bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rocket and radar investigation of background electrodynamics and bottom-type scattering layers at the onset of equatorial spread &lt;i&gt;F&lt;/i&gt;
Authors: Hysell D. L. , Larsen M. F. , Swenson C. M. , Barjatya A. , Wheeler T. F. , Bullett T. W. , Sarango M. F. , Woodman R. F. , Chau J. L. , Sponseller D. 
Published: June 2010

Abstract. Sounding rocket experiments were conducted during the NASA EQUIS II campaign on Kwajalein Atoll designed to elucidate the electrodynamics and layer structure of the postsunset equatorial F region ionosphere prior to the onset of equatorial spread F (ESF). Experiments took place on 7 and 15 August 2004, each comprised of the launch of an instrumented and two chemical release sounding rockets. The instrumented rockets measured plasma number density, vector electric fields, and other parameters to an apogee of about 450 km. The chemical release rockets deployed trails of trimethyl aluminum (TMA) which yielded wind profile measurements. The Altair radar was used to monitor coherent and incoherent scatter in UHF and VHF bands. Electron density profiles were also measured with rocket beacons and an ionosonde. Strong plasma shear flow was evident in both experiments. Bottom-type scattering layers were observed mainly in the valley region, below the shear nodes, in westward-drifting plasma strata. The layers were likely produced by wind-driven interchange instabilities as proposed by Kudeki and Bhattacharyya (1999). In both experiments, the layers were patchy and distributed periodically in space. Their horizontal structure was similar to that of the large-scale plasma depletions that formed later at higher altitude during ESF conditions. We argue that the bottom-type layers were modulated by the same large-scale waves that seeded the ESF. A scenario where the large-scale waves were themselves produced by collisional shear instabilities is described.
Observations of high-velocity SAPS-like flows with the King Salmon SuperDARN radar
Authors: Koustov A. V. , Drayton R. A. , Makarevich R. A. , McWilliams K. A. , St-Maurice J.-P. , Kikuchi T. , Frey H. U. 
Published: June 2010

Abstract. In this study, a focused investigation of the potential for the King Salmon (KS) SuperDARN HF radar to monitor high-velocity flows near the equatorial edge of the auroral oval is undertaken. Events are presented with line-of-sight velocities as high as 2km/s, observed roughly along the L-shell. Statistically, the enhanced flows are shown to be typical for the dusk sector (16:00–23:00 MLT), and the average velocity in this sector is larger (smaller) for winter (summer) conditions. It is also demonstrated that the high-velocity flows can be very dynamical with more localized enhancements existing for just several minutes. These short-lived enhancements occur when the luminosity at the equatorial edge of the auroral oval suddenly decreases during the substorm recovery phase. The short-lived velocity enhancements can be established because of proton and ion injections into the inner magnetosphere and low conductance of the ionosphere and not because of enhanced tail reconnection. This implies that some KS velocity enhancements have the same origin as subauroral polarization streams (SAPS).
Saturn's aurora in the January 2004 events
Authors: Belenkaya E. S. , Cowley S. W. H. , Alexeev I. I. 
Published: June 2010

Abstract. Differences in the solar wind interaction with the magnetosphere of Saturn relative to the Earth result from the decrease in the solar wind plasma density and magnetic field strength with distance from the Sun, and from the change in the average angle of the IMF at Saturn's orbit. Other reasons are related to Saturn's rapid rotation and internal magnetospheric plasma sources. Moreover, the IMF structure observed by Cassini in 2003–2004 during the approach to Saturn is consistent with corotating interaction regions (CIRs) existing during the declining phase of the solar cycle. Two cases on 16 and 26 January 2004 are considered when disturbances in the solar wind passed Cassini and then Saturn. After the solar wind shock encountered the kronian magnetosphere, the auroral oval became brighter (especially at dawn) with a reduced radius. In these cases the auroral power was anti-correlated with the radius of the oval. Possible mechanisms responsible for such unexpected behavior are presented and discussed in detail.
Sunset transition of negative charge in the D-region ionosphere during high-ionization conditions
Authors: Verronen P. T. , Ulich Th. , Turunen E. , Rodger C. J. 
Published: June 2010

