bluuebunny/crossref_metadata_2025_split huggingface dataset:
First ground-based optical analysis of H&lt;sub&gt;β&lt;/sub&gt; Doppler profiles close to local noon in the cusp
Authors: Robertson S. C. , Lanchester B. S. , Galand M. , Lummerzheim D. , Stockton-Chalk A. B. , Aylward A. D. , Furniss I. , Baumgardner J. 
Published: June 2010

Abstract. Observations of hydrogen emissions along the magnetic zenith at Longyearbyen (78.2 N, 15.8 E geographic) are used to investigate the energy and source of protons precipitating into the high latitude region. During the hours around local solar noon (11:00 UT), measurements of the hydrogen Balmer β line are severely affected by sunlight, such that most data until now have been disregarded during these times. Here we use a simple technique to subtract sunlight contamination from such spectral data. An example is shown in which the removal of twilight contamination reveals a brightening of Hβ aurora over Svalbard on 27 November 2000 between 08:00 UT and 10:00 UT, which is centred on magnetic noon (08:48 UT). These data were measured by the High Throughput Imaging Echelle Spectrograph (HiTIES), one instrument on the Southampton-UCL Spectrographic Imaging Facility (SIF). Data from the IMAGE satellite confirms the location of a cusp "spot" over Svalbard at the time of the ground-based measurements, which moved in response to changes in the IMF conditions. A coincident pass of the DMSP F12 satellite provided input spectra for modelling studies of the Hβ profiles, which confirm that the method for removing the twilight contamination is robust. The results described here are the first ground-based optical measurements of Hβ Doppler profiles from the cusp region close to local solar noon, when scattered sunlight swamps the raw data.
Magnetoconjugate phenomena in Alaska and Macquarie Is., Australia in 2003: position of the global maximum iso-aurorae
Authors: Hajkowicz L. A. 
Published: June 2010

Abstract. An extensive magnetometer network in Alaska and Canada (consisting of 6 auroral and sub-auroral stations) and at Macquarie Is. (Australia) was used to study magnetoconjugate phenomena in 2003, using the H-component magnetograms. Altogether 193 magnetically disturbed days (with ΣKp≥10) were used in the analysis. The maximum negative swing in the H-component (ΔH) was assigned for each day from the auroral conjugate station's data. Two types of magnetoconjugate data were found: Type-1 when the daily (00:00–24:00 h UT) substorm activity was faithfully reproduced in the H-component variations in the northern and southern auroral zones, and Type-2 when a major peak in disturbance was largely missing in one conjugate location. A distinct maximum in the occurrence of the Type-1 events was in the southern summer (northern winter), reaching almost 70 per cent of cases. A minimum in this type of events was in the southern autumn and winter (around 40%). The correlation between ΣKp and ΔH for auroral stations faithfully reproduced the percentage occurrence of the Type-1 events for various seasons, with the maximum correlation coefficient r≈0.8 in summer. The time conjugacy of the events (i.e. the events occurring with a small time displacement in the southern and northern auroral zones) was highest for the auroral stations located close to the theoretical conjugate point location at L-value ≈ 5 (i.e. College and Macquarie Is.). The substorm onsets started earlier at the stations positioned east of the conjugate point of Macquarie Is. in spring and winter, indicating a westward drift of auroral disturbance with velocities of 1.4–1.6 km/s. The magnitude of average ΔH increased rapidly past the invariant latitude of Macquarie Is. towards the latitude of its nearest northern conjugate station College , particularly in spring. The average level of disturbance was consistently lower by about 30% at Macquarie Is. than at College. Since Macquarie Is. is the only available auroral station in the southern auroral zone the maximum southern auroral activity level (maximum iso-aurorae) should be inferred from magnetic data obtained at a northern conjugate station positioned at a slightly higher L-value, such as College (L-value = 5.73). It is concluded from the above considerations that the maximum iso-aurorae is located at a shell with L-value ≥ 5.73 in both hemispheres.
Cluster observations of reconnection due to the Kelvin-Helmholtz instability at the dawnside magnetospheric flank
Authors: Nykyri K. , Otto A. , Lavraud B. , Mouikis C. , Kistler L. M. , Balogh A. , Rème H. 
Published: June 2010

