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]
- Scintillation measurements at Bahir Dar during the high solar activity
phase of solar cycle 24
Abstract: Scintillation measurements at Bahir Dar during the high solar activity phase of solar cycle 24
Martin Kriegel, Norbert Jakowski, Jens Berdermann, Hiroatsu Sato, and Mogese Wassaie Mersha
Ann. Geophys., 35, 97-106, doi:10.5194/angeo-35-97-2017, 2017
Small-scale ionospheric disturbances may cause severe radio scintillations ofsignals transmitted from global navigation satellite systems (GNSSs).Consequently, small-scale plasma irregularities may heavily degrade theperformance of current GNSSs such as GPS, GLONASS or Galileo. This paperpresents analysis results obtained primarily from two high-rate GNSS receiverstations designed and operated by the German Aerospace Center (DLR) incooperation with Bahir Dar University (BDU) at 11.6° N,37.4° E. Both receivers collect raw data sampled at up to 50 Hz, fromwhich characteristic scintillation parameters such as the S4 index arededuced.
This paper gives a first overview of the measurement set-up and the observedscintillation events over Bahir Dar in 2015. Both stations are located closeto one another and aligned in an east–west, direction which allows us toestimate the zonal drift velocity and spatial dimension of equatorialionospheric plasma irregularities. Therefore, the lag times of movingelectron density irregularities and scintillation patterns are derived byapplying cross-correlation analysis to high-rate measurements of the slanttotal electron content (sTEC) along radio links between a GPS satellite andboth receivers and to the associated signal power,respectively. Finally, the drift velocity is derived from the estimated lagtime, taking into account the geometric constellation of both receivingantennas and the observed GPS satellites.
- Vertical wavenumber spectra of three-dimensional winds revealed by
radiosonde observations at midlatitude
Abstract: Vertical wavenumber spectra of three-dimensional winds revealed by radiosonde observations at midlatitude
Shao Dong Zhang, Chun Ming Huang, Kai Ming Huang, Ye Hui Zhang, Yun Gong, and Quan Gan
Ann. Geophys., 35, 107-116, doi:10.5194/angeo-35-107-2017, 2017
We present the first statistical results of vertical wind fluctuation spectra, which revealed a very shallow spectral structure, with mean slopes of −0.58 and −0.23 in the troposphere and lower stratosphere, respectively. No existing spectral theories can comprehensively explain the observed three-dimensional wind spectra, indicating that the spectral features of atmospheric fluctuations are far from fully understood.
- An improved troposphere tomographic approach considering the signals
coming from the side face of the tomographic area
Abstract: An improved troposphere tomographic approach considering the signals coming from the side face of the tomographic area
Qingzhi Zhao and Yibin Yao
Ann. Geophys., 35, 87-95, doi:10.5194/angeo-35-87-2017, 2017
A troposphere tomographic method has been proposed considering the signal rays penetrating from the side of the area of interest. Given the method above needs the establishment of a unit scale factor model using the radiosonde data at only one location in the research area, an improved approach is proposed by considering the reasonability of modelling data and the diversity of the modelling parameters for building a more accurate unit scale factor model.
- Ground-based acoustic parametric generator impact on the atmosphere and
ionosphere in an active experiment
Abstract: Ground-based acoustic parametric generator impact on the atmosphere and ionosphere in an active experiment
Yuriy G. Rapoport, Oleg K. Cheremnykh, Volodymyr V. Koshovy, Mykola O. Melnik, Oleh L. Ivantyshyn, Roman T. Nogach, Yuriy A. Selivanov, Vladimir V. Grimalsky, Valentyn P. Mezentsev, Larysa M. Karataeva, Vasyl. M. Ivchenko, Gennadi P. Milinevsky, Viktor N. Fedun, and Eugen N. Tkachenko
Ann. Geophys., 35, 53-70, doi:10.5194/angeo-35-53-2017, 2017
Before many catastrophic phenomena such as earthquakes, sound is generated at a very low frequency. It is already established that it can disturb the upper layer of the atmosphere – the ionosphere. Control of disasters' precursors is important. Using the unique, powerful sound generator, whose loudness is comparable to an ascending jet, we have constructed the theory and conducted a series of experiments trying to model acoustic action of disasters on the ionosphere.
