for Journals by Title or ISSN
for Articles by Keywords
help
  Subjects -> PHYSICS (Total: 775 journals)
    - ELECTRICITY AND MAGNETISM (8 journals)
    - MECHANICS (19 journals)
    - NUCLEAR PHYSICS (47 journals)
    - OPTICS (90 journals)
    - PHYSICS (564 journals)
    - SOUND (19 journals)
    - THERMODYNAMICS (28 journals)

PHYSICS (564 journals)                  1 2 3 4 5 6 | Last

Acta Acustica united with Acustica     Full-text available via subscription   (Followers: 7)
Acta Mechanica     Hybrid Journal   (Followers: 15)
Advanced Composite Materials     Hybrid Journal   (Followers: 16)
Advanced Functional Materials     Hybrid Journal   (Followers: 39)
Advanced Materials     Hybrid Journal   (Followers: 413)
Advanced Science Focus     Free  
Advances in Condensed Matter Physics     Open Access   (Followers: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
Advances in Geophysics     Full-text available via subscription   (Followers: 5)
Advances in High Energy Physics     Open Access   (Followers: 12)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 3)
Advances in Materials Physics and Chemistry     Open Access   (Followers: 16)
Advances in Natural Sciences: Nanoscience and Nanotechnology     Open Access   (Followers: 14)
Advances in OptoElectronics     Open Access   (Followers: 3)
Advances In Physics     Hybrid Journal   (Followers: 9)
Advances in Physics Theories and Applications     Open Access   (Followers: 8)
Advances in Remote Sensing     Open Access   (Followers: 9)
AIP Advances     Open Access   (Followers: 6)
AIP Conference Proceedings     Full-text available via subscription   (Followers: 2)
American Journal of Applied Sciences     Open Access   (Followers: 32)
American Journal of Condensed Matter Physics     Open Access   (Followers: 5)
American Journal of Signal Processing     Open Access   (Followers: 8)
Analysis and Mathematical Physics     Hybrid Journal   (Followers: 2)
Annalen der Physik     Hybrid Journal   (Followers: 3)
Annales Geophysicae (ANGEO)     Open Access   (Followers: 4)
Annales Henri PoincarĂ©     Hybrid Journal   (Followers: 1)
Annales UMCS, Physica     Open Access  
Annals of Nuclear Medicine     Hybrid Journal   (Followers: 3)
Annals of Physics     Hybrid Journal   (Followers: 3)
Annals of West University of Timisoara - Physics     Open Access  
Annual Reports on NMR Spectroscopy     Full-text available via subscription   (Followers: 1)
Annual Review of Analytical Chemistry     Full-text available via subscription   (Followers: 9)
Annual Review of Condensed Matter Physics     Full-text available via subscription   (Followers: 1)
Annual Review of Materials Research     Full-text available via subscription   (Followers: 4)
APL Materials     Open Access   (Followers: 6)
Applied Composite Materials     Hybrid Journal   (Followers: 9)
Applied Physics A     Hybrid Journal   (Followers: 9)
Applied Physics Frontier     Open Access   (Followers: 1)
Applied Physics Letters     Hybrid Journal   (Followers: 26)
Applied Physics Research     Open Access   (Followers: 6)
Applied Physics Reviews     Hybrid Journal   (Followers: 8)
Applied Radiation and Isotopes     Hybrid Journal   (Followers: 5)
Applied Remote Sensing Journal     Open Access   (Followers: 10)
Applied Spectroscopy     Full-text available via subscription   (Followers: 13)
Applied Spectroscopy Reviews     Hybrid Journal   (Followers: 2)
Archive for Rational Mechanics and Analysis     Hybrid Journal   (Followers: 3)
Asia Pacific Physics Newsletter     Hybrid Journal  
ASTRA Proceedings     Open Access  
Astronomy & Geophysics     Hybrid Journal   (Followers: 2)
Astrophysical Journal Letters     Full-text available via subscription   (Followers: 3)
Astrophysical Journal Supplement Series     Full-text available via subscription   (Followers: 3)
Atoms     Open Access  
Attention, Perception & Psychophysics     Full-text available via subscription   (Followers: 9)
Autonomous Mental Development, IEEE Transactions on     Hybrid Journal   (Followers: 5)
Axioms     Open Access  
Bangladesh Journal of Medical Physics     Open Access  
Bauphysik     Hybrid Journal   (Followers: 1)
Biomaterials     Hybrid Journal   (Followers: 34)
Biomedical Engineering, IEEE Reviews in     Full-text available via subscription   (Followers: 16)
Biomedical Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 14)
Biomedical Imaging and Intervention Journal     Open Access   (Followers: 5)
Biophysical Reviews     Hybrid Journal  
Biophysical Reviews and Letters     Hybrid Journal   (Followers: 3)
BMC Biophysics     Open Access   (Followers: 7)
BMC Nuclear Medicine     Open Access   (Followers: 5)
Brazilian Journal of Physics     Hybrid Journal  
Broadcasting, IEEE Transactions on     Hybrid Journal   (Followers: 6)
Bulletin of Materials Science     Open Access   (Followers: 39)
Bulletin of the Atomic Scientists     Full-text available via subscription   (Followers: 4)
Bulletin of the Lebedev Physics Institute     Hybrid Journal   (Followers: 1)
Bulletin of the Russian Academy of Sciences: Physics     Hybrid Journal  
Caderno Brasileiro de Ensino de FĂ­sica     Open Access  
Canadian Journal of Physics     Full-text available via subscription   (Followers: 1)
Cells     Open Access   (Followers: 1)
Central European Journal of Physics     Hybrid Journal   (Followers: 1)
CERN courier. International journal of high energy physics     Free  
Chinese Journal of Astronomy and Astrophysics     Full-text available via subscription   (Followers: 1)
Chinese Journal of Chemical Physics     Hybrid Journal   (Followers: 1)
Chinese Physics B     Full-text available via subscription  
Chinese Physics C     Full-text available via subscription  
Chinese Physics Letters     Full-text available via subscription  
Cogent Physics     Open Access  
Cohesion and Structure     Full-text available via subscription   (Followers: 2)
Colloid Journal     Hybrid Journal   (Followers: 2)
Communications in Mathematical Physics     Hybrid Journal   (Followers: 2)
Communications in Numerical Methods in Engineering     Hybrid Journal   (Followers: 3)
Communications in Theoretical Physics     Full-text available via subscription   (Followers: 1)
Composites Part A : Applied Science and Manufacturing     Hybrid Journal   (Followers: 55)
Composites Part B : Engineering     Hybrid Journal   (Followers: 79)
Computational Astrophysics and Cosmology     Open Access  
Computational Materials Science     Hybrid Journal   (Followers: 19)
Computational Mathematics and Mathematical Physics     Hybrid Journal   (Followers: 1)
Computational Particle Mechanics     Hybrid Journal  
Computational Science and Discovery     Full-text available via subscription  
Computer Physics Communications     Hybrid Journal  
Contemporary Concepts of Condensed Matter Science     Full-text available via subscription  
Contemporary Physics     Hybrid Journal   (Followers: 12)
Continuum Mechanics and Thermodynamics     Hybrid Journal   (Followers: 3)
Contributions to Plasma Physics     Hybrid Journal   (Followers: 2)
COSPAR Colloquia Series     Full-text available via subscription   (Followers: 1)

