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PHYSICS (563 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: 408)
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     Open Access  
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: 12)
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: 5)
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  
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)
Cryogenics     Hybrid Journal   (Followers: 18)

        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]
  • 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

    • 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

    • 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
  • Azimuthal velocity shear within an Earthward fast flow – further
           evidence for magnetotail untwisting?

    • Abstract: Azimuthal velocity shear within an Earthward fast flow – further evidence for magnetotail untwisting?

      Annales Geophysicae, 33, 245-255, 2015

      Author(s): T. Pitkänen, M. Hamrin, P. Norqvist, T. Karlsson, H. Nilsson, A. Kullen, S. M. Imber, and S. E. Milan

      It is well known that nonzero interplanetary magnetic field By conditions lead to a twisted magnetotail configuration. The plasma sheet is rotated around its axis and tail magnetic field lines are twisted, which causes an azimuthal displacement of their ionospheric footprints. According to the untwisting hypothesis, the untwisting of twisted field lines is suggested to influence the azimuthal direction of convective fast flows in the nightside geospace. However, there is a lack of in situ magnetospheric observations, which show actual signatures of the possible untwisting process. In this paper, we report detailed Cluster observations of an azimuthal flow shear across the neutral sheet associated with an Earthward fast flow on 5 September 2001. The observations show a flow shear velocity pattern with a V⊥y sign change, near the neutral sheet (Bx~0) within a fast flow during the neutral sheet flapping motion over the spacecraft. Firstly, this implies that convective fast flows may not generally be unidirectional across the neutral sheet, but may have a more complex structure. Secondly, in this event tail By and the flow shear are as expected by the untwisting hypothesis. The analysis of the flow shear reveals a linear dependence between Bx and V⊥y close to the neutral sheet and suggests that Cluster crossed the neutral sheet in the dawnward part of the fast flow channel. The magnetospheric observations are supported by the semi-empirical T96 and TF04 models. Furthermore, the ionospheric SuperDARN convection maps support the satellite observations proposing that the azimuthal component of the magnetospheric flows is enforced by a magnetic field untwisting. In summary, the observations give strong supportive evidence to the tail untwisting hypothesis. However, the T96 ionospheric mapping demonstrates the limitations of the model in mapping from a twisted tail.
      PubDate: 2015-03-03T00:00:00+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
  • A solar-wind-driven empirical model of Pc3 wave activity at a mid-latitude

    • Abstract: A solar-wind-driven empirical model of Pc3 wave activity at a mid-latitude location

      Annales Geophysicae, 33, 225-234, 2015

      Author(s): S. Lotz, B. Heilig, and P. Sutcliffe

      In this paper we describe the development of two empirical models of Pc3 wave activity observed at a ground station. The models are tasked to predict pulsation intensity at Tihany, Hungary, from the OMNI solar wind data set at 5 min time resolution. One model is based on artificial neural networks and the other on multiple linear regression. Input parameters to the models are iteratively selected from a larger set of candidate inputs. The optimal set of inputs are solar wind speed, interplanetary magnetic field orientation (via cone angle), proton density and solar zenith angle (representing local time). Solar wind measurements are shifted in time with respect to Pc3 data to account for the propagation time of ULF perturbations from upstream of the bow shock. Both models achieve correlation of about 70% between measured and predicted Pc3 wave intensity. The timescales at which the most important solar wind parameters influence pulsation intensity are calculated for the first time. We show that solar wind speed influences pulsation intensity at much longer timescales (about 2 days) than cone angle (about 1 h).
      PubDate: 2015-02-26T00:00:00+01:00
  • Relation between stratospheric sudden warming and the lunar effect on the
           equatorial electrojet based on Huancayo recordings

    • Abstract: Relation between stratospheric sudden warming and the lunar effect on the equatorial electrojet based on Huancayo recordings

