bluuebunny/crossref_metadata_2025_split huggingface dataset:
Local structure of the magnetotail current sheet: 2001 Cluster observations
Authors: Runov A. , Sergeev V. A. , Nakamura R. , Baumjohann W. , Apatenkov S. , Asano Y. , Takada T. , Volwerk M. , Vörös Z. , Zhang T. L. , Sauvaud J.-A. , Rème H. , Balogh A. 
Published: June 2010

Abstract. Thirty rapid crossings of the magnetotail current sheet by the Cluster spacecraft during July-October 2001 at a geocentric distance of 19 RE are examined in detail to address the structure of the current sheet. We use four-point magnetic field measurements to estimate electric current density; the current sheet spatial scale is estimated by integration of the translation velocity calculated from the magnetic field temporal and spatial derivatives. The local normal-related coordinate system for each case is defined by the combining Minimum Variance Analysis (MVA) and the curlometer technique. Numerical parameters characterizing the plasma sheet conditions for these crossings are provided to facilitate future comparisons with theoretical models. Three types of current sheet distributions are distinguished: center-peaked (type I), bifurcated (type II) and asymmetric (type III) sheets. Comparison to plasma parameter distributions show that practically all cases display non-Harris-type behavior, i.e. interior current peaks are embedded into a thicker plasma sheet. The asymmetric sheets with an off-equatorial current density peak most likely have a transient nature. The ion contribution to the electric current rarely agrees with the current computed using the curlometer technique, indicating that either the electron contribution to the current is strong and variable, or the current density is spatially or temporally structured.
Gravity waves observed from the Equatorial Wave Studies (EWS) campaign during 1999 and 2000 and their role in the generation of stratospheric semiannual oscillations
Authors: Deepa V. , Ramkumar G. , Krishna Murthy B. V. 
Published: June 2010

Abstract. The altitude profiles of temperature fluctuations in the stratosphere and mesosphere observed with the Rayleigh Lidar at Gadanki (13.5° N, 79.2° E) on 30 nights during January to March 1999 and 21 nights during February to April 2000 were analysed to bring out the temporal and vertical propagation characteristics of gravity wave perturbations. The gravity wave perturbations showed periodicities in the 0.5–3-h range and attained large amplitudes (4–5 K) in the mesosphere. The phase propagation characteristics of gravity waves with different periods showed upward wave propagation with a vertical wavelength of 5–7 km. The mean flow acceleration computed from the divergence of momentum flux of gravity waves is compared with that calculated from monthly values of zonal wind obtained from RH-200 rockets flights. Thus, the contribution of gravity waves towards the generation of Stratospheric Semi Annual Oscillation (SSAO) is estimated.
A numerical study of cell merger over Cuba – Part I: implementation of the ARPS/MM5 models
Authors: Pozo D. , Borrajero I. , Marín J. C. , Raga G. B. 
Published: June 2010

Abstract. On 21 July 2001 a number of severe storms developed over the region of Camaguey, Cuba, which were observed by radar. A numerical simulation was performed in order to realistically reproduce the development of the storms observed that day. The mesoscale model MM5 was used to determine the initial, boundary and update conditions for the storm-scale simulation with the model ARPS. Changes to the source code of ARPS were made in order to assimilate the output from the MM5 as input data and a new land-use file with a 1-km horizontal resolution for the Cuban territory was created. A case representing the merger between cells at different stages of development was correctly reproduced by the simulation and is in good agreement with radar observations. The state of development of each cell, the time when the merger occurred, starting from the formation of clouds, the propagation motion of the cells and the increase in precipitation, due to the growth of the area after the merger, were correctly reproduced. Simulated clouds matched the main characteristics of the observed radar echoes, though in some cases, reflectivity tops and horizontal areas were overestimated. Maximum reflectivity values and the heights where these maximum values were located were in good agreement with radar data, particularly when the model reflectivity was calculated without including the snow. The MM5/ARPS configuration introduced in this study, improved sensibly the ability to simulate convective systems, thereby enhancing the local forecasting of convection in the region.
Infrasound - the cause of strong Polar Mesosphere Winter Echoes?
Authors: Kirkwood S. , Chilson P. , Belova E. , Dalin P. , Häggström I. , Rietveld M. , Singer W. 
Published: June 2010