        1 2 3 4 5 6 | Last

Journal Cover   Annales Geophysicae (ANGEO)
  [SJR: 1.176]   [H-I: 63]   [6 followers]  Follow
    
  This is an Open Access Journal Open Access journal
   ISSN (Print) 0992-7689 - ISSN (Online) 1432-0576
   Published by European Geosciences Union Homepage  [8 journals]
  • Additional acceleration of solar-wind particles in current sheets of the
           heliosphere

    • Abstract: Additional acceleration of solar-wind particles in current sheets of the heliosphere

      Annales Geophysicae, 33, 457-470, 2015

      Author(s): V. Zharkova and O. Khabarova

      Particles of fast solar wind in the vicinity of the heliospheric current sheet (HCS) or in a front of interplanetary coronal mass ejections (ICMEs) often reveal very peculiar energy or velocity profiles, density distributions with double or triple peaks, and well-defined streams of electrons occurring around or far away from these events. In order to interpret the parameters of energetic particles (both ions and electrons) measured by the WIND spacecraft during the HCS crossings, a comparison of the data was carried out with 3-D particle-in-cell (PIC) simulations for the relevant magnetic topology (Zharkova and Khabarova, 2012). The simulations showed that all the observed particle-energy distributions, densities, ion peak velocities, electron pitch angles and directivities can be fitted with the same model if the heliospheric current sheet is in a status of continuous magnetic reconnection. In this paper we present further observations of the solar-wind particles being accelerated to rather higher energies while passing through the HCS and the evidence that this acceleration happens well before the appearance of the corotating interacting region (CIR), which passes through the spacecraft position hours later. We show that the measured particle characteristics (ion velocity, electron pitch angles and the distance at which electrons are turned from the HCS) are in agreement with the simulations of additional particle acceleration in a reconnecting HCS with a strong guiding field as measured by WIND. A few examples are also presented showing additional acceleration of solar-wind particles during their passage through current sheets formed in a front of ICMEs. This additional acceleration at the ICME current sheets can explain the anticorrelation of ion and electron fluxes frequently observed around the ICME's leading front. Furthermore, it may provide a plausible explanation of the appearance of bidirectional "strahls" (field-aligned most energetic suprathermal electrons) at the leading edge of ICMEs as energetic electrons generated during a magnetic reconnection at the ICME-front current sheet.
      PubDate: 2015-04-09T00:00:00+02:00
       
  • Global variation in the long-term seasonal changes observed in ionospheric
           F region data