- Absence of the strahl during times of slow wind
Abstract: Absence of the strahl during times of slow wind
Chris Gurgiolo and Melvyn L. Goldstein
Ann. Geophys., 35, 71-85, doi:10.5194/angeo-35-71-2017, 2017
Observations during periods when the solar wind has a speed
- Induction effects of geomagnetic disturbances in the geo-electric field
variations at low latitudes
Abstract: Induction effects of geomagnetic disturbances in the geo-electric field variations at low latitudes
Vafi Doumbia, Kouadio Boka, Nguessan Kouassi, Oswald Didier Franck Grodji, Christine Amory-Mazaudier, and Michel Menvielle
Ann. Geophys., 35, 39-51, doi:10.5194/angeo-35-39-2017, 2017
The electrical inductions within the Earth surface due to geomagnetic field variations were examined. For that purpose the records of the geomagnetic and geo-electric field variations observed in West Africa were used. We have found that the geomagnetic field brisk variations induce non-negligible geo-electric field variations at low latitudes. This result implies a possible intense geomagnetically induced current flow in the vicinity of the equatorial electrojet influence area.
- Signature of ionospheric irregularities under different geophysical
Abstract: Signature of ionospheric irregularities under different geophysical conditions on SBAS performance in the western African low-latitude region
Oladipo Emmanuel Abe, Xurxo Otero Villamide, Claudia Paparini, Rodrigue Herbert Ngaya, Sandro M. Radicella, and Bruno Nava
Ann. Geophys., 35, 1-9, doi:10.5194/angeo-35-1-2017, 2017
Rate of change of TEC (ROT) and its index (ROTI) are considered agood proxy to characterize the occurrence of ionospheric plasmairregularities like those observed after sunset at low latitudes. SBASs(satellite-based augmentation systems) are civil aviation systems thatprovide wide-area or regional improvement to single-frequency satellitenavigation using GNSS (Global Navigation Satellite System) constellations.Plasma irregularities in the path of the GNSS signal after sunset causesevere phase fluctuations and loss of locks of the signals in GNSS receiverat low-latitude regions. ROTI is used in this paper to characterize plasmadensity ionospheric irregularities in central–western Africa under nominaland disturbed conditions and identified some days of irregularityinhibition. A specific low-latitude algorithm is used to emulate potentialpossible SBAS message using real GNSS data in the western African low-latituderegion. The performance of a possible SBAS operation in the region underdifferent ionospheric conditions is analysed. These conditions includeeffects of geomagnetic disturbed periods when SBAS performance appears to beenhanced due to ionospheric irregularity inhibition. The results of thispaper could contribute to a feasibility assessment of a European Geostationary Navigation Overlay System-based SBAS inthe sub-Saharan African region.
- On the response of quasi-adiabatic particles to magnetotail
Abstract: On the response of quasi-adiabatic particles to magnetotail reconfigurations
Dominique C. Delcourt, Helmi V. Malova, and Lev M. Zelenyi
Ann. Geophys., 35, 11-23, doi:10.5194/angeo-35-11-2017, 2017
In a magnetic field reversal, the guiding center may not be valid due to large variation of the magnetic field on the length scale of the particle gyro-radius. Although they do not execute regular helical motion and temporarily meander inside the field reversal, quasi-adiabatic particles exit this reversal with a magnetic moment nearly identical to that at entry. We show that this behavior, which is a steady-state concept, can persist during dipolarization despite the induced electric field.