Abstract. The ESRAD 52-MHz and the EISCAT 224-MHz radars in northern Scandinavia observed thin layers of strongly enhanced radar echoes from the mesosphere (Polar Mesosphere Winter Echoes - PMWE) during a solar proton event in November 2004. Using the interferometric capabilities of ESRAD it was found that the scatterers responsible for PMWE show very high horizontal travel speeds, up to 500 ms-1 or more, and high aspect sensitivity, with echo arrival angles spread over as little as 0.3°. ESRAD also detected, on some occasions, discrete scattering regions moving across the field of view with periodicities of a few seconds. The very narrow, vertically directed beam of the more powerful EISCAT radar allowed measurements of the spectral widths of the radar echoes both inside the PMWE and from the background plasma above and below the PMWE. Spectral widths inside the PMWE were found to be indistinguishable from those from the background plasma. We propose that scatter from highly-damped ion-acoustic waves generated by partial reflection of infrasonic waves provides a reasonable explanation of the characteristics of the very strong PMWE reported here.
Substorm onset location and dipole tilt angle
Authors: Wanliss J. 
Published: June 2010

Abstract. From an initial data set of over 200 substorms we have studied a subset of 30 magnetospheric substorms close to magnetic midnight to investigate, in a statistical fashion, the source region of the auroral arc that brightens at the onset of expansive phase. This arc is usually identified as the ionospheric signature of the expansive phase onset that occurs in the magnetotail. All the substorm onsets were identified via ground-based magnetometer and photometer data from the CANOPUS array. Various Tsyganenko global magnetic field models were used to map magnetic field lines from the location of the onset arc out to its greatest radial distance in the magnetotail. The results appear to favour the current disruption model of substorms since the average onset location has an average of 14.1 Earth radii (RE) and is therefore more consistent with theories that place the onset location in the inner magnetotail. For the narrow range of tilts available our modeling indicates the parameter that appears to strongly influence the location of the substorm onset is the dipole tilt angle; as tilt becomes less negative onsets occur further downtail.
Experimental investigation of auroral generator regions with conjugate Cluster and FAST data
Authors: Marghitu O. , Hamrin M. , Klecker B. , Vaivads A. , McFadden J. , Buchert S. , Kistler L. M. , Dandouras I. , André M. , Rème H. 
Published: June 2010

Abstract. Here and in the companion paper, Hamrin et al. (2006), we present experimental evidence for the crossing of auroral generator regions, based on conjugate Cluster and FAST data. To our knowledge, this is the first investigation that concentrates on the evaluation of the power density, E·J, in auroral generator regions, by using in-situ measurements. The Cluster data we discuss were collected within the Plasma Sheet Boundary Layer (PSBL), during a quiet magnetospheric interval, as judged from the geophysical indices, and several minutes before the onset of a small substorm, as indicated by the FAST data. Even at quiet times, the PSBL is an active location: electric fields are associated with plasma motion, caused by the dynamics of the plasma-sheet/lobe interface, while electrical currents are induced by pressure gradients. In the example we show, these ingredients do indeed sustain the conversion of mechanical energy into electromagnetic energy, as proved by the negative power density, E·J<0. The plasma characteristics in the vicinity of the generator regions indicate a complicated 3-D wavy structure of the plasma sheet boundary. Consistent with this structure, we suggest that at least part of the generated electromagnetic energy is carried away by Alfvén waves, to be dissipated in the ionosphere, near the polar cap boundary. Such a scenario is supported by the FAST data, which show energetic electron precipitation conjugated with the generator regions crossed by Cluster. A careful examination of the conjunction timing contributes to the validation of the generator signatures.
Dynamical critical scaling of electric field fluctuations in the greater cusp and magnetotail implied by HF radar observations of F-region Doppler velocity
Authors: Parkinson M. L. 
Published: June 2010

