Annales Geophysicae (ANGEO)
[SJR: 1.176] [H-I: 63] [4 followers] Follow
Open Access journal
ISSN (Print) 0992-7689 - ISSN (Online) 1432-0576
Published by European Geosciences Union [8 journals]
- The solar activity dependence of nonmigrating tides in electron density
at low and middle latitudes observed by CHAMP and GRACE
Abstract: The solar activity dependence of nonmigrating tides in electron density at low and middle latitudes observed by CHAMP and GRACE
Yun-Liang Zhou, Li Wang, Chao Xiong, Hermann Lühr, and Shu-Ying Ma
Ann. Geophys., 34, 463-472, doi:10.5194/angeo-34-463-2016, 2016
The solar activity dependence of nonmigrating tides in electron density at low and middle latitudes observed by CHAMP and GRACE are investigated. The absolute amplitudes of DE3 at low latitudes as well as DE1, D0 and DW2 at middle latitudes are highly related to the solar activity, while their relative amplitudes show little dependence on the solar activity. A clear modulation by the QBO is found in the relative amplitudes of DE3 at low latitudes.
- Effect of data gaps: comparison of different spectral analysis methods
Abstract: Effect of data gaps: comparison of different spectral analysis methods
Costel Munteanu, Catalin Negrea, Marius Echim, and Kalevi Mursula
Ann. Geophys., 34, 437-449, doi:10.5194/angeo-34-437-2016, 2016
We investigate the effect of data gaps for various methods of estimating the amplitude spectrum of a time series. We probe the effects of a single data gap of varying size and of numerous small gaps distributed within the time series. We use synthetic data sets and magnetic field measurements from the Venus Express spacecraft. For multiple gaps and turbulent magnetic data, we show that some advanced methods overestimate the high frequencies, while FFT slightly underestimates them.
- An alternative way to identify local geomagnetically quiet days: a case
study using wavelet analysis
Abstract: An alternative way to identify local geomagnetically quiet days: a case study using wavelet analysis
Virginia Klausner, Andrés Reinaldo Rodriguez Papa, Cláudia Maria Nicole Cândido, Margarete Oliveira Domingues, and Odim Mendes
Ann. Geophys., 34, 451-462, doi:10.5194/angeo-34-451-2016, 2016
This paper proposes a new method to evaluate geomagnetic activity based on wavelet analysis during the solar minimum activity (2007). In order to accomplish this task, a newly developed algorithm called effectiveness wavelet coefficient (EWC) was applied. Furthermore, a comparison between the 5 geomagnetically quiet days determined by the Kp-based method and by wavelet-based method was performed. This paper provides a new insight since the geomagnetic activity indexes are mostly designed to quantify the extent of disturbance rather than the quietness. The results suggest that the EWC can be used as an alternative tool to accurately detect quiet days, and consequently, it can also be used as an alternative to determine the Sq baseline to the current Kp-based 5 quietest days method. Another important aspect of this paper is that most of the quietest local wavelet candidate days occurred in an interval 2 days prior to the high-speed-stream-driven storm events. In other words, the EWC algorithm may potentially be used to detect the quietest magnetic activity that tends to occur just before the arrival of high-speed-stream-driven storms.
- Modelling natural electromagnetic interference in man-made conductors
for space weather applications
Abstract: Modelling natural electromagnetic interference in man-made conductors for space weather applications
Ann. Geophys., 34, 427-436, doi:10.5194/angeo-34-427-2016, 2016
Power transmission lines above the ground, cables and pipelines, and, in general, all man-made long grounded conductors are exposed to the variations of natural electromagnetic field of wide frequency range. This interference often can compromise the systems operations. Paper offers frequency dependent approach in modelling the response of these systems to the geomagnetic variations. The formulas were proposed, analysed, verified and recommended for use in space weather applications.
- The influence of resistivity gradients on shock conditions for a Petschek
Abstract: The influence of resistivity gradients on shock conditions for a Petschek reconnection geometry
Christian Nabert and Karl-Heinz Glassmeier
Ann. Geophys., 34, 421-425, doi:10.5194/angeo-34-421-2016, 2016
Electrical resistivity can influence the occurrence of shock waves. We derive analytically necessary conditions for shocks in a nonuniform resistive magnetohydrodynamic plasma. The nonuniform resistivity significantly modifies the characteristic velocity of wave propagation. A sufficient gradient of the resistivity in a diffusion region can satisfy the necessary condition for the occurrence of slow shocks, which is related to Petschek reconnection.
