Annales Geophysicae (ANGEO)
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Open Access journal
ISSN (Print) 0992-7689 - ISSN (Online) 1432-0576
Published by European Geosciences Union [8 journals]
- Spatial and temporal variation of total electron content as revealed by
principal component analysis
Abstract: Spatial and temporal variation of total electron content as revealed by principal component analysis
Elsayed R. Talaat and Xun Zhu
Ann. Geophys., 34, 1109-1117, doi:10.5194/angeo-34-1109-2016, 2016
Global total electron content data derived from the assimilated thermosphere–ionosphere model are analyzed using empirical orthogonal function (EOF) decomposition and the principal component analysis technique. The spectral analysis of the time series of the EOF coefficients reveals how different mechanisms such as solar flux variation, change in the orbital declination, nonlinear mode coupling and geomagnetic activity are separated and expressed in different EOFs.
- Deduction of the rates of radial diffusion of protons from the structure
of the Earth's radiation belts
Abstract: Deduction of the rates of radial diffusion of protons from the structure of the Earth's radiation belts
Alexander S. Kovtyukh
Ann. Geophys., 34, 1085-1098, doi:10.5194/angeo-34-1085-2016, 2016
From the data on the protons of the Earth’s radiation belts, the rate of radial diffusion of these particles is directly calculated. This is done by solving the systems of equations which describe the balance of radial transport/acceleration and ionization losses of protons. These results are very consistent with the radial diffusion of particles under the influence of the electric field pulsations in the range of the drift frequencies of the protons around Earth.
- Mirror mode waves in Venus's magnetosheath: solar minimum vs. solar
Abstract: Mirror mode waves in Venus's magnetosheath: solar minimum vs. solar maximum
Martin Volwerk, Daniel Schmid, Bruce T. Tsurutani, Magda Delva, Ferdinand Plaschke, Yasuhito Narita, Tielong Zhang, and Karl-Heinz Glassmeier
Ann. Geophys., 34, 1099-1108, doi:10.5194/angeo-34-1099-2016, 2016
The behaviour of mirror mode waves in Venus's magnetosheath is investigated for solar minimum and maximum conditions. It is shown that the total observational rate of these waves does not change much; however, the distribution over the magnetosheath is significantly different, as well as the growth and decay of the waves during these different solar activity conditions.
- Identification of the different magnetic field contributions during a
geomagnetic storm in magnetospheric and ground observations
Abstract: Identification of the different magnetic field contributions during a geomagnetic storm in magnetospheric and ground observations
Tommaso Alberti, Mirko Piersanti, Antonio Vecchio, Paola De Michelis, Fabio Lepreti, Vincenzo Carbone, and Leonardo Primavera
Ann. Geophys., 34, 1069-1084, doi:10.5194/angeo-34-1069-2016, 2016
We investigate the time variation of the magnetospheric and Earth's magnetic field during both quiet and disturbed periods. We identify the timescale variations associated with different magnetospheric current systems, solar-wind–magnetosphere high-frequency interactions, ionospheric processes, and internal dynamics of the magnetosphere. In addition, we propose a new local index for the identification of the intensity of a geomagnetic storm on the ground.
- Latitudinal and longitudinal dependence of the cosmic ray diurnal
anisotropy during 2001–2014
Abstract: Latitudinal and longitudinal dependence of the cosmic ray diurnal anisotropy during 2001–2014
Anastasia Tezari, Helen Mavromichalaki, Dimitrios Katsinis, Anastasios Kanellakopoulos, Sofia Kolovi, Christina Plainaki, and Maria Andriopoulou
Ann. Geophys., 34, 1053-1068, doi:10.5194/angeo-34-1053-2016, 2016
The diurnal anisotropy of cosmic ray intensity for the timeperiod 2001 to 2014 is studied, covering the maximum and the descending phaseof solar cycle 23, the minimum between solar cycles 23 and 24, and theascending phase and maximum of solar cycle 24. Cosmic ray intensitydata from 11 neutron monitor stations located at different places around theNorthern Hemisphere obtained from the high-resolution Neutron MonitorDatabase (NMDB) were used. Special software was developed for the calculationsof the amplitude and the phase of the diurnal anisotropy vectors on annualand monthly basis using Fourier analysis and for the creation of the harmonicdial diagrams. The geomagnetic bending for each station was taken intoaccount in our calculations determined from the asymptotic cones of eachstation via the Tsyganenko96 (Tsyganenko and Stern, 1996) magnetospheric model. From our analysis, it wasresulted that there is a different behavior of the diurnal anisotropy vectorsduring the different phases of the solar cycles depending on the solarmagnetic field polarity. The latitudinal and longitudinal distribution of thecosmic ray diurnal anisotropy was also examined by grouping the stationsaccording to their geographic coordinates, and it was shown that diurnalvariation is modulated not only by the latitude but also by the longitude ofthe stations. The diurnal anisotropy during strong events of solar and/orcosmic ray activity is discussed.
