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  Subjects -> PHYSICS (Total: 767 journals)
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    - MECHANICS (20 journals)
    - NUCLEAR PHYSICS (44 journals)
    - OPTICS (91 journals)
    - PHYSICS (557 journals)
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PHYSICS (557 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: 38)
Advanced Materials     Hybrid Journal   (Followers: 400)
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: 4)
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: 8)
Advances in Synchrotron Radiation     Hybrid Journal   (Followers: 1)
AIP Advances     Open Access   (Followers: 6)
AIP Conference Proceedings     Full-text available via subscription   (Followers: 2)
American Journal of Applied Sciences     Open Access   (Followers: 31)
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: 2)
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: 9)
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)
ASTRA Proceedings     Open Access  
Astronomy & Geophysics     Hybrid Journal   (Followers: 1)
Astrophysical Journal Letters     Full-text available via subscription   (Followers: 3)
Atoms     Open Access  
Attention, Perception & Psychophysics     Full-text available via subscription   (Followers: 7)
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 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: 53)
Composites Part B : Engineering     Hybrid Journal   (Followers: 72)
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: 16)
Current Applied Physics     Full-text available via subscription   (Followers: 4)
Diamond and Related Materials     Hybrid Journal   (Followers: 12)

        1 2 3 4 5 6 | Last

Journal Cover   Annales Geophysicae (ANGEO)
  [SJR: 1.151]   [H-I: 57]   [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]
  • 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° 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
       
  • Inter-annual variations in wave spectral characteristics at a location off
           the central west coast of India

    • Abstract: Inter-annual variations in wave spectral characteristics at a location off the central west coast of India

      Annales Geophysicae, 33, 159-167, 2015

      Author(s): V. Sanil Kumar and M. Anjali Nair

      The inter-annual variations in wave spectrum are examined based on the wave data measured at 9 m water depth off the central west coast of India from 2009 to 2012 using a wave rider buoy. The temporal variation of the spectral energy density over a calendar year indicates similar variation in all the four years studied. The inter-annual variations in wave spectrum are observed in all months with larger variations during January to February, May and October to November due to the changes in wind-sea. The seasonal average wave spectrum during the monsoon (June–September) is single-peaked and the swell component is high in 2011 compared to other years. The annual averaged wave spectrum had higher peak energy during 2011 due to the higher spectral energy present during the monsoon period. During the non-monsoon period, two peaks are predominantly observed in the wave spectra; with the average peak at 0.07 Hz corresponding to the swells from the Indian Ocean and another at 0.17 Hz due to the local wind field.
      PubDate: 2015-02-03T00:00:00+01:00
       
  • Statistical study of the night-time F-layer dynamics at the magnetic
           equator in West Africa during the solar minimum period 1995–1997

    • Abstract: Statistical study of the night-time F-layer dynamics at the magnetic equator in West Africa during the solar minimum period 1995–1997

      Annales Geophysicae, 33, 143-157, 2015

      Author(s): K. S. Tanoh, B. J.-P. Adohi, I. S. Coulibaly, C. Amory-Mazaudier, A. T. Kobea, and P. Assamoi

      In this paper, we report on the night-time equatorial F-layer height behaviour at Korhogo (9.2° N, 5° W; 2.4° S dip lat), Ivory Coast, in the West African sector during the solar minimum period 1995–1997. The data were collected from quarter-hourly ionograms of an Ionospheric Prediction Service (IPS) 42-type vertical sounder. The main focus of this work was to study the seasonal changes in the F-layer height and to clarify the equinox transition process recently evidenced at Korhogo during 1995, the year of declining solar flux activity. The F-layer height was found to vary strongly with time, with up to three main phases. The night-to-night variability of these morphological phases was then analysed. The early post-sunset slow rise, commonly associated with rapid chemical recombination processes in the bottom part of the F layer, remained featureless and was observed regardless of the date. By contrast, the following event, either presented like the post-sunset height peak associated with the evening E × B drift, or was delayed to the midnight sector, thus involving another mechanism. The statistical analysis of the occurrence of these events throughout the solar minimum period 1995–1997 revealed two main F-layer height patterns, each characteristic of a specific season. The one with the post-sunset height peak was associated with the northern winter period, whereas the other, with the midnight height peak, characterized the northern summer period. The transition process from one pattern to the other took place during the equinox periods and was found to last only a few weeks. We discuss these results in the light of earlier works.
      PubDate: 2015-01-30T00:00:00+01:00
       