- Statistical analysis of magnetotail fast flows and related magnetic
Abstract: Statistical analysis of magnetotail fast flows and related magnetic disturbances
Dennis Frühauff and Karl-Heinz Glassmeier
Ann. Geophys., 34, 399-409, doi:10.5194/angeo-34-399-2016, 2016
This study presents an investigation on the occurrence of fast flows in the magnetotail using the complete available data set of the THEMIS spacecraft for the years 2007 to 2015. First, basic statistical findings concerning velocity distributions, occurrence rates, group structures and key features of 16 000 events are presented using Superposed Epoch and Minimum Variance Analysis techniques.
- Latitudinal variability of the quasi-16-day wave in the middle
atmosphere over Brazilian stations
Abstract: Latitudinal variability of the quasi-16-day wave in the middle atmosphere over Brazilian stations
Amitava Guharay, Paulo Prado Batista, Barclay Robert Clemesha, Ricardo Arlen Buriti, and Nelson Jorge Schuch
Ann. Geophys., 34, 411-419, doi:10.5194/angeo-34-411-2016, 2016
A comparative study of the quasi-16-day wave in the middle from three Brazilian stations, indicates multiple modes of the concerned wave component. The wave amplitude shows maxima in summer and winter. A potential coupling of the concerned wave with other short period planetary waves is found. The dominant wave components vary from the westward to eastward from the tropical to mid-latitude in the stratosphere. The prevailing westerly wind may favor the wave filtering of westward waves.
- Wave–particle resonance condition test for ion-kinetic waves in the
Abstract: Wave–particle resonance condition test for ion-kinetic waves in the solar wind
Y. Narita, E. Marsch, C. Perschke, K.-H. Glassmeier, U. Motschmann, and H. Comişel
Ann. Geophys., 34, 393-398, doi:10.5194/angeo-34-393-2016, 2016
Conditions for the Landau and cyclotron resonances are tested for 543 waves (identified as local peaks in the energy spectra) in the magnetic field fluctuations of the solar wind measured by the Cluster spacecraft on a tetrahedral scale of 100 km. The resonance parameters are evaluated using the frequencies in the plasma rest frame, the parallel components of the wavevectors, the ion cyclotron frequency, and the ion thermal speed. The observed waves show a character of the sideband waves associated with the ion Bernstein mode, and are in a weak agreement with the fundamental electron cyclotron resonance in spite of the ion-kinetic scales. The electron cyclotron resonance is likely taking place in solar wind turbulence near 1 AU (astronomical unit).
- Equivalent currents associated with morning-sector geomagnetic
Pc5 pulsations during auroral substorms
Abstract: Equivalent currents associated with morning-sector geomagnetic Pc5 pulsations during auroral substorms
K. Kauristie, M. V. Uspensky, N. G. Kleimenova, O. V. Kozyreva, M. M. J. L. Van De Kamp, S. V. Dubyagin, and S. Massetti
Ann. Geophys., 34, 379-392, doi:10.5194/angeo-34-379-2016, 2016
This study presents some example events in which sudden changes in the auroral activity at midnight sector seem to have an impact on the intensity of morning-sector magnetic pulsations. Mechanisms which could link these two separate regions are discussed in the paper. Sudden changes in the solar wind properties and fast westward-propagating electrons are suggested to explain the coupling between midnight-sector and morning-sector phenomena.
- Measurement of momentum flux using two meteor radars in Indonesia
Abstract: Measurement of momentum flux using two meteor radars in Indonesia
Naoki Matsumoto, Atsuki Shinbori, Dennis M. Riggin, and Toshitaka Tsuda
Ann. Geophys., 34, 369-377, doi:10.5194/angeo-34-369-2016, 2016
We investigated the zonal and meridional momentum flux at 86–94 km using two nearly identical sets of meteor radar observation data at Koto Tabang and Biak in Indonesia (both at the Equator) by applying a method proposed by Hocking (2005). The observed zonal momentum flux at the two sites agreed reasonably well at 86, 90, and 94 km during the observation periods when the data acquisition rate was large enough. Our results suggest the usefulness of the Hocking method.
- Spatial dimensions of the electron diffusion region in anti-parallel
Abstract: Spatial dimensions of the electron diffusion region in anti-parallel magnetic reconnection
Takuma Nakamura, Rumi Nakamura, and Hiroshi Haseagwa
Ann. Geophys., 34, 357-367, doi:10.5194/angeo-34-357-2016, 2016
Magnetic reconnection is a key process in space and laboratory plasmas which transfers energies through the magnetic field topology change. The topology change in this process takes place in a small scale region called the electron diffusion region (EDR). In this paper, using high-resolution fully kinetic simulations, we successfully obtained the firm scaling laws of spatial dimensions of the EDR. The obtained scalings allow us to precisely predict observable dimensions of the EDR in real space.