- Measurements of the total ozone column using a Brewer spectrophotometer
and TOMS and OMI satellite instruments over the Southern Space Observatory
Abstract: Measurements of the total ozone column using a Brewer spectrophotometer and TOMS and OMI satellite instruments over the Southern Space Observatory in Brazil
Lucas Vaz Peres, Hassan Bencherif, Nkanyiso Mbatha, André Passaglia Schuch, Abdoulwahab Mohamed Toihir, Nelson Bègue, Thierry Portafaix, Vagner Anabor, Damaris Kirsch Pinheiro, Neusa Maria Paes Leme, José Valentin Bageston, and Nelson Jorge Schuch
Ann. Geophys., 35, 25-37, doi:10.5194/angeo-35-25-2017, 2017
In this paper, we analyze the total ozone column over the Southern Space Observatory, Brazil, between 1992 and 2014 by Brewer spectrometer and TOMS and OMI satellite instruments, finding good agreement between the two. In addition, the seasonal TOC variation is dominated by an annual cycle, and the Quasi-Biennial Oscillation modulation was the main mode of interannual variability and in opposite phase to the total ozone column anomaly time series.
- The story of plumes: the development of a new conceptual framework for
understanding magnetosphere and ionosphere coupling
Abstract: The story of plumes: the development of a new conceptual framework for understanding magnetosphere and ionosphere coupling
Mark B. Moldwin, Shasha Zou, and Tom Heine
Ann. Geophys., 34, 1243-1253, doi:10.5194/angeo-34-1243-2016, 2016
A significant number of studies published over the last 15 years demonstrate that there is strong two-way coupling between the magnetosphere and ionosphere during geomagnetic activity; not only does the ionosphere respond to magnetospheric forcing during storms, but through its impact on wave generation, wave-particle interactions, ion outflow and mass loading at the dayside magnetopause and in the magnetotail, dense plasma plumes modulate the subsequent magnetospheric dynamics.
- Patches of polar mesospheric summer echoes characterized from radar
imaging observations with MAARSY
Abstract: Patches of polar mesospheric summer echoes characterized from radar imaging observations with MAARSY
Svenja Sommer and Jorge L. Chau
Ann. Geophys., 34, 1231-1241, doi:10.5194/angeo-34-1231-2016, 2016
Radar echoes from mesospheric altitudes (80–90 km) are called polar mesospheric summer echoes (PMSEs). These echoes can be used to derive wind velocities and turbulence strength estimations in a region where measurements are hard to perform. The small-scale structure of PMSEs has not been analysed before but, as we will show, has a major influence on wind and turbulence measurements. We also present a method to improve these measurements by using software beam-steering methods.
- Stability of solar correction for calculating ionospheric trends
Abstract: Stability of solar correction for calculating ionospheric trends
Jan Laštovička, Dalia Burešová, Daniel Kouba, and Peter Križan
Ann. Geophys., 34, 1191-1196, doi:10.5194/angeo-34-1191-2016, 2016
Global climate change affects the whole atmosphere, including the thermosphere and ionosphere. Calculations of long-term trends in the ionosphere are critically dependent on solar activity correction of ionospheric input data. The main result of this study is the finding that the solar activity correction used in calculating ionospheric long-term trends is not stable, as was assumed in all previous investigations of ionospheric trends.
- Spatial and temporal variations of wave energy in the nearshore waters of
the central west coast of India
Abstract: Spatial and temporal variations of wave energy in the nearshore waters of the central west coast of India
M. M. Amrutha and V. Sanil Kumar
Ann. Geophys., 34, 1197-1208, doi:10.5194/angeo-34-1197-2016, 2016
This study examines variation in wave power off the central west coast of India at water depths 30, 9 and 5 m based on buoy measured data. The study shows a significant reduction (~ 10–27 %) in wave power at 9 m depth compared to 30 m and the power at 5 m depth is 20–23 % less than that at 9 m. At 9 m water depth, the mean annual wave power is 6 kW m−1 and interannual variations up to 19.3 % are observed during 2009–2014; 75 % of the total annual wave energy is from this narrow directional sector.
