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

DIAMOND DETECTORS FOR CHARACTERIZATION OF LASER-GENERATED PLASMA

Abstract -CVD mono-crystalline diamond films were employed as detectors of the Introduction -Laser-generated plasma is characterized by high temperature and density

Fe and Fe+2%Si targets as ion sources via UV laser ablation plasma

In the last years the ion component of a laser-produced plasma has been considered and studied as an object to provide high-density ion sources, which can be applied in many fields such as laser-induced implantation. In this work a KrF laser beam of 108 W/cm2 irradiance was focused onto single-crystalline Fe and single-crystalline Fe with 2% of Si targets and the characteristics of both free expanding laser-produced plasmas were compared. The time-of-flight (TOF) method was applied to determine the ion charge yield at various laser fluences and the ion angular spread. The analyses of TOF spectra showed a synergetic effect of the silicon admixture in target material on the Fe ions production. Besides, this admixture was also responsible of the increasing of the plasma temperature which corresponds in turn to the increasing of the average kinetic energy of the particles as well as of the more collimated ion distribution

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