- Analysis of aerosol absorption properties and transport over North Africa
and the Middle East using AERONET data
Abstract: Analysis of aerosol absorption properties and transport over North Africa and the Middle East using AERONET data
Ashraf Farahat, Hesham El-Askary, Peter Adetokunbo, and Abu-Tharr Fuad
Ann. Geophys., 34, 1031-1044, doi:10.5194/angeo-34-1031-2016, 2016
The Middle East capitals are subjected to numerous dust storms along with local emissions and/or those transported from biomass burning or industrial activities. A combination of these aerosols results in poor air quality and poses significant health hazards. We investigated the transport of aerosols and their impact on the air quality using different parameters derived from the AERONET ground observations.
- GPS network observation of traveling ionospheric disturbances following
the Chelyabinsk meteorite blast
Abstract: GPS network observation of traveling ionospheric disturbances following the Chelyabinsk meteorite blast
Feng Ding, Tian Mao, Lianhuan Hu, Baiqi Ning, Weixing Wan, and Yungang Wang
Ann. Geophys., 34, 1045-1051, doi:10.5194/angeo-34-1045-2016, 2016
Two traveling ionospheric disturbances (TIDs) were observed by the GPS network in Asia following the large meteorite blast over Chelyabinsk, Russia. No TIDs propagating in a global range were found. Features of TIDs were compared with those excited by early nuclear explosion tests. It is inferred from our analysis that the energy release of the Chelyabinsk meteorite blast may not be large enough to excite such ionospheric disturbances in a global range as some nuclear explosions have done.
- Plasma fluctuations at the flanks of the Earth's magnetosheath at ion
Abstract: Plasma fluctuations at the flanks of the Earth's magnetosheath at ion kinetic scales
Liudmila Rakhmanova, Maria Riazantseva, and Georgy Zastenker
Ann. Geophys., 34, 1011-1018, doi:10.5194/angeo-34-1011-2016, 2016
We present a statistical study of the magnetosheath plasma fluctuationspectra at a high-frequency range (with frequencies from 0.01 to 10 Hz).Variations of ion flux value and its direction are considered. The directionof ion flux is characterized by a polar angle – the deviation of the ionflux vector from the Sun–Earth line. We consider 290 Fourier's spectra thatcan be described by two power laws with a break, i.e., a change of slope. Theion flux fluctuation spectra are shown to have breaks at higher frequenciescompared to the polar angle spectra. We compare the frequency of the breakwith the gyrostructure frequency for a number of cases. We show the polarangle break frequency to usually be smaller than the gyrostructure frequency.The dependencies of spectrum parameters such as the slopes and the breakfrequency on plasma parameters are also considered.
- Electrodynamic influence on the diurnal behaviour of neutral daytime
Abstract: Electrodynamic influence on the diurnal behaviour of neutral daytime airglow emissions
Deepak K. Karan, Duggirala Pallamraju, Kedar A. Phadke, Tatiparti Vijayalakshmi, Tarun K. Pant, and Shyamoli Mukherjee
Ann. Geophys., 34, 1019-1030, doi:10.5194/angeo-34-1019-2016, 2016
Dayglow emission variability is expected to show a symmetric solar zenith-angle-dependent diurnal pattern as the production mechanisms are dominated by solar flux; however, this is not always the case. Our investigation reveals an imprint of equatorial electrodynamics on the neutral dayglow emission variability, as opposed to that of the solar zenith angle. This has implications in gaining a comprehensive understanding of the coupled nature of the ion-neutral behaviour in the upper atmosphere.
- Ionospheric tomography by gradient-enhanced kriging with STEC measurements
and ionosonde characteristics
Abstract: Ionospheric tomography by gradient-enhanced kriging with STEC measurements and ionosonde characteristics
David Minkwitz, Karl Gerald van den Boogaart, Tatjana Gerzen, Mainul Hoque, and Manuel Hernández-Pajares
Ann. Geophys., 34, 999-1010, doi:10.5194/angeo-34-999-2016, 2016
We extend the kriging of the ionospheric electron density with slant total electron content (STEC) measurements based on a spatial covariance to kriging with a spatial–temporal covariance and develop a novel tomography approach by gradient-enhanced kriging assimilating STEC and F2 layer characteristics. The methods are cross-validated with independent measurements and point out the potential compensation for the often observed bias in the estimation of the F2 layer peak height.