Abstract. The solar proton event of October 1989 and especially the sunset of 23 October is examined in this study of negative ion chemistry, which combines measurements of nitric oxide, electron density, and cosmic radio noise absorption with ion and neutral chemistry modelling. Model results show that the negative charge transition from electrons to negative ions during sunset occurs at altitudes below 80 km and is dependent on both ultraviolet and visible solar radiation. The ultraviolet effect is mostly due to rapid changes in atomic oxygen and O2(1Δg), while the decrease in NO3- photodetachment plays a minor role. The effect driven by visible wavelengths is due to changes in photodissociation of CO3- and the subsequent electron photodetachment from O-, and at higher altitudes is also due to a decrease in the photodetachment of O2-. The relative sizes of the ultraviolet and visible effects vary with altitude, with the visible effects increasing in importance at higher altitudes, and they are also controlled by the nitric oxide concentration. These modelling results are in good agreement with EISCAT incoherent scatter radar and Kilpisjärvi riometer measurements.
Longitudinal drift of substorm electrons as the reason of impulsive precipitation events and VLF emissions
Authors: Lubchich A. A. , Yahnin A. G. , Titova E. E. , Demekhov A. G. , Trakhtengerts V. Yu. , Manninen J. , Turunen T. 
Published: June 2010

Abstract. Using the data from satellite CRRES and three geostationary LANL spacecraft, the propagation of an electron cloud from midnight to the evening sector is investigated. An electron cloud was injected during a weak isolated substorm that developed on a quiet geomagnetic background. It is found that within the local time sector from 03:00 until at least 08:00 MLT, the propagation of electrons at perpendicular pitch-angles is well described by a simple model of drift in the dipole magnetic field. The flux levels in the field-aligned electrons increase simultaneously with the flux at perpendicular pitch angles, which is attributed to the pitch angle diffusion by the whistler mode. This pitch-angle diffusion leads to precipitation of electrons from a drifting cloud and an increase in the ionospheric electron density, simultaneously observed above Tromsø, Norway, by the EISCAT UHF radar in the morning sector (04:40–05:25 MLT). The precipitation develops as quasi-periodic pulses with a period of about 100 s. We discuss the models of pulsating precipitation due to the whistler cyclotron instability and show that our observations can be explained by such a model.
Change in ozone depletion rates beginning in the mid 1990s: trend analyses of the TOMS/ SBUV merged total ozone data, 1978-2003
Authors: Krzyscin J. W. 
Published: June 2010

Abstract. Statistical analyses have been applied to the gridded monthly means of total ozone from combined TOMS and SBUV measurements (version 8 of the data) for the period 1978-2003. We focus on the detection of a change in the trend pattern by searching for a turnaround in the previous downward trend. The ozone time series have been examined separately for each grid point and season, taking into account the various descriptions of the trend term: double-linear, proportional to the index of the overall chlorine content in the stratosphere, and a smooth curve without an a priori defined shape (the output of the regression model). Standard explanatory variables representing physical and chemical processes known to influence the ozone distribution have been considered: Mg II index, QBO wind at 10 and 30 hPa, zonal wind anomalies at 50 hPa along the 60° north or 60° south circle, the index of the stratospheric aerosols loading in the NH or SH, and the tropopause pressure. The multivariate adaptive regression splines methodology is used to find an optimal set of the explanatory variables and shape of the trend curve. The statistical errors of the models' estimates have been calculated using block bootstrapping of the models' residuals. The results appear to be consistent among models using different formulations of the trend pattern. The 2003 level of total ozone after the removal of the variations due to the parameterized dynamical/chemical forcing on the ozone is still below the long-term (1978-2003) mean level over the extratropical regions. The deficit is ~2-5% in the NH and much larger in the SH and exhibits clear seasonal variability, ~15% in autumn, ~10% in winter, and ~-5% in spring and summer. The present total ozone level is higher beyond the tropics than that in the mid 1990s but it is too early to announce a beginning of the ozone recovery there because of the trend uncertainties, due to errors of the regression estimates for individual grid points and longitudinal variability of the trend pattern. A rigorous statistical test has shown the statistically significant turnaround for some grid points over the extratropical region and a deepening of the ozone negative trend has not been found for any grid point.
Observations of concentrated generator regions in the nightside magnetosphere by Cluster/FAST conjunctions
Authors: Hamrin M. , Marghitu O. , Rönnmark K. , Klecker B. , André M. , Buchert S. , Kistler L. M. , McFadden J. , Rème H. , Vaivads A. 
Published: June 2010