    • Abstract: Global variation in the long-term seasonal changes observed in ionospheric F region data

      Annales Geophysicae, 33, 449-455, 2015

      Author(s): C. J. Scott and R. Stamper

      Long-term variability has previously been observed in the relative magnitude of annual and semi-annual variations in the critical frequency (related to the peak electron concentration) of the ionospheric F2 layer (foF2). In this paper we investigate the global patterns in such variability by calculating the time varying power ratio of semi-annual to annual components seen in ionospheric foF2 data sequences from 77 ionospheric monitoring stations around the world. The temporal variation in power ratios observed at each station was then correlated with the same parameter calculated from similar epochs for the Slough/Chilton data set (for which there exists the longest continuous sequence of ionospheric data). This technique reveals strong regional variation in the data, which bears a striking similarity to the regional variation observed in long-term changes to the height of the ionospheric F2 layer. We argue that since both the height and peak density of the ionospheric F2 region are influenced by changes to thermospheric circulation and composition, the observed long-term and regional variability can be explained by such changes. In the absence of long-term measurements of thermospheric composition, detailed modelling work is required to investigate these processes.
      PubDate: 2015-04-08T00:00:00+02:00
       
  • The dayside magnetopause location during radial interplanetary magnetic
           field periods: Cluster observation and model comparison

    • Abstract: The dayside magnetopause location during radial interplanetary magnetic field periods: Cluster observation and model comparison

      Annales Geophysicae, 33, 437-448, 2015

      Author(s): T. Huang, H. Wang, J.-H. Shue, L. Cai, and G. Pi

      The present work has investigated the midlatitudinal magnetopause locations under radial interplanetary field (RIMF) conditions. Among 262 (256) earthward (sunward) RIMF events from years of 2001 to 2009, Cluster satellites have crossed the magnetopause 22(12) times, with 10 (7) events occurring at midlatitudes. The observed midlatitudinal magnetopause positions are compared with two empirical magnetopause models (Shue et al., 1998; Boardsen et al., 2000) (hereafter referred to as the Shue98 model and the Boardsen00 model). The observation–model differences exhibit local time asymmetry. For earthward RIMF cases, the Shue98 model underestimates the magnetopause positions in the postnoon sector, while it overestimates the magnetopause positions in the dawn and dusk sectors. The Boardsen00 model generally underestimates the magnetopause after 6 MLT (magnetic local time), with larger deviations in the postnoon sector as compared to those in the prenoon. For sunward RIMF cases, the selected events are mainly clustered around the dawn and dusk sectors. The comparison with the Shue98 model indicates contractions in the dawn and expansions in the dusk sector, while the comparison with Boardsen00 indicates general expansions, with larger expansions in the later local time sectors. The local time variations in the differences between observations and the Shue98 and the Boardsen00 models indicate that the real magnetopause could be asymmetrically shaped during radial IMF periods, which should be considered by magnetopause models. The observation–model differences in the magnetopause positions (Δ RMP) during RIMF periods correlate well with the solar wind dynamic pressure, with larger Δ RMP for larger Pd. The southern magnetopause expands further outward relative to the model prediction when the dipole tilt angle is more negative (local summer in the Southern Hemisphere). For earthward RIMF cases, the generally good correlations between Δ RMP and the IMF cone angle are consistent with the previous hypothesis (Dušík et al., 2010) that, with more radial IMF, the subsolar magnetopause will expand further outward, owever, this is not the case for the comparison with Boardsen00 during sunward IMF periods, as it shows less dependence on the IMF cone angle.
      PubDate: 2015-04-02T00:00:00+02:00
       
  • Transitions between states of magnetotail–ionosphere coupling and
           the role of solar wind dynamic pressure: the 25 July 2004 interplanetary
           CME case

    • Abstract: Transitions between states of magnetotail–ionosphere coupling and the role of solar wind dynamic pressure: the 25 July 2004 interplanetary CME case