Abstract. Akasofu's solar wind ε parameter describes the coupling of solar wind energy to the magnetosphere and ionosphere. Analysis of fluctuations in ε using model independent scaling techniques including the peaks of probability density functions (PDFs) and generalised structure function (GSF) analysis show the fluctuations were self-affine (mono-fractal, single exponent scaling) over 9 octaves of time scale from ~46 s to ~9.1 h. However, the peak scaling exponent α0 was a function of the fluctuation bin size, so caution is required when comparing the exponents for different data sets sampled in different ways. The same generic scaling techniques revealed the organisation and functional form of concurrent fluctuations in azimuthal magnetospheric electric fields implied by SuperDARN HF radar measurements of line-of-sight Doppler velocity, vLOS, made in the high-latitude austral ionosphere. The PDFs of vLOS fluctuation were calculated for time scales between 1 min and 256 min, and were sorted into noon sector results obtained with the Halley radar, and midnight sector results obtained with the TIGER radar. The PDFs were further sorted according to the orientation of the interplanetary magnetic field, as well as ionospheric regions of high and low Doppler spectral width. High spectral widths tend to occur at higher latitude, mostly on open field lines but also on closed field lines just equatorward of the open-closed boundary, whereas low spectral widths are concentrated on closed field lines deeper inside the magnetosphere. The vLOS fluctuations were most self-affine (i.e. like the solar wind ε parameter) on the high spectral width field lines in the noon sector ionosphere (i.e. the greater cusp), but suggested multi-fractal behaviour on closed field lines in the midnight sector (i.e. the central plasma sheet). Long tails in the PDFs imply that "microbursts" in ionospheric convection occur far more frequently, especially on open field lines, than can be captured using the effective Nyquist frequency and volume resolution of SuperDARN radars.
Coordinated observation of field line resonance in the mid-tail
Authors: Zheng Y. , Lui A. T. Y. , Mann I. R. , Takahashi K. , Watermann J. , Chen S.-H. , Rae I. J. , Mukai T. , Russell C. T. , Balogh A. , Pfaff R. F. , Rème H. 
Published: June 2010

Abstract. Standing Alfvén waves of 1.1 mHz (~15 min in period) were observed by the Cluster satellites in the mid-tail during 06:00-07:00 UT on 8 August 2003. Pulsations with the same frequency were also observed at several ground stations near Cluster's footpoint. The standing wave properties were determined from the electric and magnetic field measurements of Cluster. Data from the ground magnetometers indicated a latitudinal amplitude and phase structure consistent with the driven field line resonance (FLR) at 1.1 mHz. Simultaneously, quasi-periodic oscillations at different frequencies were observed in the post-midnight/early morning sector by GOES 12 (l0≈8.7), Polar (l0≈11-14) and Geotail (l0≈9.8). The 8 August 2003 event yields rare and interesting datasets. It provides, for the first time, coordinated in situ and ground-based observations of a very low frequency FLR in the mid-tail on stretched field lines.
Relation between substorm characteristics and rapid temporal variations of the ground magnetic field
Authors: Viljanen A. , Tanskanen E. I. , Pulkkinen A. 
Published: June 2010

Abstract. Auroral substorms are one of the major causes of large geomagnetically induced currents (GIC) in technological systems. This study deals with different phases of the auroral substorm concerning their severity from the GIC viewpoint. Our database consists of 833 substorms observed by the IMAGE magnetometer network in 1997 (around sunspot minimum) and 1999 (rising phase of the sunspot cycle), divided into two classes according to the Dst index: non-storm (Dst>-40 nT, 696 events) and storm-time ones (Dst<-40 nT, 137 events). The key quantity concerning GIC is the time derivative of the horizontal magnetic field vector (dH/dt) whose largest values during substorms occur most probably at about 5 min after the onset at stations with CGM latitude less than 72 deg. When looking at the median time of the occurrence of the maximum dH/dt after the expansion onset, it increases as a function of latitude from about 15 min at CGM lat=56 deg to about 45 min at CGM lat=75 deg for non-storm substorms. For storm-time events, these times are about 5 min longer. Based on calculated ionospheric equivalent currents, large dH/dt occur mostly during the substorm onset when the amplitude of the westward electrojet increases rapidly.
Flux closure during a substorm observed by Cluster, Double Star, IMAGE FUV, SuperDARN, and Greenland magnetometers
Authors: Milan S. E. , Wild J. A. , Hubert B. , Carr C. M. , Lucek E. A. , Bosqued J. M. , Watermann J. F. , Slavin J. A. 
Published: June 2010