- Three-model ensemble wind prediction in southern Italy
Abstract: Three-model ensemble wind prediction in southern Italy
Rosa Claudia Torcasio, Stefano Federico, Claudia Roberta Calidonna, Elenio Avolio, Oxana Drofa, Tony Christian Landi, Piero Malguzzi, Andrea Buzzi, and Paolo Bonasoni
Ann. Geophys., 34, 347-356, doi:10.5194/angeo-34-347-2016, 2016
Quality of wind prediction is of great importance since a good wind forecast allows the prediction of available wind power, improving the penetration of renewable energies into the energy market. This work shows the application of a technique to improve wind forecasting. The study area is southern Italy.
- Variations of Kelvin waves around the TTL region during the
stratospheric sudden warming events in the Northern Hemisphere winter
Abstract: Variations of Kelvin waves around the TTL region during the stratospheric sudden warming events in the Northern Hemisphere winter
Yue Jia, Shao Dong Zhang, Fan Yi, Chun Ming Huang, Kai Ming Huang, Yun Gong, and Quan Gan
Ann. Geophys., 34, 331-345, doi:10.5194/angeo-34-331-2016, 2016
Spatial and temporal variabilities of Kelvin waves during stratospheric sudden warming (SSW) events are investigated by the ERA-Interim reanalysis data, and the results are validated by the COSMIC temperature data. A case study on an exceptionally large SSW event in 2009, and a composite analysis comprising 18 events from 1980 to 2013 are presented. During SSW events, the average temperature increases by 20 K in the polar stratosphere, while the temperature in the tropical stratosphere decreases by about 4 K. Kelvin wave with wave numbers 1 and 2, and periods 10–20 days, clearly appear around the tropical tropopause layer (TTL) during SSWs. The Kelvin wave activity shows obvious coupling with the convection localized in the India Ocean and western Pacific (Indo-Pacific) region. Detailed analysis suggests that the enhanced meridional circulation driven by the extratropical planetary wave forcing during SSW events leads to tropical upwelling, which further produces temperature decrease in the tropical stratosphere. The tropical upwelling and cooling consequently result in enhancement of convection in the equatorial region, which excites the strong Kelvin wave activity. In addition, we investigated the Kelvin wave acceleration to the eastward zonal wind anomalies in the equatorial stratosphere during SSW events. The composite analysis shows that the proportion of Kelvin wave contribution ranges from 5 to 35 % during SSWs, much larger than in the non-SSW mid-winters (less than 5 % in the stratosphere). However, the Kelvin wave alone is insufficient to drive the equatorial eastward zonal wind anomalies during the SSW events, which suggests that the effects of other types of equatorial waves may not be neglected.
- Gravity-wave momentum fluxes in the mesosphere over Ascension Island
(8° S, 14° W) and the anomalous zonal winds of the
semi-annual oscillation in 2002
Abstract: Gravity-wave momentum fluxes in the mesosphere over Ascension Island (8° S, 14° W) and the anomalous zonal winds of the semi-annual oscillation in 2002
Andrew C. Moss, Corwin J. Wright, Robin N. Davis, and Nicholas J. Mitchell
Ann. Geophys., 34, 323-330, doi:10.5194/angeo-34-323-2016, 2016
Gravity waves are fundamental to the dynamics of the mesosphere. In some years very strong winds are observed in the first phase of the MSAO. It has been proposed that this is due to filtering of ascending gravity waves. We report the first gravity-wave momentum flux observations from the Ascension Island (8° S, 14° W) meteor radar and show that anomalous fluxes were observed during one such event in 2002. Analysis of the underlying winds suggests the wave-filtering hypothesis is not valid.
- Planar magnetic structures in coronal mass ejection-driven sheath regions
Abstract: Planar magnetic structures in coronal mass ejection-driven sheath regions
Erika Palmerio, Emilia K. J. Kilpua, and Neel P. Savani
Ann. Geophys., 34, 313-322, doi:10.5194/angeo-34-313-2016, 2016
Coronal Mass Ejections (CMEs) are giant clouds of plasma and magnetic field that erupt from the Sun and travel though the solar wind. They can cause interplanetary shocks in the vicinity of Earth. We show in our paper that the region that follows CME-driven shocks, known as sheath region, can obtain a planar configuration of the magnetic field lines (planar magnetic structure, PMS) due to the compression resulting from the shock itself or from the draping of the magnetic field ahead of the CME.