      Annales Geophysicae, 33, 427-436, 2015

      Author(s): P. E. Sandholt, C. J. Farrugia, and W. F. Denig

      In a case study, we investigate transitions between fundamental magnetosphere–ionosphere (M-I) coupling modes during storm-time conditions (SYM-H between −100 and −160 nT) driven by an interplanetary coronal mass ejection (ICME). We combine observations from the near tail, at geostationary altitude (GOES-10), and electrojet activities across the auroral oval at postnoon-to-dusk and midnight. After an interval of strong westward electrojet (WEJ) activity, a 3 h long state of attenuated/quenched WEJ activity was initiated by abrupt drops in the solar wind density and dynamic pressure. The attenuated substorm activity consisted of brief phases of magnetic field perturbation and electron flux decrease at GOES-10 near midnight and moderately strong conjugate events of WEJ enhancements at the southern boundary of the oval, as well as a series of very strong eastward electrojet (EEJ) events at dusk, during a phase of enhanced ring current evolution, i.e., enhanced SYM-H deflection within −120 to −150 nT. Each of these M-I coupling events was preceded by poleward boundary intensifications and auroral streamers at higher oval latitudes. We identify this mode of attenuated substorm activity as being due to a magnetotail state characterized by bursty reconnection and bursty bulk flows/dipolarization fronts (multiple current wedgelets) with associated injection dynamo in the near tail, in their braking phase. The latter process is associated with activations of the Bostrøm type II (meridional) current system. A transition to the next state of M-I coupling, when a full substorm expansion took place, was triggered by an abrupt increase of the ICME dynamic pressure from 1 to 5 nPa. The brief field deflection events at GOES-10 were then replaced by a 20 min long interval of extreme field stretching (Bz approaching 5 nT and Bx ≈ 100 nT) followed by a major dipolarization (Δ Bz ≈ 100 nT). In the ionosphere the latter stage appeared as a "full-size" stepwise poleward expansion of the WEJ. It thus appears that the ICME passage led to fundamentally different M-I coupling states corresponding to different levels of dynamic pressure (Pdyn) under otherwise very similar ICME conditions. Full WEJ activity, covering a wide latitude range across the auroral oval in the midnight sector, was attenuated by the abrupt dynamic pressure decrease and resumed after the subsequent abrupt increase.
      PubDate: 2015-04-01T00:00:00+02:00
       
  • Terrestrial exospheric hydrogen density distributions under solar minimum
           and solar maximum conditions observed by the TWINS stereo mission

    • Abstract: Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission

      Annales Geophysicae, 33, 413-426, 2015

      Author(s): J. H. Zoennchen, U. Nass, and H. J. Fahr

      Circumterrestrial Lyman-α column brightness observations above 3 Earth radii (Re) have been used to derive separate 3-D neutral hydrogen density models of the Earth's exosphere for solar minimum (2008, 2010) and near-solar-maximum (2012) conditions. The data used were measured by Lyman-α detectors (LAD1/2) onboard each of the TWINS satellites from very different orbital positions with respect to the exosphere. Exospheric H atoms resonantly scatter the near-line-center solar Lyman-α flux at 121.6 nm. Assuming optically thin conditions above 3Re along a line of sight (LOS), the scattered LOS-column intensity is proportional to the LOS H-column density. We found significant differences in the density distribution of the terrestrial exosphere under different solar conditions. Under solar maximum conditions we found higher H densities and a larger spatial extension compared to solar minimum. After a continuous, 2-month decrease in (27 day averaged) solar activity, significantly lower densities were found. Differences in shape and orientation of the exosphere under different solar conditions exist. Above 3 Re, independent of solar activity, increased H densities appear on the Earth's nightside shifted towards dawn. With increasing distance (as measured at 8Re) this feature is shifted westward/duskward by between −4 and −5° with respect to midnight. Thus, at larger geocentric distance the exosphere seems to be aligned with the aberrated Earth–solar-wind line, defined by the solar wind velocity and the orbital velocity of the Earth. The results presented in this paper are valid for geocentric distances between 3 and 8Re.
      PubDate: 2015-03-27T00:00:00+01:00
       
  • Online NARMAX model for electron fluxes at GEO

    • Abstract: Online NARMAX model for electron fluxes at GEO

      Annales Geophysicae, 33, 405-411, 2015

      Author(s): R. J. Boynton, M. A. Balikhin, and S. A. Billings

      Multi-input single-output (MISO) nonlinear autoregressive moving average with exogenous inputs (NARMAX) models have been derived to forecast the > 0.8 MeV and > 2 MeV electron fluxes at geostationary Earth orbit (GEO). The NARMAX algorithm is able to identify mathematical model for a wide class of nonlinear systems from input–output data. The models employ solar wind parameters as inputs to provide an estimate of the average electron flux for the following day, i.e. the 1-day forecast. The identified models are shown to provide a reliable forecast for both > 0.8 and > 2 MeV electron fluxes and are capable of providing real-time warnings of when the electron fluxes will be dangerously high for satellite systems. These models, named SNB3GEO > 0.8 and > 2 MeV electron flux models, have been implemented online at http://www.ssg.group.shef.ac.uk/USSW/UOSSW.html.
      PubDate: 2015-03-27T00:00:00+01:00
       
  • Are dayside long-period pulsations related to the cusp?

    • Abstract: Are dayside long-period pulsations related to the cusp?