Abstract. Here and in the companion paper, Marghitu et al. (2006), we investigate plausible auroral generator regions in the nightside auroral magnetosphere. In this article we use magnetically conjugate data from the Cluster and the FAST satellites during a 3.5-h long event from 19-20 September 2001. Cluster is in the Southern Hemisphere close to apogee, where it probes the plasma sheet and lobe at an altitude of about 18 RE. FAST is below the acceleration region at approximately 0.6 RE. Searching for clear signatures of negative power densities, E·J<0, in the Cluster data we can identify three concentrated generator regions (CGRs) during our event. From the magnetically conjugate FAST data we see that the observed generator regions in the Cluster data correlate with auroral precipitation. The downward Poynting flux observed by Cluster, as well as the scale size of the CGRs, are consistent with the electron energy flux and the size of the inverted-V regions observed by FAST. To our knowledge, these are the first in-situ observations of the crossing of an auroral generator region. The main contribution to E·J<0 comes from the GSE EyJy. The electric field Ey is weakly negative during most of our entire event and we conclude that the CGRs occur when the duskward current Jy grows large and positive. We find that our observations are consistent with a local southward expansion of the plasma sheet and/or rather complicated, 3-D wavy structures propagating over the Cluster satellites. We find that the plasma is working against the magnetic field, and that kinetic energy is being converted into electromagnetic energy. Some of the energy is transported away as Poynting flux.
IMF effect on sporadic-E layers at two northern polar cap sites: Part II – Electric field
Authors: Nygrén T. , Aikio A. T. , Voiculescu M. , Ruohoniemi J. M. 
Published: June 2010

Abstract. This paper is the second in a series on a study of the link between IMF and sporadic-E layers within the polar cap. In Paper I (Voiculescu et al., 2006), an analysis of the sporadic-E data from Thule and Longyearbyen was presented. Here we concentrate on the electric field mechanism of sporadic-E generation. By means of model calculations we show that the mechanism is effective even at Thule, where the direction of the geomagnetic field departs from vertical only by 4. The model calculations also lead to a revision of the electric field theory. Previously, a thin layer was assumed to grow at a convergent null in the vertical ion velocity, which is formed when the electric field points in the NW sector. Our calculations indicate that in the dynamic process of vertical plasma compression, a layer is generated at altitudes of high vertical convergence rather than at a null. Consequently, the layer generation is less sensitive than previously assumed to fluctuations of the electric field direction within the NW sector. The observed diurnal variations of sporadic-E occurrence at Longyearbyen and Thule are compared with the diurnal variations of the electric field, calculated using a representative range of IMF values by means of the statistical APL model. The results indicate that the main features of Es occurrence can be explained by the convection pattern controlled by the IMF. Electric fields calculated from the IMF observations are also used for producing distributions of sporadic-E occurrence as a function of electric field direction at the two sites. A marked difference between the distributions at Thule and Longyearbyen is found. A model estimate of the occurrence probability as a function of electric field direction is developed and a reasonable agreement between the model and the experimental occurrence is found. The calculation explains the differences between the distributions at the two sites in terms of the polar cap convection pattern. The conclusion is that the electric field is the major cause for sporadic-E generation and, consequently, IMF has a clear control on the occurrence of sporadic E within the polar cap.
Radionuclides: Natural
Authors: Larivière Dominic , Guérin Nicolas 
Published: June 2010