  • Traveling ionospheric disturbances triggered by the 2009 North Korean
           underground nuclear explosion

    • Abstract: Traveling ionospheric disturbances triggered by the 2009 North Korean underground nuclear explosion

      Annales Geophysicae, 33, 137-142, 2015

      Author(s): X. Zhang and L. Tang

      Underground nuclear explosions (UNEs) can induce acoustic-gravity waves, which disturb the ionosphere and initiate traveling ionospheric disturbances (TIDs). In this paper, we employ a multi-step and multi-order numerical difference method with dual-frequency GPS data to detect ionospheric disturbances triggered by the North Korean UNE on 25 May 2009. Several International GNSS Service (IGS) stations with different distances (400 to 1200 km) from the epicenter were chosen for the experiment. The results show that there are two types of disturbances in the ionospheric disturbance series: high-frequency TIDs with periods of approximately 1 to 2 min and low-frequency waves with period spectrums of 2 to 5 min. The observed TIDs are situated around the epicenter of the UNE, and show similar features, indicating the origin of the observed disturbances is the UNE event. According to the amplitudes, periods and average propagation velocities, the high-frequency and low-frequency TIDs can be attributed to the acoustic waves in the lower ionosphere and higher ionosphere, respectively.
      PubDate: 2015-01-30T00:00:00+01:00
       
  • Pc2-3 geomagnetic pulsations on the ground, in the ionosphere, and in the
           magnetosphere: MM100, CHAMP, and THEMIS observations

    • Abstract: Pc2-3 geomagnetic pulsations on the ground, in the ionosphere, and in the magnetosphere: MM100, CHAMP, and THEMIS observations

      Annales Geophysicae, 33, 117-128, 2015

      Author(s): N. Yagova, B. Heilig, and E. Fedorov

      We analyze Pc2-3 pulsations recorded by the CHAMP (CHAllenging Minisatellite Payload) satellite in the F layer of the Earth's ionosphere, on the ground, and in the magnetosphere during quiet geomagnetic conditions. The spectra of Pc2-3 pulsations recorded in the F layer are enriched with frequencies above 50 mHz in comparison to the ground Pc2-3 spectra. These frequencies are higher than the fundamental harmonics of the field line resonances in the magnetosphere. High quality signals with dominant frequencies 70–200 mHz are a regular phenomenon in the F layer and in the magnetosphere. The mean latitude of the maximum Pc2-3 occurrence rate lies at L ≈ 3.5 in the F layer, i.e., inside the plasmasphere. Day-to-day variations of the L value of the CHAMP Pc2-3 occurrence rate maximum follow the plasmapause day-to-day variations. Polarization and amplitude of Pc2-3s in the magnetosphere, in the ionosphere, and on the ground allow us to suggest that they are generated as fast magnetosonic (FMS) waves in the outer magnetosphere and are partly converted into shear Alfven waves near the plasmapause. The observed ground-to-ionosphere amplitude ratio during the night is interpreted as a result of the Alfven wave transmission through the ionosphere. The problem of wave transmission through the ionosphere is solved theoretically by means of a numerical solution of the full-wave equation for the Alfven wave reflection from and transmission through a horizontally stratified ionosphere. The best agreement between the calculated and measured values of the ground-to-ionosphere amplitude ratio is found for k = 5 × 10−3 km−1, i.e., the observed ground-to-ionosphere amplitude ratio corresponds to a wave spatial scale which could provide a Doppler shift within a few percent of the apparent frequency of the Pc2-3 pulsations as recorded by a low-orbiting spacecraft.
      PubDate: 2015-01-28T00:00:00+01:00
       
  • Three-dimensional morphology of equatorial plasma bubbles deduced from
           measurements onboard CHAMP

    • Abstract: Three-dimensional morphology of equatorial plasma bubbles deduced from measurements onboard CHAMP

      Annales Geophysicae, 33, 129-135, 2015

      Author(s): J. Park, H. Lühr, and M. Noja

      Total electron content (TEC) between Low-Earth-Orbit (LEO) satellites and the Global Navigation Satellite System (GNSS) satellites can be used to constrain the three-dimensional morphology of equatorial plasma bubbles (EPBs). In this study we investigate TEC measured onboard the Challenging Minisatellite Payload (CHAMP) from 2001 to 2005. We only use TEC data obtained when CHAMP passed through EPBs: that is, when in situ plasma density measurements at CHAMP altitude also show EPB signatures. The observed TEC gradient along the CHAMP track is strongest when the corresponding GNSS satellite is located equatorward and westward of CHAMP with elevation angles of about 40–60°. These elevation and azimuth angles are in agreement with the angles expected from the morphology of the plasma depletion shell proposed by Kil et al.(2009).
      PubDate: 2015-01-28T00:00:00+01:00
       