      Annales Geophysicae, 33, 395-404, 2015

      Author(s): V. Pilipenko, V. Belakhovsky, M. J. Engebretson, A. Kozlovsky, and T. Yeoman

      We compare simultaneous observations of long-period ultra-low-frequency (ULF) wave activity from a Svalbard/IMAGE fluxgate magnetometer latitudinal profile covering the expected cusp geomagnetic latitudes. Irregular Pulsations at Cusp Latitudes (IPCL) and narrowband Pc5 waves are found to be a ubiquitous element of ULF activity in the dayside high-latitude region. To identify the ionospheric projections of the cusp, we use the width of return signal of the Super Dual Auroral Radar Network (SuperDARN) radar covering the Svalbard archipelago, predictions of empirical cusp models, augmented whenever possible by Defense Meteorological Satellite Program (DMSP) identification of magnetospheric boundary domains. The meridional spatial structure of broadband dayside Pc5–6 pulsation spectral power has been found to have a localized latitudinal peak, not under the cusp proper as was previously thought, but several degrees southward from the equatorward cusp boundary. The earlier claims of the dayside monochromatic Pc5 wave association with the open–closed boundary also seems doubtful. Transient currents producing broadband Pc5–6 probably originate at the low-latitude boundary layer/central plasma sheet (LLBL/CPS) interface, though such identification with available DMSP data is not very precise. The occurrence of broadband Pc5–6 pulsations in the dayside boundary layers is a challenge to modelers because so far their mechanism has not been firmly identified.
      PubDate: 2015-03-24T00:00:00+01:00
       
  • Contribution of proton and electron precipitation to the observed electron
           concentration in October–November 2003 and September 2005

    • Abstract: Contribution of proton and electron precipitation to the observed electron concentration in October–November 2003 and September 2005

      Annales Geophysicae, 33, 381-394, 2015

      Author(s): P. T. Verronen, M. E. Andersson, A. Kero, C.-F. Enell, J. M. Wissing, E. R. Talaat, K. Kauristie, M. Palmroth, T. E. Sarris, and E. Armandillo

      Understanding the altitude distribution of particle precipitation forcing is vital for the assessment of its atmospheric and climate impacts. However, the proportion of electron and proton forcing around the mesopause region during solar proton events is not always clear due to uncertainties in satellite-based flux observations. Here we use electron concentration observations of the European Incoherent Scatter Scientific Association (EISCAT) incoherent scatter radars located at Tromsø (69.58° N, 19.23° E) to investigate the contribution of proton and electron precipitation to the changes taking place during two solar proton events. The EISCAT measurements are compared to the results from the Sodankylä Ion and Neutral Chemistry Model (SIC). The proton ionization rates are calculated by two different methods – a simple energy deposition calculation and the Atmospheric Ionization Model Osnabrück (AIMOS v1.2), the latter providing also the electron ionization rates. Our results show that in general the combination of AIMOS and SIC is able to reproduce the observed electron concentration within ± 50% when both electron and proton forcing is included. Electron contribution is dominant above 90 km, and can contribute significantly also in the upper mesosphere especially during low or moderate proton forcing. In the case of strong proton forcing, the AIMOS electron ionization rates seem to suffer from proton contamination of satellite-based flux data. This leads to overestimation of modelled electron concentrations by up to 90% between 75–90 km and up to 100–150% at 70–75 km. Above 90 km, the model bias varies significantly between the events. Although we cannot completely rule out EISCAT data issues, the difference is most likely a result of the spatio-temporal fine structure of electron precipitation during individual events that cannot be fully captured by sparse in situ flux (point) measurements, nor by the statistical AIMOS model which is based upon these observations.
      PubDate: 2015-03-23T00:00:00+01:00
       
  • Observation of electron biteout regions below sporadic E layers at polar
           latitudes

    • Abstract: Observation of electron biteout regions below sporadic E layers at polar latitudes

      Annales Geophysicae, 33, 371-380, 2015

      Author(s): G. A. Lehmacher, M. F. Larsen, and C. L. Croskey

      The descent of a narrow sporadic E layer near 95 km altitude over Poker Flat Research Range in Alaska was observed with electron probes on two consecutive sounding rockets and with incoherent scatter radar during a 2 h period near magnetic midnight. A series of four trimethyl aluminum chemical releases demonstrated that the Es layer remained just slightly above the zonal wind node, which was slowly descending due to propagating long-period gravity waves. The location of the layer is consistent with the equilibrium position due to combined action of the wind shear and electric fields. Although the horizontal electric field could not be measured directly, we estimate that it was ~ 2 mV m−1 southward, consistent with modeling the vertical ion drift, and compatible with extremely quiet conditions. Both electron probes observed deep biteout regions just below the Es enhancements, which also descended with the sporadic layers. We discuss several possibilities for the cause of these depletions; one possibility is the presence of negatively charged, nanometer-sized mesospheric smoke particles. Such particles have recently been detected in the upper mesosphere, but not yet in immediate connection with sporadic E. Our observations of electron depletions suggest a new process associated with sporadic E.
      PubDate: 2015-03-20T00:00:00+01:00
       
  • Long-term midlatitude mesopause region temperature trend deduced from
           quarter century (1990–2014) Na lidar observations

    • Abstract: Long-term midlatitude mesopause region temperature trend deduced from quarter century (1990–2014) Na lidar observations