AbstractThe natural ionizing radiation present on our planet comes from many sources and generates most of the radioactivity that surrounds us. Primordial radionuclides, defined as radionuclides present since the formation of Earth about 4.6 × 109years ago, play a critical role in our understanding of geological conditions on our planet over its whole history. Radioactivity initiated by the successive decay of232Th,235U, and238U is essentially responsible for the presence of radioisotopes of lead, polonium, bismuth, astatine, radon, francium, radium, and protactinium on Earth. Because of their short half‐lives with respect to Earth's geologic timescale, the decay of these radionuclides is responsible for a significant portion of the doses of natural radioactivity received by humans. Cosmic radiation, originating from both within and beyond our solar system, completes the list of significant modes of production of natural radioactivity in the atmosphere and the lithosphere. Minor sources of natural radioactivity (including radionuclides produced by cosmic neutron bombardments and spontaneous fission in uranium and thorium minerals) are known to generate quantities of transuranium isotopes and fission products, which are generally associated with the development of nuclear power.
Speciation: Radionuclides
Authors: Salbu Brit 
Published: June 2010

AbstractTo assess the environmental impact of radioactive contamination of different ecosystems, information on source terms, mobility, biological uptake, and associated effects is needed. However, naturally occurring and artificially produced radionuclides can be present in different physicochemical forms (ions, colloids, nanoparticles, pseudocolloids, particles) influencing the mobility and biological uptake. Following severe nuclear events associated with the nuclear weapon or fuel cycles, a major fraction of refractory radionuclides will be present as radioactive particles; radionuclides are also present as colloids or low molecular mass (LMM) ionic species in effluents from nuclear installations. Thus, the distribution of radionuclide species depends on the source and release scenarios. LMM radionuclide species are believed to be mobile and potentially bioavailable, while high molecular mass (HMM) species such as nanoparticles, colloids, polymers, and pseudocolloids are mobile in water. Radioactive particles are considered biologically inert, but can be retained in filtering organisms as well as in soils and sediments. If mobile species are present, ecosystem transfer is relatively fast, whereas the ecosystem transfer is delayed if particles are present. Owing to time‐dependent transformation processes such as interactions of mobile and reactive radionuclide species with components in soils and sediments or particle weathering and subsequent remobilization of associated radionuclide species, the original distribution of radionuclides deposited in ecosystems will change over time. Therefore, information on radionuclide species released and deposited, as well as on time‐dependent transformation processes influencing the distribution of radionuclide species, is essential for the assessment of the environmental impact and risk associated with radionuclide contamination. This article summarizes available speciation techniques that should be utilized within radioecology, including fractionation and solid‐state speciation, to characterize radionuclide species in waters, soils, and sediments.
Tritium: Radionuclide
Authors: Galeriu Dan , Melintescu Anca 
Published: June 2010

AbstractTritium is the heavy isotope of hydrogen and can therefore participate directly in a wide range of biological functions. It is formed through natural processes but is also generated through human activity in nuclear reactors, fusion, and weapons. In addition, it has some commercial applications. Its occurrence, chemical and physical properties, and speciation are unique in comparison to other radionuclides. This article summarizes what is currently known about tritium with regard to the isotope's occurrence, chemistry, speciation, remediation, separation, and the analytical techniques used for its detection and quantification. The potential impact of tritium on human health is also described.
Strontium: Radionuclides
Authors: Guillén Francisco Javier , Baeza Antonio , Salas Alejandro 
Published: June 2010

AbstractStrontium has several radioactive isotopes, with90Sr being the most important in the environment. This radionuclide dispersed worldwide as a consequence of the atmospheric nuclear weapon tests in the 1960s, and is locally enhanced owing to the accidents involving radioactive material.90Sr is a pure β‐emitter and it may be detected by several detection techniques (gas‐flow proportional, liquid scintillation, Cerenkov counting, and ICP‐MS), after an appropriate radiochemical separation. The environmental behavior of radiostrontium is governed by its chemical similarities to calcium. It is usually associated with the mobile and bioavailable fractions in soils, and with the low MW fraction in aquatic ecosystems. The potential human exposure to radiostrontium is mainly due to the ingestion of food, milk and cereals being the two major sources. This exposure can be reduced to some extent by the addition of calcium fertilizers to minimize the soil‐to‐plant transfer of radiostrontium, and by increasing cattle calcium intake to decrease the90Sr content in milk.
Lead: Radionuclides
Authors: Sabuti Asnor Azrin , Rahim Mohamed Che Abd 
Published: June 2010