  • A dominant acoustic-gravity mode in the polar thermosphere

    • Abstract: A dominant acoustic-gravity mode in the polar thermosphere

      Annales Geophysicae, 33, 101-108, 2015

      Author(s): A. K. Fedorenko, A. V. Bespalova, O. K. Cheremnykh, and E. I. Kryuchkov

      The article presents a summary of the main findings of the systematic study of acoustic-gravity waves (AGWs) in the polar thermosphere. This study was based on the in situ measurements made by the Dynamics Explorer 2 (DE2) spacecraft late in its mission when it descended low enough (250–400 km). It was found out that AGWs in the polar thermosphere are observed within a narrow frequency band close to the Brunt–Väisälä frequency and with horizontal wavelengths about 500–600 km. The broadband spectrum of travelling ionospheric disturbance (TID) frequencies observed by radars is caused by the Doppler effect. The AGW amplitudes do not depend on the altitude, but grow almost linearly with the wind velocity. They propagate towards the wind.
      PubDate: 2015-01-27T00:00:00+01:00
       
  • The extreme solar storm of May 1921: observations and a complex
           topological model

    • Abstract: The extreme solar storm of May 1921: observations and a complex topological model

      Annales Geophysicae, 33, 109-116, 2015

      Author(s): H. Lundstedt, T. Persson, and V. Andersson

      A complex solid torus model was developed in order to be able to study an extreme solar storm, the so-called "Great Storm" or "New York Railroad Storm" of May 1921, when neither high spatial and time resolution magnetic field measurements, solar flare nor coronal mass ejection observations were available. We suggest that a topological change happened in connection with the occurrence of the extreme solar storm. The solar storm caused one of the most severe space weather effects ever.
      PubDate: 2015-01-27T00:00:00+01:00
       
  • Observations and modeling of UHF-band scintillation occurrence probability
           over the low-latitude region of China during the maximum activity of solar
           cycle 24

    • Abstract: Observations and modeling of UHF-band scintillation occurrence probability over the low-latitude region of China during the maximum activity of solar cycle 24

      Annales Geophysicae, 33, 93-100, 2015

      Author(s): H. Zhang, Y. Liu, J. Wu, T. Xu, and D. Sheng

      The climatological characteristics of UHF-band scintillations over the low-latitude region of China were investigated by analyzing the observations recorded at three stations of our regional network of satellite-beacon-based scintillation monitoring in 2013. The three stations are Hainan (geographic 20.0° N, 110.3° E; geomagnetic 10.1° N, 177.4° W, dip 28.2°), Guangzhou (geographic 23.0° N, 113.0° E; geomagnetic 13.1° N, 174.8° W, dip 33.9°) and Kunming (geographic 25.6° N, 103.7° E; geomagnetic 15.7° N, 176.4° E, dip 39.0°), located at low latitudes of China. The variations of UHF-band scintillation occurrence with latitude, time and season are presented in detail to understand the morphology and climatology of ionospheric scintillations over the low-latitude region of China. An equinoctial asymmetry in the occurrences of scintillation and an obvious difference of the onset time of scintillations between Hainan and Kunming is noted in this data set. Subsequently, the ionosonde data are utilized to study the possible causes of the asymmetry between two equinoxes. The observations suggest that the mean critical frequency (foF2) at 20:00 LT (12:00 UT) in the autumnal equinoctial months (September and October) and the vernal equinoctial months (March and April) has a similar asymmetry. The ratio of the mean foF2 between two equinoxes is proportional to the ratio between the maximum scintillation occurrence in the autumnal equinox and in the vernal equinox. Therefore, this ratio can act as a proxy for the equinoctial asymmetry in the occurrences of scintillation over the low-latitude region of China, and can be used to model the equinoctial asymmetry in our empirical climatological model of scintillation occurrence probability (CMSOP). The CMSOP can provide the predictions of the occurrences of scintillation over the low-latitude region of China and was validated in this study.
      PubDate: 2015-01-16T00:00:00+01:00
       