- Multipoint spacecraft observations of long-lasting poloidal Pc4 pulsations
in the dayside magnetosphere on 1–2 May 2014
Abstract: Multipoint spacecraft observations of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere on 1–2 May 2014
Galina Korotova, David Sibeck, Mark Engebretson, John Wygant, Scott Thaller, Harlan Spence, Craig Kletzing, Vassilis Angelopoulos, and Robert Redmon
Ann. Geophys., 34, 985-998, doi:10.5194/angeo-34-985-2016, 2016
We use magnetic field and plasma observations from the Van Allen Probes,Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Geostationary Operational Environmental Satellite system (GOES) spacecraft to study the spatial and temporal characteristicsof long-lasting poloidal Pc4 pulsations in the dayside magnetosphere. Thepulsations were observed after the main phase of a moderate storm during lowgeomagnetic activity. The pulsations occurred during various interplanetaryconditions and the solar wind parameters do not seem to control theoccurrence of the pulsations. The most striking feature of the Pc4 magneticfield pulsations was their occurrence at similar locations during three offour successive orbits. We used this information to study the latitudinalnodal structure of the pulsations and demonstrated that the latitudinalextent of the magnetic field pulsations did not exceed 2 Earth radii(RE). A phase shift between the azimuthal and radial components of theelectric and magnetic fields was observed from ZSM = 0.30 RE to ZSM = −0.16 RE. We used magnetic and electric field data from Van AllenProbes to determine the structure of ULF waves. We showed that the Pc4magnetic field pulsations were radially polarized and are the second-mode harmonic waves. We suggest that the spacecraft were near a magnetic fieldnull during the second orbit when they failed to observe the magnetic fieldpulsations at the local times where pulsations were observed on previous andsuccessive orbits. We investigated the spectral structure of the Pc4pulsations. Each spacecraft observed a decrease of the dominant period as itmoved to a smaller L shell (stronger magnetic field strength). We demonstratedthat higher frequencies occurred at times and locations where Alfvénvelocities were greater, i.e., on Orbit 1. There is some evidence that theperiods of the pulsations increased during the plasmasphere refillingfollowing the storm.
- On the role of ion-scale whistler waves in space and astrophysical plasma
Abstract: On the role of ion-scale whistler waves in space and astrophysical plasma turbulence
Horia Comişel, Yasuhiro Nariyuki, Yasuhito Narita, and Uwe Motschmann
Ann. Geophys., 34, 975-984, doi:10.5194/angeo-34-975-2016, 2016
Competition of linear mode waves is studied numerically tounderstand the energy cascade mechanism in plasma turbulence on ion-kineticscales. Hybrid plasma simulations are performed in a 3-D simulationbox by pumping large-scale Alfvén waves on the fluid scale. The result iscompared with that from our earlier 2-D simulations. We find that thewhistler mode is persistently present both in the 2-D and 3-Dsimulations irrespective of the initial setup, e.g., the amplitude of theinitial pumping waves, while all the other modes are excited and damped suchthat the energy is efficiently transported to thermal energy overnon-whistler mode. The simulation results suggest that the whistler modecould transfer the fluctuation energy smoothly from the fluid scale down tothe electron-kinetic scale, and justifies the notion of whistlerturbulence.
- Seasonal variations and north–south asymmetries in polar wind outflow
due to solar illumination
Abstract: Seasonal variations and north–south asymmetries in polar wind outflow due to solar illumination
Lukas Maes, Romain Maggiolo, and Johan De Keyser
Ann. Geophys., 34, 961-974, doi:10.5194/angeo-34-961-2016, 2016
Ion outflow from the ionospheric regions at the highest latitudes is mainly driven by solar illumination. It is an important factor affecting atmospheric escape and space weather. But this region rotates into and out of the sunlight on a daily and seasonal basis. This creates daily and seasonal variations in the outflow, even with both hemispheres combined. The north–south asymmetry in Earth's magnetic field causes extra variations and asymmetries. This was studied with a simple empirical model.
- Evidence for transient, local ion foreshocks caused by dayside
Abstract: Evidence for transient, local ion foreshocks caused by dayside magnetopause reconnection
Yann Pfau-Kempf, Heli Hietala, Steve E. Milan, Liisa Juusola, Sanni Hoilijoki, Urs Ganse, Sebastian von Alfthan, and Minna Palmroth
Ann. Geophys., 34, 943-959, doi:10.5194/angeo-34-943-2016, 2016
We have simulated the interaction of the solar wind – the charged particles and magnetic fields emitted by the Sun into space – with the magnetic field of the Earth. The solar wind flows supersonically and creates a shock when it encounters the obstacle formed by the geomagnetic field. We have identified a new chain of events which causes phenomena in the downstream region to eventually cause perturbations at the shock and even upstream. This is confirmed by ground and satellite observations.