Abstract. We examine magnetic flux closure during an extended substorm interval on 29 August 2004 involving a two-stage onset and subsequent re-intensifications. Cluster and Double Star provide observations of magnetotail dynamics, while the corresponding auroral evolution, convection response, and substorm current wedge development are monitored by IMAGE FUV, SuperDARN, and the Greenland magnetometer chain, respectively. The first stage of onset is associated with the reconnection of closed flux in the plasma sheet; this is accompanied by a short-lived auroral intensification, a modest substorm current wedge magnetic bay, but no significant ionospheric convection enhancement. The second stage follows the progression of reconnection to the open field lines of the lobes; accompanied by prolonged auroral bulge and westward-travelling surge development, enhanced magnetic bays and convection. We find that the tail dynamics are highly influenced by ongoing dayside creation of open flux, leading to flux pile-up in the near-tail and a step-wise down-tail motion of the tail reconnection site. In all, 5 dipolarizations are observed, each associated with the closure of ~0.1 GWb of flux. Very simple calculations indicate that the X-line should progress down-tail at a speed of 20 km s-1, or 6 RE between each dipolarization.
Optical characteristics of desert dust over the East Mediterranean during summer: a case study
Authors: Balis D. , Amiridis V. , Kazadzis S. , Papayannis A. , Tsaknakis G. , Tzortzakis S. , Kalivitis N. , Vrekoussis M. , Kanakidou M. , Mihalopoulos N. , Chourdakis G. , Nickovic S. , Pérez C. , Baldasano J. , Drakakis M. 
Published: June 2010

Abstract. High aerosol optical depth (AOD) values, larger than 0.6, are systematically observed in the Ultraviolet (UV) region both by sunphotometers and lidar systems over Greece during summertime. To study in more detail the characteristics and the origin of these high AOD values, a campaign took place in Greece in the frame of the PHOENICS (Particles of Human Origin Extinguishing Natural solar radiation In Climate Systems) and EARLINET (European Aerosol Lidar Network) projects during August–September of 2003, which included simultaneous sunphotometric and lidar measurements at three sites covering the north-south axis of Greece: Thessaloniki, Athens and Finokalia, Crete. Several events with high AOD values have been observed over the measuring sites during the campaign period, many of them corresponding to Saharan dust. In this paper we focused on the event of 30 and 31 August 2003, when a dust layer in the height range of 2000-5000 m, progressively affected all three stations. This layer showed a complex behavior concerning its spatial evolution and allowed us to study the changes in the optical properties of the desert dust particles along their transport due to aging and mixing with other types of aerosol. The extinction-to-backscatter ratio determined on the 30 August 2003 at Thessaloniki was approximately 50 sr, characteristic for rather spherical mineral particles, and the measured color index of 0.4 was within the typical range of values for desert dust. Mixing of the desert dust with other sources of aerosols resulted the next day in overall smaller and less absorbing population of particles with a lidar ratio of 20 sr. Mixing of polluted air-masses originating from Northern Greece and Crete and Saharan dust result in very high aerosol backscatter values reaching 7 Mm-1 sr-1 over Finokalia. The Saharan dust observed over Athens followed a different spatial evolution and was not mixed with the boundary layer aerosols mainly originating from local pollution.
A study of the ionogram derived effective scale height around the ionospheric &lt;I&gt;hm&lt;/I&gt;F2
Authors: Liu L. , Wan W. , Ning B. 
Published: June 2010

Abstract. The diurnal, seasonal, and solar activity variations of the ionogram derived scale height around the ionospheric F-layer peak (Hm) are statistically analyzed at Wuhan (114.4° E, 30.6° N) and the yearly variations of Hm are also investigated for Wuhan and 12 other stations where Hm data are available. Hm, as a measure of the slope of the topside electron number density profiles, is calculated from the bottomside electron density profiles derived from vertical sounding ionograms using the UMLCAR SAO-Explorer. Results indicate that the value of median Hm increases with increasing solar flux. Hm is highest in summer and lowest in winter during the daytime, while it exhibits a much smaller seasonal variation at night. A common feature presented at these 13 stations is that Hm undergoes a yearly annual variation with a maximum in summer during the daytime. The annual variation becomes much weaker or disappears from late night to pre-sunrise. In addition, a moderate positive correlation is found between Hm with hmF2 and a strong correlation between the bottomside thickness parameter B0 and Hm. The latter provides a new and convenient way for empirical modeling the topside ionospheric shape only from the established B0 parameter set.
STARE velocity at large flow angles: is it related to the ion acoustic speed?
Authors: Uspensky M. V. , Koustov A. V. , Nozawa S. 
Published: June 2010