  • Dipolarization fronts in the near-Earth space and substorm dynamics

    • Abstract: Dipolarization fronts in the near-Earth space and substorm dynamics

      Annales Geophysicae, 33, 63-74, 2015

      Author(s): I. I. Vogiatzis, A. Isavnin, Q.-G. Zong, E. T. Sarris, S. W. Lu, and A. M. Tian

      During magnetospheric substorms and plasma transport in the Earth's magnetotail various magnetic structures can be detected. Dipolarization fronts and flux ropes are the most prominent structures characteristic for substorm dynamics. However, they are treated as separate magnetotail features independent of each other. In this paper, we analyze a number of dipolarization fronts observed by the THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft at different geocentric distances by applying the magnetohydrostatic Grad–Shafranov (GS) reconstruction technique. Our analysis shows that there is a possibility of dipolarization fronts to originate from highly dissipated flux ropes which are in the late stage of their evolution, subjected to a continuous magnetic deterioration due to the reconnection process. These results may improve our understanding of magnetoplasma processes in Earth's magnetotail.
      PubDate: 2015-01-15T00:00:00+01:00
       
  • Radiation dose of aircrews during a solar proton event without
           ground-level enhancement

    • Abstract: Radiation dose of aircrews during a solar proton event without ground-level enhancement

      Annales Geophysicae, 33, 75-78, 2015

      Author(s): R. Kataoka, Y. Nakagawa, and T. Sato

      A significant enhancement of radiation doses is expected for aircrews during ground-level enhancement (GLE) events, while the possible radiation hazard remains an open question during non-GLE solar energetic particle (SEP) events. Using a new air-shower simulation driven by the proton flux data obtained from GOES satellites, we show the possibility of significant enhancement of the effective dose rate of up to 4.5 μSv h−1 at a conventional flight altitude of 12 km during the largest SEP event that did not cause a GLE. As a result, a new GOES-driven model is proposed to give an estimate of the contribution from the isotropic component of the radiation dose in the stratosphere during non-GLE SEP events.
      PubDate: 2015-01-15T00:00:00+01:00
       
  • Experimental test of the ρ(1-α) evolution for rotational
           discontinuities: cluster magnetopause observations

    • Abstract: Experimental test of the ρ(1-α) evolution for rotational discontinuities: cluster magnetopause observations

      Annales Geophysicae, 33, 79-91, 2015

      Author(s): A. Blagau, G. Paschmann, B. Klecker, and O. Marghitu

      Rotational discontinuities (RDs) are governed by two relations: the Walén relation predicting that the plasma velocity observed in the deHoffmann–Teller frame equals the local Alfvén velocity and another relation that connects the variation in plasma mass density, ρ, to variations in the pressure anisotropy factor, α, defined as α: ≡(p∥ − p⊥) μ0/B2, so that ρ(1 − α) is constant. While the Walén relation has become a standard tool for classifying magnetopause crossings as RDs , the ρ(1 − α)= const. condition has never been directly verified at the same time, largely due to problems with determining ρ when no ion composition measurements were available. In fact, to overcome the lack of composition information, the validity of the relation has often been assumed and the Walén relation reformulated so that variations in ρ are replaced by variations in α. In this paper we exploit the availability of high-time-resolution composition measurements on the Cluster spacecraft to directly test the ρ (1− α)= const. condition for three magnetopause crossings, identified as RDs from the application of the Walén relation to measurements of plasma ions and magnetic field by the CIS (Cluster Ion Spectrometry) and FGM (flux-gate magnetometer) instruments, respectively. We find that the relation is not fulfilled in either case. In one event, with a fairly large content of oxygen ions, the Walén test improved when the contribution from these ions was taken into account. Through comparisons of the measured ion densities with simultaneously measured total electron densities by the Waves of HIgh frequency and Sounder for Probing of Electron density by Relaxation (WHISPER) instrument, we were able to exclude the possibility that ion populations hidden to the CIS instrument because of their very low energies could have changed ρ to match the ρ(1 − α)= const. condition. We also excluded the possibility that energetic ions above the CIS energy range could have sufficiently changed the true α. It thus appears that the ρ(1 − α)= const. condition, for reasons not presently understood, is not valid for the kind of RD-like structures we observe.
      PubDate: 2015-01-15T00:00:00+01:00
       