      Annales Geophysicae, 33, 235-243, 2015

      Author(s): T. A. Siddiqui, H. Lühr, C. Stolle, and J. Park

      It has been known for many decades that the lunar tidal influence in the equatorial electrojet (EEJ) is noticeably enhanced during Northern Hemisphere winters. Recent literature has discussed the role of stratospheric sudden warming (SSW) events behind the enhancement of lunar tides and the findings suggest a positive correlation between the lunar tidal amplitude and lower stratospheric parameters (zonal mean air temperature and zonal mean zonal wind) during SSW events. The positive correlation raises the question whether an inverse approach could also be developed which makes it possible to deduce the occurrence of SSW events before their direct observations (before 1952) from the amplitude of the lunar tides. This study presents an analysis technique based on the phase of the semi-monthly lunar tide to determine the lunar tidal modulation of the EEJ. A statistical approach using the superposed epoch analysis is also carried out to formulate a relation between the EEJ tidal amplitude and lower stratospheric parameters. Using these results, we have estimated a threshold value for the tidal wave power that could be used to identify years with SSW events from magnetic field observations.
      PubDate: 2015-02-26T00:00:00+01:00
  • Auroral vortex street formed by the magnetosphere–ionosphere
           coupling instability

    • Abstract: Auroral vortex street formed by the magnetosphere–ionosphere coupling instability

      Annales Geophysicae, 33, 217-224, 2015

      Author(s): Y. Hiraki

      By performing three-dimensional magnetohydrodynamic simulations including Alfvén eigenmode perturbations most unstable to the ionospheric feedback effects, we examined the auroral vortex street that often appears just before substorm onset. We found that an initially placed arc splits, intensifies, and rapidly deforms into a vortex street. We also found that there is a critical convection electric field for growth of the Alfvén eigenmodes. The vortex street is shown to be a consequence of coupling between the magnetospheric Alfvén waves carrying field-aligned currents and the ionospheric density waves driven by Pedersen/Hall currents.
      PubDate: 2015-02-26T00:00:00+01:00
  • The influence of solar activity on action centres of atmospheric
           circulation in North Atlantic

    • Abstract: The influence of solar activity on action centres of atmospheric circulation in North Atlantic

      Annales Geophysicae, 33, 207-215, 2015

      Author(s): L. Sfîcă, M. Voiculescu, and R. Huth

      We analyse the response of sea level pressure and mid-tropospheric (500 hPa) geopotential heights to variations in solar activity. We concentrate on the Northern Hemisphere and North Atlantic in the period 1948–2012. Composite and correlation analyses point to a strengthening of the North Atlantic Oscillation and weakening (i.e. becoming more zonal) of the Pacific/North American pattern. The locations of points with lowest and highest sea level pressure in the North Atlantic change their positions between low and high solar activity.
      PubDate: 2015-02-26T00:00:00+01:00
  • The Hiccup: a dynamical coupling process during the autumn transition in
           the Northern Hemisphere – similarities and differences to sudden
           stratospheric warmings

    • Abstract: The Hiccup: a dynamical coupling process during the autumn transition in the Northern Hemisphere – similarities and differences to sudden stratospheric warmings

      Annales Geophysicae, 33, 199-206, 2015

      Author(s): V. Matthias, T. G. Shepherd, P. Hoffmann, and M. Rapp

      Sudden stratospheric warmings (SSWs) are the most prominent vertical coupling process in the middle atmosphere, which occur during winter and are caused by the interaction of planetary waves (PWs) with the zonal mean flow. Vertical coupling has also been identified during the equinox transitions, and is similarly associated with PWs. We argue that there is a characteristic aspect of the autumn transition in northern high latitudes, which we call the "hiccup", and which acts like a "mini SSW", i.e. like a small minor warming. We study the average characteristics of the hiccup based on a superimposed epoch analysis using a nudged version of the Canadian Middle Atmosphere Model, representing 30 years of historical data. Hiccups can be identified in about half the years studied. The mesospheric zonal wind results are compared to radar observations over Andenes (69° N, 16° E) for the years 2000–2013. A comparison of the average characteristics of hiccups and SSWs shows both similarities and differences between the two vertical coupling processes.
      PubDate: 2015-02-23T00:00:00+01:00
  • Corrigendum to "Development of the mesospheric Na layer at
           69&deg; N during the Geminids meteor shower 2010", published in
           Ann. Geophys., 31, 61–73, 2013