      Annales Geophysicae, 33, 363-369, 2015

      Author(s): C.-Y. She, D. A. Krueger, and T. Yuan

      The long-term midlatitude temperature trend between 85 and 105 km is deduced from 25 years (March 1990–December 2014) of Na Lidar observations. With a strong warming episode in the 1990s, the time series was least-square fitted to an 11-parameter nonlinear function. This yields a cooling trend starting from an insignificant value of 0.64 ± 0.99 K decade−1 at 85 km, increasing to a maximum of 2.8 ± 0.58 K decade−1 between 91 and 93 km, and then decreasing to a warming trend above 103 km. The geographic altitude dependence of the trend is in general agreement with model predictions. To shed light on the nature of the warming episode, we show that the recently reported prolonged global surface temperature cooling after the Mt Pinatubo eruption can also be very well represented by the same response function.
      PubDate: 2015-03-19T00:00:00+01:00
       
  • Comparison of aerosol extinction between lidar and SAGE II over Gadanki, a
           tropical station in India

    • Abstract: Comparison of aerosol extinction between lidar and SAGE II over Gadanki, a tropical station in India

      Annales Geophysicae, 33, 351-362, 2015

      Author(s): P. Kulkarni and S. Ramachandran

      An extensive comparison of aerosol extinction has been performed using lidar and Stratospheric Aerosol and Gas Experiment (SAGE) II data over Gadanki (13.5° N, 79.2° E), a tropical station in India, following coincident criteria during volcanically quiescent conditions from 1998 to 2005. The aerosol extinctions derived from lidar are higher than SAGE II during all seasons in the upper troposphere (UT), while in the lower-stratosphere (LS) values are closer. The seasonal mean percent differences between lidar and SAGE II aerosol extinctions are > 100% in the UT and < 50% above 25 km. Different techniques (point and limb observations) played the major role in producing the observed differences. SAGE II aerosol extinction in the UT increases as the longitudinal coverage is increased as the spatial aerosol extent increases, while similar extinction values in LS confirm the zonal homogeneity of LS aerosols. The study strongly emphasized that the best meteorological parameters close to the lidar measurement site in terms of space and time and Ba (sr−1), the ratio between aerosol backscattering and extinction, are needed for the tropics for a more accurate derivation of aerosol extinction.
      PubDate: 2015-03-18T00:00:00+01:00
       
  • Adaptation of the de Hoffmann–Teller frame for quasi-perpendicular
           collisionless shocks

    • Abstract: Adaptation of the de Hoffmann–Teller frame for quasi-perpendicular collisionless shocks

      Annales Geophysicae, 33, 345-350, 2015

      Author(s): H. Comişel, Y. Narita, and U. Motschmann

      The concept of the de Hoffmann–Teller frame is revisited for a high Mach-number quasi-perpendicular collisionless shock wave. Particle-in-cell simulation shows that the local magnetic field oscillations in the shock layer introduce a residual motional electric field in the de Hoffmann–Teller frame, which is misleading in that one may interpret that electrons were not accelerated but decelerated in the shock layer. We propose the concept of the adaptive de Hoffmann–Teller (AHT) frame in which the residual convective field is canceled by modulating the sliding velocity of the de Hoffmann–Teller frame. The electrostatic potential evaluated by Liouville mapping supports the potential profile obtained by electric field in this adaptive frame, offering a wide variety of applications in shock wave studies.
      PubDate: 2015-03-17T00:00:00+01:00
       
  • Modeling of rain attenuation and site diversity predictions for tropical
           regions

    • Abstract: Modeling of rain attenuation and site diversity predictions for tropical regions

      Annales Geophysicae, 33, 321-331, 2015

      Author(s): F. A. Semire, R. Mohd-Mokhtar, W. Ismail, N. Mohamad, and J. S. Mandeep

      Presented in this paper is an empirical model for long-term rain attenuation prediction and statistical prediction of site diversity gain on a slant path. Rain attenuation prediction on a slant path is derived using data collected from tropical regions, and the formula proposed is based on Gaussian distribution. The proposed rain attenuation model shows a considerable reduction in prediction error in terms of standard deviation and root-mean-square (rms) error. The site diversity prediction model is derived as a function of site separation distance, frequency of operation, elevation angle and baseline orientation angle. The novelty of the model is the inclusion of low elevation angles and a high link frequency up to 70 GHz in the model derivation. The results of comparison with Hodge, Panagopoulos and Nagaraja empirical predictions show that the proposed model provides a better performance for site separation distance and elevation angle. The overall performance of the proposed site diversity model is good, and the percentage error is within the allowable error limit approved by International Telecommunication Union – Region (ITU-R).
      PubDate: 2015-03-17T00:00:00+01:00
       
  • Outflow of low-energy O+ ion beams observed during
           periods without substorms

    • Abstract: Outflow of low-energy O+ ion beams observed during periods without substorms

