Magnetic field-aligned plasma currents in gravitational fields
Summary: Currents due to slow bulk electron motion along vertical magnetic fields are studied for plasmas subject to a gravitational force. 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. The alternative is that only time-varying solutions exist.
O. E. Garcia, E. Leer, H. L. Pécseli, and J. K. Trulsen Ann. Geophys., 33, 257-266, doi:10.5194/angeo-33-257-2015, 2015 AbstractFull Article (PDF, 280 KB)
03 Mar 2015
Azimuthal velocity shear within an Earthward fast flow – further evidence for magnetotail untwisting?
Summary: An azimuthal velocity shear with a reversal within an earthward magnetotail fast flow is studied using Cluster observations. In addition, ionospheric SuperDARN data and different magnetospheric models (T96 and TF04) are utilized when interpreting the Cluster observations. Untwisting of twisted tail B field lines is a good candidate to explain the observations.
T. Pitkänen, M. Hamrin, P. Norqvist, T. Karlsson, H. Nilsson, A. Kullen, S. M. Imber, and S. E. Milan Ann. Geophys., 33, 245-255, doi:10.5194/angeo-33-245-2015, 2015 AbstractFull Article (PDF, 1116 KB)Special Issue
03 Mar 2015
Relation between stratospheric sudden warming and the lunar effect on the equatorial electrojet based on Huancayo recordings
Summary: This paper presents the long-term observations of lunar tidal signatures in the equatorial electrojet (EEJ) and their relation to stratospheric sudden warming (SSW) events. We propose an approach to estimate the occurrence of SSW events before their direct observations (before 1952) from the magnetic field observations at Huancayo.
T. A. Siddiqui, H. Lühr, C. Stolle, and J. Park Ann. Geophys., 33, 235-243, doi:10.5194/angeo-33-235-2015, 2015 AbstractFull Article (PDF, 338 KB)
26 Feb 2015
A solar-wind-driven empirical model of Pc3 wave activity at a mid-latitude location
Summary: This paper describes the development of empirical models that are capable of predicting Pc3 pulsation intensity from solar wind parameters (e.g. plasma flow speed, proton density, and interplanetary magnetic field (IMF) orientation). We also calculate the typical timescales at which different solar wind parameters influence the excitation of these waves: solar wind speed influences pulsation intensity at much longer timescales (about 2 days) than IMF orientation (about 1 hour).
S. Lotz, B. Heilig, and P. Sutcliffe Ann. Geophys., 33, 225-234, doi:10.5194/angeo-33-225-2015, 2015 AbstractFull Article (PDF, 323 KB)
26 Feb 2015
Auroral vortex street formed by the magnetosphere–ionosphere coupling instability
Summary: By performing 3-D MHD simulations including Alfven 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. The vortex street is shown to be a consequence of M-I coupling between field-aligned currents and Pedersen/Hall currents.
The influence of solar activity on action centres of atmospheric circulation in North Atlantic
Summary: A possible link between solar activity and the atmospheric pressure fields is investigated using NCEP/NCAR data at ground level and at 500hPa, in the Northern Hemisphere for the cold season, with a focus on the North Atlantic centres of action. The Icelandic low seems to be most sensitive to the solar signal by moving towards north and by confining its activity area during months with high solar activity.
L. Sfîcă, M. Voiculescu, and R. Huth Ann. Geophys., 33, 207-215, doi:10.5194/angeo-33-207-2015, 2015 AbstractFull Article (PDF, 1591 KB)
26 Feb 2015
The Hiccup: a dynamical coupling process during the autumn transition in the Northern Hemisphere – similarities and differences to sudden stratospheric warmings
Summary: A vertical coupling process in the northern high-latitude middle atmosphere has been identified during the equinox transitions, which we call the “hiccup” and which acts like a “mini sudden stratospheric warming (SSW)”. We study the average characteristics of the hiccup based on a composite analysis using a nudged model. A comparison of the average characteristics of hiccups and SSWs shows both similarities and differences between the two vertical coupling processes.
V. Matthias, T. G. Shepherd, P. Hoffmann, and M. Rapp Ann. Geophys., 33, 199-206, doi:10.5194/angeo-33-199-2015, 2015 AbstractFull Article (PDF, 2401 KB)
23 Feb 2015
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
Tidal signatures of the thermospheric mass density and zonal wind at midlatitude: CHAMP and GRACE observations
C. Xiong, Y.-L. Zhou, H. Lühr, and S.-Y. Ma Ann. Geophys., 33, 185-196, doi:10.5194/angeo-33-185-2015, 2015 AbstractFull Article (PDF, 354 KB)
04 Feb 2015
Dual-spacecraft reconstruction of a three-dimensional magnetic flux rope at the Earth's magnetopause
Summary: A novel data analysis technique for recovering three-dimensional (3-D) magnetic field structures from in situ measurements by two satellites is applied for the first time to a magnetic flux rope observed by the THEMIS spacecraft near the Earth's subsolar magnetopause. We found that the flux rope resulting from multiple X-line reconnection was significantly 3-D and consisted of the field lines with different topologies, suggesting a complex interaction of the solar wind and the magnetosphere.