- A statistical study on the shape and position of the magnetotail
Abstract: A statistical study on the shape and position of the magnetotail neutral sheet
Sudong Xiao, Tielong Zhang, Yasong Ge, Guoqiang Wang, Wolfgang Baumjohann, and Rumi Nakamura
Ann. Geophys., 34, 303-311, doi:10.5194/angeo-34-303-2016, 2016
We study the average shape and position of the magnetotail neutral sheet based on magnetic field data obtained by Cluster, Geotail, TC-1, and THEMIS from the years 1995 to 2013. All data in the aberrated GSM (geocentric solar magnetospheric) coordinate system are normalized to the same solar wind pressure 2 nPa and downtail distance X ∼ −20RE. Our results show characteristics of the neutral sheet, as follows. (1) The neutral sheet assumes a greater degree of curve in the YZ cross section when the dipole tilt increases, the Earth dipole tilt angle affects the neutral sheet configuration not only in the YZ cross section but also in the XY cross section, and the neutral sheet assumes a more significant degree of tilt in the XY cross section when the dipole tilt increases. (2) Counterclockwise twisting of the neutral sheet with 3.10° is observed, looking along the downtail direction, for the positive interplanetary magnetic field (IMF) BY with a value of 3 to 8 nT, and clockwise twisting of the neutral sheet with 3.37° for the negative IMF BY with a value of −8 to −3 nT, and a northward IMF can result in a greater twisting of the near-tail neutral sheet than southward. The above results can be a reference to the neutral sheet model. Our large database also shows that the displaced ellipse model is effective to study the average shape of the neutral sheet with proper parameters when the dipole tilt angle is larger (less) than 10° (−10° ).
- Periodic waves in the lower thermosphere observed by OI630 nm
Abstract: Periodic waves in the lower thermosphere observed by OI630 nm airglow images
I. Paulino, A. F. Medeiros, S. L. Vadas, C. M. Wrasse, H. Takahashi, R. A. Buriti, D. Leite, S. Filgueira, J. V. Bageston, J. H. A. Sobral, and D. Gobbi
Ann. Geophys., 34, 293-301, doi:10.5194/angeo-34-293-2016, 2016
Periodic waves have been observed over São João do Cariri during almost one solar cycle. Similarities between the characteristics of these events with observations at other places around the world were noted, primarily the spectral parameters. Most observed waves have appeared during magnetically quiet nights, and the occurrence of those waves followed the solar activity. Due to their characteristics, most of them must have had different generation mechanisms from the Perkins instability.
- Atmospheric CO2 source and sink patterns over the
Abstract: Atmospheric CO2 source and sink patterns over the Indian region
Suvarna Fadnavis, K. Ravi Kumar, Yogesh K. Tiwari, and Luca Pozzoli
Ann. Geophys., 34, 279-291, doi:10.5194/angeo-34-279-2016, 2016
Analysis of 10 years (2000–2009) of Carbon Tracker (CT-2010) model CO2 fluxes gives insights into the regional variation of CO2 fluxes over the Indian land mass. CO2 emission hot spots overlap with locations of densely clustered thermal power plants, coal mines, and other industrial and urban centres. CO2 sink regions coincide with locations of dense forests with less industrial centres. CO2 fossil fuel emissions show good agreement with two bottom-up inventories REAS v1.11 and EDGAR v4.2.
- Assessment of BeiDou differential code bias variations from
multi-GNSS network observations
Abstract: Assessment of BeiDou differential code bias variations from multi-GNSS network observations
S. G. Jin, R. Jin, and D. Li
Ann. Geophys., 34, 259-269, doi:10.5194/angeo-34-259-2016, 2016
The differential code bias (DCB) is one of main errors for high-precision GNSS TEC estimation and positioning applications. In this paper, daily DCBs of the BeiDou System (BDS) are estimated and investigated from multi-GNSS network observations (2013–2014), which are compared with GPS results. The DCB of BDS satellites is a little less stable than GPS results, especially for GEO satellites. Zero-mean condition effects are not the dominant factor for the higher RMS of BDS satellite DCB.
- Interpretation of deformed ionograms induced by vertical ground motion
of seismic Rayleigh waves and infrasound in the thermosphere
Abstract: Interpretation of deformed ionograms induced by vertical ground motion of seismic Rayleigh waves and infrasound in the thermosphere
Takashi Maruyama, Kamil Yusupov, and Adel Akchurin
Ann. Geophys., 34, 271-278, doi:10.5194/angeo-34-271-2016, 2016
A significant anomaly was observed in the ionogram at Kazan, Russia, following the 2010 M8.8 Chile earthquake, which was caused by vertical ground motions of Rayleigh waves and the resulting acoustic waves propagating upward. The anomaly was characterized by steep satellite traces for which the range increased rapidly with frequency. The inclined ionospheric density perturbation caused oblique returns of sounding radio waves in addition to the nearly vertical returns of the main trace.