Abstract. On 3 July 2001, the four Cluster satellites traversed along the dawnside magnetospheric flank and observed large variations in all plasma parameters. The estimated magnetopause boundary normals were oscillating in the z-direction and the normal component of the magnetic field showed systematic 2–3 min bipolar variations for 1 h when the IMF had a small positive bz-component and a Parker-spiral orientation in the x,y-plane. Brief 33 s intervals with excellent deHoffman Teller frames were observed satisfying the Walén relation. Detailed comparisons with 2-D MHD simulations indicate that Cluster encountered rotational discontinuities generated by Kelvin-Helmholtz instability. We estimate a wave length of 6 RE and a wave vector with a significant z-component.
The presence of large sunspots near the central solar meridian at the times of modern Japanese auroral observations
Authors: Willis D. M. , Henwood R. , Stephenson F. R. 
Published: June 2010

Abstract. The validity of a technique developed by the authors to identify historical occurrences of intense geomagnetic storms, which is based on finding approximately coincident observations of sunspots and aurorae recorded in East Asian histories, is corroborated using more modern sunspot and auroral observations. Scientific observations of aurorae in Japan during the interval 1957–2004 are used to identify geomagnetic storms that are sufficiently intense to produce auroral displays at low geomagnetic latitudes. By examining white-light images of the Sun obtained by the Royal Greenwich Observatory, the Big Bear Solar Observatory, the Debrecen Heliophysical Observatory and the Solar and Heliospheric Observatory spacecraft, it is found that a sunspot large enough to be seen with the unaided eye by an "experienced" observer was located reasonably close to the central solar meridian immediately before all but one of the 30 distinct Japanese auroral events, which represents a 97% success rate. Even an "average" observer would probably have been able to see a sunspot with the unaided eye before 24 of these 30 events, which represents an 80% success rate. This corroboration of the validity of the technique used to identify historical occurences of intense geomagnetic storms is important because early unaided-eye observations of sunspots and aurorae provide the only possible means of identifying individual historical geomagnetic storms during the greater part of the past two millennia.
Substorm topology in the ionosphere and magnetosphere during a flux rope event in the magnetotail
Authors: Amm O. , Nakamura R. , Frey H. U. , Ogawa Y. , Kubyshkina M. , Balogh A. , Rème H. 
Published: June 2010

Abstract. On 13 August 2002, at ~23:00 UT, about 10 min after a substorm intensification, Cluster observes a flux rope in the central magnetotail, followed by a localised fast flow event about oneminute later. Associated with the flux rope event, a traveling compression region (TCR) is seen by those Cluster spacecraft which reside in the lobe. In the conjugate ionospheric region in Northern Scandinavia, the MIRACLE network observes the ionospheric equivalent currents, and the electron densities and electric fields are measured by the EISCAT radar along a meridional scanning profile. Further, the auroral evolution is observed with the Wideband Imaging Camera (WIC) on the IMAGE satellite. We compare in detail the substorm evolution as observed in the ionosphere and in the magnetosphere, and examine whether topological correspondences to the flux rope event exist in the ionospheric signatures. The large-scale mapping of both the location and the direction of the flux rope to the ionosphere shows an excellent correspondence to a lens-shaped region of an auroral emission minimum. This region is bracketed by an auroral region equatorward of it which was preexisting to the substorm intensification, and a substorm-related auroral region poleward of it. It is characterised by reduced ionospheric conductances with respect to its environment, and downward field-aligned current (FAC) observed both in the magnetosphere and in the ionosphere. As determined from the ionospheric data, this downward FAC area is moving eastward with a speed of ~2 km s-1, in good agreement with the mapped plasma bulk velocity measured at the Cluster satellite closest to that area. Further southwestward to this leading downward FAC area, a trailing upward FAC area is observed that moves eastward with the same speed. The direction of the ionospheric electric field permits a current closure between these two FAC areas through the ionosphere. We speculate that these FAC areas may correspond to the ends of the flux rope in its symmetry direction.
Lidar observations of middle atmospheric gravity wave activity over a low-latitude site (Gadanki, 13.5° N, 79.2° E)
Authors: Sivakumar V. , Rao P. B. , Bencherif H. 
Published: June 2010