H. Hasegawa, B. U. Ö. Sonnerup, S. Eriksson, T. K. M. Nakamura, and H. Kawano Ann. Geophys., 33, 169-184, doi:10.5194/angeo-33-169-2015, 2015 AbstractFull Article (PDF, 1194 KB)Supplement (32114 KB)
03 Feb 2015
Inter-annual variations in wave spectral characteristics at a location off the central west coast of India
Summary: Inter-annual variations in wave spectrum are examined at 9m water depth from 2009 to 2012 based on measured data. Variations in the wave spectrum are observed inter-annually from January to February, May and October to November due to the changes in wind sea. Average wave spectrum during the monsoon is single peaked; during non-monsoon period, two peaks are observed. Due to sea breeze an increase in spectral energy of the wind-sea part is observed between 15 and 18 UTC from February to April.
V. Sanil Kumar and M. Anjali Nair Ann. Geophys., 33, 159-167, doi:10.5194/angeo-33-159-2015, 2015 AbstractFull Article (PDF, 7491 KB)
03 Feb 2015
Statistical study of the night-time F-layer dynamics at the magnetic equator in West Africa during the solar minimum period 1995–1997
K. S. Tanoh, B. J.-P. Adohi, I. S. Coulibaly, C. Amory-Mazaudier, A. T. Kobea, and P. Assamoi Ann. Geophys., 33, 143-157, doi:10.5194/angeo-33-143-2015, 2015 AbstractFull Article (PDF, 613 KB)
30 Jan 2015
Traveling ionospheric disturbances triggered by the 2009 North Korean underground nuclear explosion
X. Zhang and L. Tang Ann. Geophys., 33, 137-142, doi:10.5194/angeo-33-137-2015, 2015 AbstractFull Article (PDF, 194 KB)
30 Jan 2015
Three-dimensional morphology of equatorial plasma bubbles deduced from measurements onboard CHAMP
Summary: Total electron content (TEC) between low-Earth-orbit (LEO) satellites and the Global Navigation Satellite System (GNSS) satellites can be used to constrain three-dimensional morphology of equatorial plasma bubbles (EPBs). TEC gradient observed along the LEO track is strongest when the corresponding GNSS satellite is located equatorward and westward of the LEO satellite. This anisotropy supports the idea that EPBs have three-dimensional shell structures.
J. Park, H. Lühr, and M. Noja Ann. Geophys., 33, 129-135, doi:10.5194/angeo-33-129-2015, 2015 AbstractFull Article (PDF, 1504 KB)
28 Jan 2015
Pc2-3 geomagnetic pulsations on the ground, in the ionosphere, and in the magnetosphere: MM100, CHAMP, and THEMIS observations
N. Yagova, B. Heilig, and E. Fedorov Ann. Geophys., 33, 117-128, doi:10.5194/angeo-33-117-2015, 2015 AbstractFull Article (PDF, 255 KB)
28 Jan 2015
The extreme solar storm of May 1921: observations and a complex topological model
H. Lundstedt, T. Persson, and V. Andersson Ann. Geophys., 33, 109-116, doi:10.5194/angeo-33-109-2015, 2015 AbstractFull Article (PDF, 3228 KB)
27 Jan 2015
A dominant acoustic-gravity mode in the polar thermosphere
Summary: 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 spacecraft. It was found out that AGWs in the polar thermosphere are observed within a narrow frequency band and with horizontal wavelengths about 500-600km. The connection between the directions of motion of AGW and polar wind circulation was detected.
A. K. Fedorenko, A. V. Bespalova, O. K. Cheremnykh, and E. I. Kryuchkov Ann. Geophys., 33, 101-108, doi:10.5194/angeo-33-101-2015, 2015 AbstractFull Article (PDF, 510 KB)Special Issue
27 Jan 2015
Observations and modeling of UHF-band scintillation occurrence probability over the low-latitude region of China during the maximum activity of solar cycle 24
Summary: Variations of UHF-band scintillation occurrence with latitude, time and season over the low-latitude region of China are presented. The ratio of the mean foF2 at 20:00LT between two equinoxes, which could act as a proxy of the equinoctial asymmetry in the occurrences of scintillation, is proportional to the ratio between the maximum scintillation occurrence in the autumn equinox and in the vernal equinox. The empirical climatological model of scintillation occurrence probability was validated.
H. Zhang, Y. Liu, J. Wu, T. Xu, and D. Sheng Ann. Geophys., 33, 93-100, doi:10.5194/angeo-33-93-2015, 2015 AbstractFull Article (PDF, 151 KB)
16 Jan 2015
Experimental test of the ρ(1-α) evolution for rotational discontinuities: cluster magnetopause observations
Summary: Rotational discontinuities (RDs) in plasma allow a magnetic connection between different plasma regimes. One of their defining relations describes a balance between changes in plasma mass density and pressure anisotropy. The paper uses the high-time-resolution data from the Cluster satellites to directly test that relation at the terrestrial magnetopause, when standard analysis predicts that this boundary behaves like an RD. The experimental evidence shows that the said relation is not fulfilled
A. Blagau, G. Paschmann, B. Klecker, and O. Marghitu Ann. Geophys., 33, 79-91, doi:10.5194/angeo-33-79-2015, 2015 AbstractFull Article (PDF, 9628 KB)
15 Jan 2015
Radiation dose of aircrews during a solar proton event without ground-level enhancement
Summary: 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/hr at a conventional flight altitude of 12 km during the largest solar proton event that did not cause a ground-level enhancement. 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.
R. Kataoka, Y. Nakagawa, and T. Sato Ann. Geophys., 33, 75-78, doi:10.5194/angeo-33-75-2015, 2015 AbstractFull Article (PDF, 82 KB)