenced by total ozone column. The number of days with very high EUV radiation doses increased by 22 % per decade, the increase was statistically significant in all seasons except autumn. The occurrence of the days with very high EUV doses was influenced mostly by low total ozone column (82 % of days), clear-sky or partly cloudy conditions (74 % of days) and by increased surface albedo (19 % of days). The principal component analysis documented that the occurrence of days with very high EUV radiation doses was much affected by the positive phase of North Atlantic Oscillation with an Azores High promontory reaching over central Europe. In the stratosphere, a strong Arctic circumpolar vortex and the meridional inflow of ozone-poor air from the southwest were favorable for the occurrence of days with very high EUV radiation doses. This is the first analysis of the relationship between the high EUV radiation doses and macroscale circulation patterns, and therefore more attention should be given also to other dynamical variables that may affect the solar UV radiation on the Earth surface

Unusual biogenic calcite structures in two shallow lakes, James Ross Island, Antarctica

The floors of two shallow endorheic lakes, located on volcanic surfaces on James Ross Island, are covered with calcareous organosedimentary structures. Their biological and chemical composition, lake water characteristics, and seasonal variability of the thermal regime are introduced. The lakes are frozen down to the bottom for 8–9 months a year and their water chemistry is characterised by low conductivity and neutral to slightly alkaline pH. The photosynthetic microbial mat is composed of filamentous cyanobacteria and microalgae that are considered to be Antarctic endemic species. The mucilaginous black biofilm is covered by green spots formed by a green microalga and the macroscopic structures are packed together with fine material. Thin sections consist of rock substrate, soft biofilm, calcite spicules and mineral grains originating from different sources. The morphology of the spicules is typical of calcium carbonate monocrystals having a layered structure and specific surface texture, which reflect growth and degradation processes. The spicules' chemical composition and structure correspond to pure calcite. The lakes' age, altitude, morphometry, geomorphological and hydrological stability, including low sedimentation rates, together with thermal regime predispose the existence of this community. We hypothesise that the precipitation of calcite is connected with the photosynthetic activity of the green microalgae that were not recorded in any other lake in the region. This study has shown that the unique community producing biogenic calcite spicules is quite different to any yet described