      Annales Geophysicae, 33, 333-344, 2015

      Author(s): G. K. Parks, E. Lee, S. Y. Fu, M. Fillingim, I. Dandouras, Y. B. Cui, J. Hong, and H. Rème

      Numerous observations have shown that ions flow out of the ionosphere during substorms with more fluxes leaving as the substorm intensity increases (Wilson et al., 2004). In this article we show observations of low-energy (few tens of electron volts) ionospheric ions flowing out periods without substorms, determined using the Wideband Imaging Camera (WIC) and Auroral Electrojet (AE) indices. We use Cluster ion composition data and show the outflowing ions are field-aligned H+, He+ and O+ beams accelerated to energies of ~40–80 eV, after correcting for spacecraft potential. The estimated fluxes of the low-energy O+ ions measured at ~20 000 km altitude are >103–105 cm−2 s. Assuming the auroral oval is the source of the escaping ions, the measured fluxes correspond to a flow rate of ~1019–1021 ions s−1 leaving the ionosphere. However, periods without substorms can persist for hours suggesting the low-energy ions flowing out during these times could be a major source of the heavy ion population in the plasma sheet and lobe.
      PubDate: 2015-03-17T00:00:00+01:00
       
  • Coupling in the middle atmosphere related to the 2013 major sudden
           stratospheric warming

    • Abstract: Coupling in the middle atmosphere related to the 2013 major sudden stratospheric warming

      Annales Geophysicae, 33, 309-319, 2015

      Author(s): R. J. de Wit, R. E. Hibbins, P. J. Espy, and E. A. Hennum

      The previously reported observation of anomalous eastward gravity wave forcing at mesopause heights around the onset of the January 2013 major sudden stratospheric warming (SSW) over Trondheim, Norway (63° N, 10° E), is placed in a global perspective using Microwave Limb Sounder (MLS) temperature observations from the Aura satellite. It is shown that this anomalous forcing results in a clear cooling over Trondheim about 10 km below mesopause heights. Conversely, near the mesopause itself, where the gravity wave forcing was measured, observations with meteor radar, OH airglow and MLS show no distinct cooling. Polar cap zonal mean temperatures show a similar vertical profile. Longitudinal variability in the high northern-latitude mesosphere and lower thermosphere (MLT) is characterized by a quasi-stationary wave-1 structure, which reverses phase at altitudes below ~ 0.1 hPa. This wave-1 develops prior to the SSW onset, and starts to propagate westward at the SSW onset. The latitudinal pole-to-pole temperature structure associated with the major SSW shows a warming (cooling) in the winter stratosphere (mesosphere) which extends to about 40° N. In the stratosphere, a cooling extending over the equator and far into the summer hemisphere is observed, whereas in the mesosphere an equatorial warming is noted. In the Southern Hemisphere mesosphere, a warm anomaly overlaying a cold anomaly is present, which is shown to propagate downward in time. This observed structure is in accordance with the temperature perturbations predicted by the proposed interhemispheric coupling mechanism for cases of increased winter stratospheric planetary wave activity, of which major SSWs are an extreme case. These results provide observational evidence for the interhemispheric coupling mechanism, and for the wave-mean flow interaction believed to be responsible for the establishment of the anomalies in the summer hemisphere.
      PubDate: 2015-03-11T00:00:00+01:00
       
  • O+ transport in the dayside magnetosheath and its
           dependence on the IMF direction

    • Abstract: O+ transport in the dayside magnetosheath and its dependence on the IMF direction

      Annales Geophysicae, 33, 301-307, 2015

      Author(s): R. Slapak, H. Nilsson, L. G. Westerberg, and R. Larsson

      Recent studies have shown that the escape of oxygen ions (O+) into the magnetosheath along open magnetic field lines from the terrestrial cusp and mantle is significant. We present a study of how O+ transport in the dayside magnetosheath depends on the interplanetary magnetic field (IMF) direction. There are clear asymmetries in the O+ flows for southward and northward IMF. The asymmetries can be understood in terms of the different magnetic topologies that arise due to differences in the location of the reconnection site, which depends on the IMF direction. During southward IMF, most of the observed magnetosheath O+ is transported downstream. In contrast, for northward IMF we observe O+ flowing both downstream and equatorward towards the opposite hemisphere. We observe evidence of dual-lobe reconnection occasionally taking place during strong northward IMF conditions, a mechanism that may trap O+ and bring it back into the magnetosphere. Its effect on the overall escape is however small: we estimate the upper limit of trapped O+ to be 5%, a small number considering that ion flux calculations are rough estimates. The total O+ escape flux is higher by about a factor of 2 during times of southward IMF, in agreement with earlier studies of O+ cusp outflow.
      PubDate: 2015-03-09T00:00:00+01:00
       
  • Stimulated electromagnetic emission polarization under different
           polarizations of pump waves

    • Abstract: Stimulated electromagnetic emission polarization under different polarizations of pump waves