- Derivation of turbulent energy dissipation rate with the Middle Atmosphere
Alomar Radar System (MAARSY) and radiosondes at Andøya, Norway
Abstract: Derivation of turbulent energy dissipation rate with the Middle Atmosphere Alomar Radar System (MAARSY) and radiosondes at Andøya, Norway
Qiang Li, Markus Rapp, Anne Schrön, Andreas Schneider, and Gunter Stober
Ann. Geophys., 34, 1209-1229, doi:10.5194/angeo-34-1209-2016, 2016
Turbulence is an essential process in the atmosphere and ocean. Clear-air turbulence is a well-known threat for the safety of aviation. Using a powerful MST radar, we detected turbulence and compared it with the results from radiosondes. The correlation between turbulence and background conditions, e.g., Richardson number and wind shears, is determined. There is a nearly negative correlation between turbulence and Richardson number independent of the length scale over which it was calculated.
- Observations of diffusion in the electron halo and strahl
Abstract: Observations of diffusion in the electron halo and strahl
Chris Gurgiolo and Melvyn L. Goldstein
Ann. Geophys., 34, 1175-1189, doi:10.5194/angeo-34-1175-2016, 2016
Using Cluster data we have noted observations of diffusion-like signatures in the energy range where the the solar wind halo and strahl populations overlap. This includes the development of a proto-halo. At present the source of this diffusion is not known or understood. The prime analysis was carried out through the use of phi–theta plots at individual energy steps. The motivation was to understand if repartitioning in energy was occurring at these locations.
- Euler potentials for two layers with non-constant current densities in the
ambient magnetic field aligned to the layers
Abstract: Euler potentials for two layers with non-constant current densities in the ambient magnetic field aligned to the layers
Marek Vandas and Eugene P. Romashets
Ann. Geophys., 34, 1165-1173, doi:10.5194/angeo-34-1165-2016, 2016
Magnetic field and motion of charged particles are examined near two parallel current sheets with non-uniformly distributed currents theoretically. Results can be applied to study of Birkeland currents which flow in the ionosphere along magnetic field lines and are connected to auroral phenomena.
- Spectral analysis of auroral geomagnetic activity during various solar
cycles between 1960 and 2014
Abstract: Spectral analysis of auroral geomagnetic activity during various solar cycles between 1960 and 2014
Pieter Benjamin Kotzé
Ann. Geophys., 34, 1159-1164, doi:10.5194/angeo-34-1159-2016, 2016
We use wavelets and Lomb–Scargle spectral analysis techniques to investigate the changing pattern of the different harmonics of the 27-day solar rotation period of the AE index during various phases of different solar cycles between 1960 and 2014. Results show that, particularly during the solar minimum of 23–24 in 2008, the 27-day period is no longer detectable above the 95 % CI, while auroral geomagnetic activity is now dominated by the second (13.5-day) and third (9.0-day) harmonics.
- Modeling anisotropic Maxwell–Jüttner distributions: derivation
Abstract: Modeling anisotropic Maxwell–Jüttner distributions: derivation and properties
Ann. Geophys., 34, 1145-1158, doi:10.5194/angeo-34-1145-2016, 2016
The paper develops a consistent model for the anisotropic Maxwell–Jüttner distribution. This is the velocity distribution in a gas of relativistic particles, where the temperature is not equi-distributed in all degrees of freedom. The physical requirements necessary for modeling this distribution are provided. The known models are examined showing that they do not fulfill these requirements, while a new model is constructed and studied that is consistent with all the required conditions.
- Decay times of transitionally dense specularly reflecting meteor trails
and potential chemical impact on trail lifetimes
Abstract: Decay times of transitionally dense specularly reflecting meteor trails and potential chemical impact on trail lifetimes
Wayne K. Hocking, Reynold E. Silber, John M. C. Plane, Wuhu Feng, and Marcial Garbanzo-Salas
Ann. Geophys., 34, 1119-1144, doi:10.5194/angeo-34-1119-2016, 2016
Meteoroids entering the atmosphere produce trails of ionized particles which can be detected with radar. The weakest ones are called underdense (the most common), the strongest are called overdense, and intermediate ones are transitional. Meteor radar signatures are used to determine atmospheric parameters like temperature and winds. We present new results which show the effect of ozone on the transitional trail lifetimes, which may eventually allow radar to measure mesospheric ozone.
- 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.