  • Validation of GPS atmospheric water vapor with WVR data in satellite
           tracking mode

    • Abstract: Validation of GPS atmospheric water vapor with WVR data in satellite tracking mode

      Annales Geophysicae, 33, 55-61, 2015

      Author(s): M. Shangguan, S. Heise, M. Bender, G. Dick, M. Ramatschi, and J. Wickert

      Slant-integrated water vapor (SIWV) data derived from GPS STDs (slant total delays), which provide the spatial information on tropospheric water vapor, have a high potential for assimilation to weather models or for nowcasting or reconstruction of the 3-D humidity field with tomographic techniques. Therefore, the accuracy of GPS STD is important, and independent observations are needed to estimate the quality of GPS STD. In 2012 the GFZ (German Research Centre for Geosciences) started to operate a microwave radiometer in the vicinity of the Potsdam GPS station. The water vapor content along the line of sight between a ground station and a GPS satellite can be derived from GPS data and directly measured by a water vapor radiometer (WVR) at the same time. In this study we present the validation results of SIWV observed by a ground-based GPS receiver and a WVR. The validation covers 184 days of data with dry and wet humidity conditions. SIWV data from GPS and WVR generally show good agreement with a mean bias of −0.4 kg m−2 and an rms (root mean square) of 3.15 kg m−2. The differences in SIWV show an elevation dependent on an rms of 7.13 kg m−2 below 15° but of 1.76 kg m−2 above 15°. Nevertheless, this elevation dependence is not observed regarding relative deviations. The relation between the differences and possible influencing factors (elevation angles, pressure, temperature and relative humidity) are analyzed in this study. Besides the elevation, dependencies between the atmospheric humidity conditions, temperature and the differences in SIWV are found.
      PubDate: 2015-01-13T00:00:00+01:00
       
  • Three-dimensional multi-fluid model of a coronal streamer belt with a
           tilted magnetic dipole

    • Abstract: Three-dimensional multi-fluid model of a coronal streamer belt with a tilted magnetic dipole

      Annales Geophysicae, 33, 47-53, 2015

      Author(s): L. Ofman, E. Provornikova, L. Abbo, and S. Giordano

      Observations of streamers in extreme ultraviolet (EUV) emission with SOHO/UVCS show dramatic differences in line profiles and latitudinal variations in heavy ion emission compared to hydrogen Ly-α emission. In order to use ion emission observations of streamers as the diagnostics of the slow solar wind properties, an adequate model of a streamer including heavy ions is required. We extended a previous 2.5-D multi-species magnetohydrodynamics (MHD) model of a coronal streamer to 3-D spherical geometry, and in the first approach we consider a tilted dipole configuration of the solar magnetic field. The aim of the present study is to test the 3-D results by comparing to previous 2.5-D model result for a 3-D case with moderate departure from azimuthal symmetry. The model includes O5+ ions with preferential empirical heating and allows for calculation of their density, velocity and temperature in coronal streamers. We present the first results of our 3-D multi-fluid model showing the parameters of protons, electrons and heavy ions (O5+) at the steady-state solar corona with a tilted steamer belt. We find that the 3-D results are in qualitative agreement with our previous 2.5-D model, and show longitudinal variation in the variables in accordance with the tilted streamer belt structure. Properties of heavy coronal ions obtained from the 3-D model together with EUV spectroscopic observations of streamers will help understanding the 3-D structures of streamers reducing line-of-sight integration ambiguities and identifying the sources of the slow solar wind in the lower corona. This leads to improved understanding of the physics of the slow solar wind.
      PubDate: 2015-01-12T00:00:00+01:00
       
  • The nightside magnetic field line open–closed boundary and polar
           rain electron energy-latitude dispersion

    • Abstract: The nightside magnetic field line open–closed boundary and polar rain electron energy-latitude dispersion

      Annales Geophysicae, 33, 39-46, 2015

      Author(s): S. Wing and Y. L. Zhang

      The polar rain electrons near the open–closed field line boundary on the nightside often exhibit energy-latitude dispersion, in which the energy decreases with decreasing latitude. The solar wind electrons from the last open-field line would E × B drift equatorward as they move toward the ionosphere, resulting in the observed dispersion. This process is modeled successfully by an open-field line particle precipitation model. The existing method for determining the magnetotail X line distance from the electron dispersion underestimates the electron path length from the X line to the ionosphere by at least 33%. The best estimate of the path length comes from using the two highest energy electrons in the dispersion region. The magnetic field line open–closed boundary is located poleward of the highest energy electrons in the dispersion region, which in turn is located poleward of Defense Meteorological Satellite Program (DMSP) b6, b5e, and b5i boundaries. In the four events examined, b6 is located at least 0.7–1.5° equatorward of the magnetic field line open–closed boundary. The energy-latitude dispersion seen in the electron overhang may result from the plasma sheet electron curvature and gradient drifts into the newly closed field line.
      PubDate: 2015-01-12T00:00:00+01:00
       