      Annales Geophysicae, 33, 295-300, 2015

      Author(s): E. D. Tereshchenko, R. Y. Yurik, and L. Baddeley

      The results of investigations into the stimulated electromagnetic emission (SEE) polarization under different modes of the pump wave polarization are presented. The present results were obtained in November 2012 during a heating campaign utilizing the SPEAR (Space Plasma Exploration by Active Radar) heating facility, transmitting in both O- and X-mode polarization, and a PGI (Polar Geophysical Institute) radio interferometer capable of recording the polarization of the received radiation. The polarization ellipse parameters of the SEE DM (downshifted maximum) components were determined under both O-mode and X-mode polarization of the pump waves. The polarization direction of the SEE DM component was preserved under different polarizations of the pump waves. Different polarizations of the pump waves have a different SEE generation efficiency. The intensity of the DM component is observed to be greater during O-mode pumping. In addition, the numbers of observed SEE features are also greater during O-mode pumping.
      PubDate: 2015-03-05T00:00:00+01:00
       
  • Long-term response of stratospheric ozone and temperature to solar
           variability

    • Abstract: Long-term response of stratospheric ozone and temperature to solar variability

      Annales Geophysicae, 33, 267-277, 2015

      Author(s): I. Bordi, F. Berrilli, and E. Pietropaolo

      The long-term variability in stratospheric ozone mass mixing ratio (O3) and temperature (T) from 1979 to 2013 is investigated using the latest reanalysis product delivered by the European Centre for Medium-Range Weather Forecasts (ECMWF), i.e., ERA-Interim. Moreover, using the Mg II index time series for the same time period, the response of the stratosphere to the 11-year Schwabe solar cycle is investigated. Results reveal the following features: (i) upward (downward) trends characterize zonally averaged O3 anomalies in the upper (middle to lower stratosphere) stratosphere, while prevailing downward trends affect the T field. Mg II index data exhibit a weaker 24th solar cycle (though not complete) when compared with the previous two; (ii) correlations between O3 and Mg II, T and Mg II, and O3 and T are consistent with photochemical reactions occurring in the stratosphere and large-scale transport; and (iii) wavelet cross-spectra between O3 and Mg II index show common power for the 11-year period, particularly in tropical regions around 30–50 hPa, and different relative phase in the upper and lower stratosphere. A comprehensive insight into the actual processes accounting for the observed correlation between ozone and solar UV variability would be gained from an improved bias correction of ozone measurements provided by different satellite instruments, and from the observations of the time behavior of the solar spectral irradiance.
      PubDate: 2015-03-04T00:00:00+01:00
       
  • Vlasov simulations of trapping and loss of auroral electrons

    • Abstract: Vlasov simulations of trapping and loss of auroral electrons

      Annales Geophysicae, 33, 279-293, 2015

      Author(s): H. Gunell, L. Andersson, J. De Keyser, and I. Mann

      The plasma on an auroral field line is simulated using a Vlasov model. In the initial state, the acceleration region extends from one to three Earth radii in altitude with about half of the acceleration voltage concentrated in a stationary double layer at the bottom of this region. A population of electrons is trapped between the double layer and their magnetic mirror points at lower altitudes. A simulation study is carried out to examine the effects of fluctuations in the total accelerating voltage, which may be due to changes in the generator or the load of the auroral current circuit. The electron distribution function on the high potential side of the double layer changes significantly depending on whether the perturbation is toward higher or lower voltages, and therefore measurements of electron distribution functions provide information about the recent history of the voltage. Electron phase space holes are seen as a result of the induced fluctuations. Most of the voltage perturbation is assumed by the double layer. Hysteresis effects in the position of the double layer are observed when the voltage first is lowered and then brought back to its initial value.
      PubDate: 2015-03-04T00:00:00+01:00
       
  • Magnetic field-aligned plasma currents in gravitational fields

    • Abstract: Magnetic field-aligned plasma currents in gravitational fields

      Annales Geophysicae, 33, 257-266, 2015

      Author(s): O. E. Garcia, E. Leer, H. L. Pécseli, and J. K. Trulsen

      Analytical models are presented for currents along vertical magnetic field lines due to slow bulk electron motion in plasmas subject to a gravitational force. It is demonstrated that a general feature of this problem is a singularity in the plasma pressure force that develops at some finite altitude when a plasma that is initially in static equilibrium is set into slow motion. Classical fluid models thus do not allow general steady-state solutions for field-aligned currents. General solutions have to be non-stationary, varying on time scales of many periods of a plasma equivalent to the Brunt–Väisälä frequency. Except for very special choices of parameters, a steady-state solution exists only in an average sense. The conditions at large altitudes turn out to be extremely sensitive to even small changes in parameters at low altitudes. Low frequency fluctuations detected at large altitudes in the polar regions need not be caused by local low frequency instabilities, but merely reflect small fluctuations in conditions at low altitudes.
      PubDate: 2015-03-03T00:00:00+01:00
       
 
 
JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327
 
About JournalTOCs
API
Help
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-2015