Abstract. The low-latitude middle atmospheric gravity wave characteristics are presented using 310 nights of Rayleigh lidar observations made at Gadanki (13.5° N, 79.2° E) over the period from March 1998 to December 2002. The gravity wave characteristics are presented in terms of vertical wave number and frequency spectra, along with the estimated potential energy for the four seasons, namely, spring, summer, autumn and winter. The computed wave number spectra for both the stratosphere and the mesosphere are found to differ significantly from a saturated model predicted spectrum. The spectra were found to be shallower at lower wave numbers and steeper at higher wave numbers with transition at ~8.85×10-4 cy/m. The computed frequency spectra seem to follow the model plot with a power law index of -5/3 above a frequency of ~2×10-4 Hz. The estimated potential energy per unit mass increases gradually up to ~60 km and then rather rapidly above this height to reach values of the order of 200J/kg at ~70 km.
Precipitation and total power consumption in the ionosphere: Global MHD simulation results compared with Polar and SNOE observations
Authors: Palmroth M. , Janhunen P. , Germany G. , Lummerzheim D. , Liou K. , Baker D. N. , Barth C. , Weatherwax A. T. , Watermann J. 
Published: June 2010

Abstract. We compare the ionospheric electron precipitation morphology and power from a global MHD simulation (GUMICS-4) with direct measurements of auroral energy flux during a pair of substorms on 28-29 March 1998. The electron precipitation power is computed directly from global images of auroral light observed by the Polar satellite ultraviolet imager (UVI). Independent of the Polar UVI measurements, the electron precipitation energy is determined from SNOE satellite observations on the thermospheric nitric oxide (NO) density. We find that the GUMICS-4 simulation reproduces the spatial variation of the global aurora rather reliably in the sense that the onset of the substorm is shown in GUMICS-4 simulation as enhanced precipitation in the right location at the right time. The total integrated precipitation power in the GUMICS-4 simulation is in quantitative agreement with the observations during quiet times, i.e., before the two substorm intensifications. We find that during active times the GUMICS-4 integrated precipitation is a factor of 5 lower than the observations indicate. However, we also find factor of 2-3 differences in the precipitation power among the three different UVI processing methods tested here. The findings of this paper are used to complete an earlier objective, in which the total ionospheric power deposition in the simulation is forecasted from a mathematical expression, which is a function of solar wind density, velocity and magnetic field. We find that during this event, the correlation coefficient between the outcome of the forecasting expression and the simulation results is 0.83. During the event, the simulation result on the total ionospheric power deposition agrees with observations (correlation coefficient 0.8) and the AE index (0.85).
Radionuclides: Anthropogenic
Authors: Mietelski Jerzy W. 
Published: June 2010

AbstractFollowing the definition of anthropogenic radioactivity, the main discoveries in this field made in the 1930s are briefly presented. The main facts about radioisotopes classification, radioactive decay, and artificial radionuclide production are then described. The article then provides a general overview on anthropogenic sources of radioactivity such as nuclear explosions, nuclear accidents, routine releases from nuclear reactors, releases due to nuclear weapon production programs or nuclear fuel reprocessing installations, and nuclear medicine. A description of modern techniques applied in determining radioactivity in the environment as well as a very general introduction to the concept of radioecology and some basic information on environmental remediation are presented.
Radium: Radionuclides
Authors: Vandenhove Hildegarde , Verrezen Freddy , Landa Edward R. 
Published: June 2010