Abstract. The electron drift and ion-acoustic speed in the E region inferred from EISCAT measurements are compared with concurrent STARE radar velocity data to investigate a recent hypothesis by Bahcivan et al. (2005), that the electrojet irregularity velocity at large flow angles is simply the product of the ion-acoustic speed and the cosine of an angle between the electron flow and the irregularity propagation direction. About 3000 measurements for flow angles of 50°–70° and electron drifts of 400–1500 m/s are considered. It is shown that the correlation coefficient and the slope of the best linear fit line between the predicted STARE velocity (based solely on EISCAT data and the hypothesis of Bahcivan et al. (2005)) and the measured one are both of the order of ~0.4. Velocity predictions are somewhat better if one assumes that the irregularity phase velocity is the line-of-sight component of the E×B drift scaled down by a factor ~0.6 due to off-orthogonality of irregularity propagation (nonzero effective aspect angles of STARE observations).
Selenium: Radionuclides
Authors: Shaw George , Ashworth Daniel 
Published: June 2010

AbstractSelenium in the environment has been studied intensively for several decades, since it is both a trace nutrient and a toxin. It is a ubiquitous element in soils, waters, and the atmosphere, with chemical similarities to the other group 16 elements sulfur, polonium, and tellurium. Important selenium species in environmental media include inorganic oxyanions as well as organic species produced by biological methylation mechanisms. The only probable long‐term source of radioactive selenium to the environment is the leakage from radioactive waste repositories. Only79Se is of concern in this respect, since it is the only long‐lived radioactive isotope of selenium (physical half‐life = 377 000 years). Under alkaline geochemical conditions, there is the potential for79Se to migrate from geological radioactive waste repositories in very small quantities over very long periods. It is expected that any79Se released into the environment will behave in the same way as nonradioactive selenium, though the kinetics of isotopic exchange between79Se and stable selenium in soils, sediments, and other environmental media have never been studied over timescales relevant to radioactive waste disposal. It is unlikely that environmental concentrations of79Se will ever lead to exposures approaching the intake levels associated with stable selenium. Any exposure that does occur is likely to be primarily through the dietary intake pathway, since the principal environmental reservoirs, and therefore potential sources, of selenium in the environment are waters and soils.
Breakdown of Casimir invariance in curved space‐time
Authors: Singh D. , Mobed N. 
Published: June 2010

AbstractIt is shown that the commonly accepted definition for the Casimir scalar operators of the Poincaré group does not satisfy the properties of Casimir invariance when applied to the non‐inertial motion of particles while in the presence of external gravitational and electromagnetic fields, where general curvilinear co‐ordinates are used to describe the momentum generators within a Fermi normal co‐ordinate framework. Specific expressions of the Casimir scalar properties are presented. While the Casimir scalar for linear momentum remains Lorentz invariant in the absence of external fields, this is no longer true for the spin Casimir scalar. Potential implications are considered for the propagation of photons, gravitons, and gravitinos as described by the spin‐3/2 Rarita‐Schwinger vector‐spinor field. In particular, it is shown that non‐inertial motion introduces a frame‐based effective mass to the spin interaction, with interesting physical consequences that are explored in detail.
Morphology development and non‐isothermal crystallization behavior of polyamide 11/ethylene‐vinyl alcohol blends
Authors: Li Yingchun , Hu Guosheng , Wang Biaobing 
Published: June 2010

AbstractHigh‐barrier polyamide 11 (PA11) was prepared by in situ co‐crosslinking technology using ethylene‐vinyl alcohol (EVOH) as the barrier layer, and the morphology development and non‐isothermal crystallization behavior were investigated. The scanning electron microscope (SEM) observations demonstrated that the morphology development was greatly dependent on the concentration of dicumyl peroxide (DCP). A pronounced lamellar morphology was obtained at 1.5% DCP loading level. The analysis of non‐isothermal crystallization kinetics indicated that the addition of EVOH and DCP affected the crystallization mode of PA 11. Notably, the crystallization rate of PA 11 was related with the morphology of EVOH and the interaction between EVOH and PA 11. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010