AbstractLead (Pb) is a highly toxic and radiogenic metal. It occurs naturally in the Earth, but is not very abundant. Even so, lead isotopes have been very useful ss tracers in glaciology, limnology, oceanography, and in atmospheric studies of global (transboundary) and local pollution. The dominant radioisotope of lead is210Pb, a very ubiquitous secondary radionuclide that is formed from238U decay via222Rn.210Pb originates from the Earth's crust, through the decay of226Ra. There are many factors that complicate the behavior of210Pb in soil, air, and water. Owing to these, a great deal of effort has been devoted to the quantitative determination of lead isotopes over the past few years. The separation and counting techniques for lead need to be rapid, convenient, and precise, and utilize very small amounts of material. Humans are exposed to lead through ingestion and inhalation, and it is stored for long periods of time mainly in bone and teeth. Thus, more studies on environmental exposures to lead need to be conducted, particularly for air monitoring, dust, water, and soil sampling, and lead‐based product sampling.
Polonium: Radionuclides
Authors: Alam Lubna , Rahim Mohamed Che Abd 
Published: June 2010

Abstract

All polonium isotopes are radioactive with only three having appreciable half‐lives:
208
Po,
209
Po, and
210
Po. It is a highly toxic element and is a health hazard if taken into the body. Polonium is a naturally occurring radionuclide and is present in the environment and in people at very low concentrations. Polonium concentrations in the environment can vary by orders of magnitude.
210
Po concentration in soil varies according to soil strata, depth, sedimentation and biological processes, fertilization and pH. Incomplete burning of fuels of coal loading plays an important role in the concentration of
210
Po in air. Usually, the activity concentration of
210
Po in surface air is low. Polonium can be separated by irradiating stable bismuth‐209 with thermal neutrons resulting in the formation of radioactive
210
Bi, which decays into
210
Po.
Xenon: Radionuclides
Authors: Saey Paul R.J. 
Published: June 2010

AbstractRadioxenon isotopes are noble gases mainly produced in nuclear fission e.g., uranium‐235. In nuclear medicine, xenon‐133 isotopes are used for measuring the physiological parameters of lung ventilation and to image the lungs. They are further used in isotonic solutions to image blood flow, particularly cerebral blood flow. Most radioactive isotopes of this element are produced by a nuclear fission reaction of uranium‐235, uranium‐238, or plutonium‐239. Xenon‐133 is the most abundant radioxenons observed in environmental samples, although contributions of131mXe and135Xe can be determined down to a few percent of the total β‐activity. The minimum detectable concentration (MDC) for133Xe in routine samples is about 1 mBq m−3. This article will describe the production, applications, occurrence, and measurement of the various xenon isotopes.
Radon: Radionuclides
Authors: Tracy Bliss L. 
Published: June 2010

AbstractRadon is a naturally occurring radioactive gas formed by the decay of uranium and thorium in the Earth's crust. At atomic number 86, it is the heaviest member of the noble or inert gas family, which also includes helium, neon, argon, krypton, and xenon. Unlike the other members of the family, radon has no stable isotopes. Of the 34 known radioactive isotopes of radon, only three are supported by the decay of primordial radionuclides, and only two occur with any significant abundance in nature. The three isotopes, along with their half‐lives, are222Rn (3.8235 days),220Rn (55.6 s), and219Rn (3.96 s). Both222Rn and220Rn decay by the emission of α‐particles and give rise to a number of short‐lived progeny.222Rn and220Rn are the only ones regarded as having any health impacts and this is due to their short‐lived progeny—218Po,214Pb,214Bi, and214Po from222Rn;216Po,212Pb,212Bi,212Po, and208Tl from220Rn. Being a gas, radon diffuses readily into the atmosphere and may build up to hazardous concentrations in confined spaces in homes and underground mines. Radon is the largest single contributor to natural background radiation exposure worldwide. Radon is now recognized as the second leading cause of lung cancer, following tobacco smoking, and is responsible for up to 20 000 deaths per year in the United States and 1900 deaths per year in Canada. Many countries have now established programs to reduce radon exposures to the population.