AbstractThis article describes (1) the occurrence, chemistry, and bioavailability of radium (Ra) in terrestrial and aquatic environments, and its analysis in environmental samples, (2) the nature of naturally occurring radioactive materials (NORM) and their role in radium‐contamination scenarios, and (3) the geochemical processes and remedial measures associated with radium‐contaminated water and soil. Radium is the heaviest of the Group II, alkaline earth metals. Radium is exclusively divalent and its chemistry resembles that of barium. Radium has a limited environmental mobility due to sorption (e.g., by hydrous oxides of Fe, Mn, and Al) and coprecipitation reactions (e.g., with barite).All isotopes of radium (atomic number 88) are radioactive. The most important radium isotopes are226Ra (half life 1600 years) and228Ra (half life 5.7 years), decay products of, respectively, the238U and the232Th series. As members of natural radioactive decay series, these radium isotopes are found in uranium‐ and thorium‐bearing minerals. Concentrations of uranium and thorium in rocks can range from those of ore‐grade deposits to the trace levels typical of common rock‐forming minerals.In uncontaminated surface waters, radium content is generally low and within a narrow range (0.5–20 mBq l−1). Radium in groundwater is highly variable (<0.52–55 000 mBq l−1) and can arise from natural sources, resulting from the interaction of groundwater with radium‐bearing materials or indirectly from man's exploitation of the radioactive minerals of uranium and thorium. The major challenge associated with many NORM‐containing residues or NORM‐contaminated sites is the larger volumes of material and the relatively low specific activities.
Sulfur: Radionuclides
Authors: Tsay Olga G. , Churchill David G. 
Published: June 2010

Abstract35S is a radionuclide with a half‐life of 87.5 days and it decays via β‐emission. It is available from natural and anthropogenic sources. It is cosmogenic, that is, it is produced by the collision of atmospheric argon with cosmic rays. Anthropogenic molecular sources of35S include carbonyl sulfide (CO35S) and hydrogen sulfide (H235S), which are released from nuclear reactors. The impact of the incorporation of these compounds into plants and animals is of particular interest and concern with regard to the accumulation of35S in human food. Radioisotopes of sulfur can be detected by a Geiger–Müller counter and liquid scintillation counting techniques.
Indium: Radionuclides
Authors: Wehmschulte Rudolf J. 
Published: June 2010

Abstract

Although the major isotope
115
indium (95.7% abundance) is a β‐emitter, it has a very long half‐life at 6 × 10
14
(600 trillion) years and hence can be considered practically nonradioactive. Other radioactive indium isotopes are short‐lived and are either part of the decay processes of other radioactive nuclei or are prepared artificially for medicinal and analytical purposes in very small amounts. The environmental impact of radioactive indium isotopes is very minor and standard safety procedures for low‐level wastes are sufficient.
Thallium: Radionuclides
Authors: Wehmschulte Rudolf J. 
Published: June 2010

AbstractOf the 35 radioactive isotopes, only201Tl and204Tl with half‐lives of 73 h and 3.78 y are applied in medicine and materials analysis. Both are usually generated in situ on site in small amounts just prior to use in cyclotrons. Owing to the small amounts applied and generated, they are of minor concern as environmental radionuclides despite their high mobility under physiological and environmental conditions.
Iodine: Radionuclides
Authors: Hu Qinhong , Moran Jean E. 
Published: June 2010

AbstractThis article provides a review of iodine with regard to the basic chemistry, occurrence, speciation, separation, analysis, fate, and transport. Biogeochemical cycling of iodine in the environment is complex because iodine occurs in multiple oxidation states (ranging from −1 to +7), and inorganic and organic species may be hydrophilic, atmophilic, and biophilic. Organically bound iodine can be a significant fraction of total iodine in the atmosphere, biosphere, hydrosphere, and lithosphere. Nuclear‐fuel reprocessing facilities constitute the major source (>90%) of129I released to the environment. It has been recognized that129I is a very important dose contributor in risk assessment because of its tendency to concentrate in the human thyroid gland, long half‐life, and presumably high mobility. Speciation, input concentration, and residence time effects will influence the biogeochemical cycling of anthropogenic129I deposited on surface soils.
Cobalt: Radionuclides
Authors: Lima Enrique 
Published: June 2010