- Observational evidence for new instabilities in the midlatitude E and F
Abstract: Observational evidence for new instabilities in the midlatitude E and F region
David L. Hysell, Miguel Larsen, and Michael Sulzer
Ann. Geophys., 34, 927-941, doi:10.5194/angeo-34-927-2016, 2016
Radar observations of the E- and F-region ionosphere from the Arecibo Observatory made during moderately disturbed conditions are presented. Plasma irregularities in both ionospheric regions were observed. We investigate the role of neutral atmospheric dynamics and instabilities in causing the ionospheric disturbances. A number of viable instability mechanisms rooted in neutral dynamics are identified.
- Proton and heavy ion acceleration by stochastic fluctuations in the
Abstract: Proton and heavy ion acceleration by stochastic fluctuations in the Earth's magnetotail
Filomena Catapano, Gaetano Zimbardo, Silvia Perri, Antonella Greco, and Anton V. Artemyev
Ann. Geophys., 34, 917-926, doi:10.5194/angeo-34-917-2016, 2016
Spacecraft observations show that energetic ions are found in the Earth’s magnetotail, with energies ranging from tens of keV to a few hundreds of keV. In this paper we carry out test particle simulations in which protons and other ion species are injected in the Vlasov magnetic field configurations obtained by Catapano et al. (2015). Three-dimensional time-dependent stochastic electromagnetic perturbations are included in the simulation box, so that the ion acceleration process is studied.
- Filamentary field-aligned currents at the polar cap region
during northward interplanetary magnetic field derived with the
Abstract: Filamentary field-aligned currents at the polar cap region duringnorthward interplanetary magnetic field derived with the Swarmconstellation
Hermann Lühr, Tao Huang, Simon Wing, Guram Kervalishvili, Jan Rauberg, and Haje Korth
Ann. Geophys., 34, 901-915, doi:10.5194/angeo-34-901-2016, 2016
ESA's constellation mission Swarm makes it possible for the first time to determine field-aligned currents (FACs) reliably in the ionosphere. FACs are able to transport energy from the solar wind to the Earth and heat the upper atmosphere. Here we investigate FAC structures that have been missed by previous satellite missions. Most of them are found poleward of the northern light zone. The energy sources seem to be located on the nightside of Earth about 100 000 km away.
- Can the comprehensive model phase 4 (CM4) predict the geomagnetic diurnal
field for days away from quiet time?
Abstract: Can the comprehensive model phase 4 (CM4) predict the geomagnetic diurnal field for days away from quiet time?
Ann. Geophys., 34, 887-900, doi:10.5194/angeo-34-887-2016, 2016
We assess the CM4 of daily variation and whether it can be applied to times and activity levels outside of those that provide input data for the model. Our conclusion shows that the model works well at times outside those from which CM4 was produced and also performs better than expected at activity levels higher than that for which CM4 was designed, although it fails to predict short-period behaviour.
- Influence of Indian summer monsoon variability on the surface waves in
the coastal regions of eastern Arabian Sea
Abstract: Influence of Indian summer monsoon variability on the surface waves in thecoastal regions of eastern Arabian Sea
V. Sanil Kumar and Jesbin George
Ann. Geophys., 34, 871-885, doi:10.5194/angeo-34-871-2016, 2016
Influence of monsoon variability on the surface waves using measured data covering 7 years and reanalysis data from 1979 to 2015 during the Indian summer monsoon in the eastern Arabian Sea is examined. A high positive correlation (r ~ 0.84) between average low-level jet for the block 0–15° N, 50–75° E and wave height of eastern Arabian Sea is observed in all months except August. The monsoon seasonal average wave height is found to be relatively low during the strong El Niño years.
- Large-scale coordinated observations of Pc5 pulsation
Abstract: Large-scale coordinated observations of Pc5 pulsationevents
Zolile Mtumela, Anthony D. M. Walker, Judy A. E. Stephenson, and Michael J. Kosch
Ann. Geophys., 34, 857-870, doi:10.5194/angeo-34-857-2016, 2016
Pc5 pulsations are global magnetohydrodynamic events in the magnetosphere. This article details the analysis of Pc5 pulsation events observed by SuperDARN high-frequency radars within their field of view together with magnetometers. We believe that despite much theoretical knowledge, very few pulsation events observed by multiple radars have been reported in the literature to determine in detail the physical characteristics of Pc5 pulsation events by direct observation.