  • Spectrum analysis of short-period K index behaviour at
           high and mid-latitudes

    • Abstract: Spectrum analysis of short-period K index behaviour at high and mid-latitudes

      Annales Geophysicae, 33, 31-37, 2015

      Author(s): P. B. Kotzé

      Geomagnetic activity levels during the declining phase and solar minimum period of the solar cycle are considerably different from those during the solar maximum phase. Previous studies revealed variations in the pattern of recurrent activity from cycle to cycle as well as variations in the average geomagnetic activity levels during a solar cycle. During the declining phase of a solar cycle (and solar minimum), the solar and interplanetary causes of geomagnetic activity are substantially different from those during the solar maximum phase. Co-rotating fast solar wind streams originating from large polar coronal holes, extending towards the Sun's equator, interact with the Earth's magnetosphere, resulting in recurrent geomagnetic activity particularly during solar cycle minimum periods. This is a well-known phenomenon with respect to 27.0- and 13.5-day recurrence geomagnetic activity, and it is well-known to be related to sectorial (non-axial) poloidal magnetic field structure in the Sun. Published results of the recent solar-cycle-23 minimum showed that the presence of 9.0- and 6.7-day recurrent geomagnetic activities can be attributed to the sectorial spherical harmonic structure present in the solar magnetic field. In this study we performed a wavelet and Lomb–Scargle analysis of the geomagnetic activity K index at Lerwick (LER), Hermanus (HER) and Canberra (CNB) for the period between 1960 and 2010, overlapping with solar cycles 20 to 23. Daily mean K indices are used to identify how several harmonics of the 27.0-day recurrent period change during each solar cycle when comparing high and mid-latitude geomagnetic activity, applying a 95% confidence level. In particular the behaviour of the second (13.5-day), third (9.0-day) and fourth (6.7-day) harmonics are investigated by doing a wavelet analysis of each individual year's K indices at each location. Results obtained show that particularly during solar minima the 27.0-day period is no longer detectable above the 95% confidence level, and that geomagnetic activity is in fact dominated by higher harmonics like 13.5-, 9.0- and 6.7-day periods. These findings in fact are in line with previous investigations and confirm the results obtained by researchers using other geomagnetic activity indices like \textit{aa} and C9. The wavelet-spectrum analysis also reveals that during the downward phase of cycle 23 and the very long minimum of 23–24 between 2002 and 2008, the 27.0-day activity period drops below the 95% confidence level. This is confirmed by Lomb–Scargle analyses of every year's K index activity. Results obtained in this study support evidence by other investigations that this can be attributed to the lack of coronal-mass ejection (CME)-dominated solar activity during solar minima, periods characterized by strong solar dipolar magnetic fields, less sunspot numbers than at solar maxima, and multiple prominent co-rotating solar wind streams present. This analysis further confirms previous studies by other authors that the pattern of recurrent activity is dictated by the configuration of coronal holes which give rise to related high-speed streams during a solar cycle by analysing K indices at both high- and mid-latitude magnetic observatories.
      PubDate: 2015-01-09T00:00:00+01:00
       
  • Physics of outflows near solar active regions

    • Abstract: Physics of outflows near solar active regions

      Annales Geophysicae, 33, 25-29, 2015

      Author(s): D. J. Price and Y. Taroyan

      Hinode/EIS observations have revealed outflows near active regions which remain unexplained. An outflow region observed by the EUV Imaging Spectrometer (EIS) that appears slightly redshifted at low temperatures and blueshifted at higher temperatures is presented. We conduct simulations and use those to create synthetic line profiles in order to replicate the observed line profiles of an apparent open structure. The results of the forward modelling support a scenario whereby long loops consisting of multiple strands undergo a cyclical process of heating and cooling on timescales of approximately 80 min.
      PubDate: 2015-01-07T00:00:00+01:00
       
 
 
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