AbstractRadionulcides of cobalt are generated through nuclear reactions from other stables isotopes. The most common radionuclide of cobalt is60Co, which is generated in nuclear power plants. Medical equipment is also a minor source of radioactive cobalt. Important applications of60Co in the field of medicine, biology, and food are possible because of the powerful emitted γ‐rays (1.17 and 1.33 MeV). However, this kind of radiation may be very dangerous to human beings; serious cellular damage can occur if exposed directly to doses as high as 1000 rad. Thus, discharges of radioactive cobalt to the environment should be minimized, but accidental releases have occurred. The chemical behavior of cobalt in aqueous media is a determinant for the stabilization of cobalt in polluted effluents. Water and soil in several regions in the world are contaminated. The chemical complexity of seawater and soil makes it difficult to remediate60Co. The chemical media determine the stabilization and rate of transport through marine media and soil. Several strategies have been designed to remediate water and soil polluted with cobalt radionuclides. This article describes some of the common uses of cobalt as well as some problems associated with cobalt radionuclides.
Technetium: Radionuclides
Authors: Hu Qinhong 
Published: June 2010

AbstractThis article provides a review of Tc with regards to the basic chemistry, occurrence, speciation, separation, analysis, fate, and transport. Environmental99Tc originates from the nuclear fuel cycle, with most of the isotope (>90%) discharged from reprocessing plants in Europe. It has been recognized that99Tc is a very important dose contributor in risk assessment, because of its high abundance, long half‐lives, and presumably high mobility. Essentially all the technetium on the Earth has been created by human activities involving fissionable materials. Among 11 metastates of technetium,97mTc is the most stable, with a half‐life of 90.1 days. The common oxidation states of technetium include 0, +2, +4, +5, +6, and +7. Depending upon the redox conditions, Tc primarily exists in two (+7 and +4) stable oxidation states in the subsurface. Under oxidizing conditions, technetium (VII) will exist as the mobile pertechnetate ion (TcO4−) in aqueous solution. Reduction of TcO4−to Tc(IV) species (TcO2 · nH2O) will decrease Tc mobility, because Tc(IV) species are strongly retarded from mineral sorption and/or precipitation. ICP‐MS is the common analytical method used to quantify Tc levels.
Rhenium: Radionuclides
Authors: Tagami Keiko , Uchida Shigeo 
Published: June 2010

AbstractThe occurrence, chemistry, and speciation of rhenium (Re) in environmental components such as soil and water, as well as rhenium separation and analytical characterization techniques in the environment, are summarized. Rhenium has two isotopes: one is stable185Re and the other is radioactive187Re, which has a very long half‐life of 4.35 × 1010years. The decay system,187Re–187Os has been used for dating rocks and meteorites. Artificially made radioisotopes with short half‐lives, such as186Re and188Re have been used in radiopharmaceuticals. Because of similarities in chemistry, rhenium has been used as a chemical analog of technetium.
Neptunium: Radionuclides
Authors: Runde Wolfgang , Goff George S. 
Published: June 2010

AbstractFollowing the element uranium, neptunium is the fourth element in the actinide series. Although primordial neptunium isotopes formed during the creation of the solar system billions of years ago have long since decayed away, neptunium continues to be formed by the nuclear reactions in naturally occurring uranium deposits. Currently, trace amounts of neptunium isotopes can be isolated from uranium ore minerals. Most of present‐day inventory of neptunium originates from human activities, such as nuclear weapons testing, nuclear accidents, or irradiation of uranium fuel for producing nuclear energy. All neptunium isotopes are highly radioactive and pose extreme health hazards to humans when ingested or inhaled. Neptunium exhibits five oxidation states (III–VII) in solution and solid state, but only the IV and V oxidation states are relevant under most environmental conditions. In the +IV state, neptunium is insoluble and forms stable complexes with ligands abundant in natural environments (such as hydroxide, carbonate, or humic substances), and can adsorb onto mobile colloidal matter. In contrast, neptunium(V) forms a soluble dioxo‐cation in solution (NpO$_{2}^{+}$), which exhibits an increased solubility, weaker complex formation, and higher stability in the aqueous phases of aquatic systems. Thus, neptunium(V) is mostly characterized as the dominant solution species, while Np(IV) is found to be adsorbed on sediments, minerals, and colloidal particles. There is no large‐scale use of neptunium in industrial applications.