    • Abstract: Corrigendum to "Development of the mesospheric Na layer at 69° N during the Geminids meteor shower 2010", published in Ann. Geophys., 31, 61–73, 2013

      Annales Geophysicae, 33, 197-197, 2015

      Author(s): T. Dunker, U.-P. Hoppe, G. Stober, and M. Rapp

      No abstract available.
      PubDate: 2015-02-23T00:00:00+01:00
  • Tidal signatures of the thermospheric mass density and zonal wind at
           midlatitude: CHAMP and GRACE observations

    • Abstract: Tidal signatures of the thermospheric mass density and zonal wind at midlatitude: CHAMP and GRACE observations

      Annales Geophysicae, 33, 185-196, 2015

      Author(s): C. Xiong, Y.-L. Zhou, H. Lühr, and S.-Y. Ma

      By using the accelerometer measurements from CHAMP and GRACE satellites, the tidal signatures of the thermospheric mass density and zonal wind at midlatitudes have been analyzed in this study. The results show that the mass density and zonal wind at southern midlatitudes are dominated by a longitudinal wave-1 pattern. The most prominent tidal components in mass density and zonal wind are the diurnal tides D0 and DW2 and the semidiurnal tides SW1 and SW3. This is consistent with the tidal signatures in the F region electron density at midlatitudes as reported by Xiong and Lühr (2014). These same tidal components are observed both in the thermospheric and ionospheric quantities, supporting a mechanism that the non-migrating tides in the upper atmosphere are excited in situ by ion–neutral interactions at midlatitudes, consistent with the modeling results of Jones Jr. et al. (2013). We regard the thermospheric dynamics as the main driver for the electron density tidal structures. An example is the in-phase variation of D0 between electron density and mass density in both hemispheres. Further research including coupled atmospheric models is probably needed for explaining the similarities and differences between thermospheric and ionospheric tidal signals at midlatitudes.
      PubDate: 2015-02-04T00:00:00+01:00
  • Dual-spacecraft reconstruction of a three-dimensional magnetic flux rope
           at the Earth's magnetopause

    • Abstract: Dual-spacecraft reconstruction of a three-dimensional magnetic flux rope at the Earth's magnetopause

      Annales Geophysicae, 33, 169-184, 2015

      Author(s): H. Hasegawa, B. U. Ö. Sonnerup, S. Eriksson, T. K. M. Nakamura, and H. Kawano

      We present the first results of a data analysis method, developed by Sonnerup and Hasegawa (2011), for reconstructing three-dimensional (3-D), magnetohydrostatic structures from data taken as two closely spaced satellites traverse the structures. The method is applied to a magnetic flux transfer event (FTE), which was encountered on 27 June 2007 by at least three (TH-C, TH-D, and TH-E) of the five THEMIS probes near the subsolar magnetopause. The FTE was sandwiched between two oppositely directed reconnection jets under a southward interplanetary magnetic field condition, consistent with its generation by multiple X-line reconnection. The recovered 3-D field indicates that a magnetic flux rope with a diameter of ~ 3000 km was embedded in the magnetopause. The FTE flux rope had a significant 3-D structure, because the 3-D field reconstructed from the data from TH-C and TH-D (separated by ~ 390 km) better predicts magnetic field variations actually measured along the TH-E path than does the 2-D Grad–Shafranov reconstruction using the data from TH-C (which was closer to TH-E than TH-D and was at ~ 1250 km from TH-E). Such a 3-D nature suggests that the field lines reconnected at the two X-lines on both sides of the flux rope are entangled in a complicated way through their interaction with each other. The generation process of the observed 3-D flux rope is discussed on the basis of the reconstruction results and the pitch-angle distribution of electrons observed in and around the FTE.
      PubDate: 2015-02-03T00:00:00+01:00
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