scholarly journals Regular daily variations in satellite magnetic total intensity data

2007 ◽  
Vol 25 (10) ◽  
pp. 2167-2174 ◽  
Author(s):  
J. P. R. Turner ◽  
D. E. Winch ◽  
D. J. Ivers ◽  
R. J. Stening
Keyword(s):  
Local Time ◽  
Field Measurements ◽  
Mean Value ◽  
Low Earth Orbit ◽  
Magnetic Data ◽  
Spherical Harmonic Analysis ◽  
Quiet Time ◽  
Champ Satellite ◽  
Daily Variations ◽  
Low Earth Orbit Satellites

Abstract. Regular magnetic daily quiet time (Sq) variations in total intensity of about 30 nT amplitude are determined in Universal Time (UT) from satellite magnetic field measurements. The CHAMP satellite traverses all hours of local time in 132 days and the Sq variations in total intensity are therefore calculated as an average over the 132 days for each hour of UT. Results are compared with the Sq daily variations in total intensity for the region above the ionosphere calculated from Malin's (1973) spherical harmonic analysis of the Sq Fourier coefficients for hourly mean value magnetic data from a global distribution of ground-based magnetic observatories. From the reasonable agreement between the two calculations, we conclude that low-Earth orbit satellites that traverse all hours of local time can determine Sq variations in total intensity above the ionosphere.

scholarly journals Magnetospheric contributions to geomagnetic daily variations

1996 ◽  
Vol 14 (5) ◽  
pp. 538-544 ◽  
Author(s):  
N. Olsen
Keyword(s):  
Harmonic Analysis ◽  
Local Time ◽  
Spherical Harmonic ◽  
Spherical Harmonic Analysis ◽  
Average Value ◽  
Daily Variations ◽  
Non Local ◽  
Current Systems

Abstract. The contribution of magnetospheric current systems to geomagnetic daily variations is analyzed by means of a spherical harmonic analysis (SHA) using elementary models as well as the Tsyganenko model of the magnetosphere. It is discovered that the magnetospheric contribution to some SHA coefficients is much higher than the known average value of about 20%, especially when considering non-local time terms and solstitial conditions.

scholarly journals Spatio-temporal development of large scale auroral electrojet currents relative to substorm onsets

2021 ◽  
Author(s):  
Sebastian Käki ◽  
Ari Viljanen ◽  
Liisa Juusola ◽  
Kirsti Kauristie
Keyword(s):  
Large Scale ◽  
Current System ◽  
Field Measurements ◽  
Low Earth Orbit ◽  
Satellite Mission ◽  
Low Earth Orbit Satellites ◽  
Spatio Temporal ◽  
Substorm Onsets ◽  
Auroral Current ◽  
Swarm Satellite

Abstract. During auroral substorms the electric currents flowing in the ionosphere change rapidly and a large amount of energy is dissipated in the auroral ionosphere. An important part of the auroral current system are the auroral electrojets whose profiles can be estimated from magnetic field measurements from Low Earth Orbit satellites. In this paper we combine electrojet data derived from the Swarm satellite mission of ESA with the substorm database derived from the SuperMAG ground magnetometer network data. We organize the electrojet data in relation to the location and time of the onset and obtain statistics for the development of the integrated current and latitudinal location for the auroral electrojets relative to the onset. The major features of the behaviour of the westward electrojet are found to be in accordance with earlier studies of field aligned currents and ground magnetometer observations of substorm time statistics. In addition we show that after the onset the latitudinal location of the maximum of the westward electrojet determined from Swarm satellite data is mostly located close to the SuperMAG onset latitude in the local time sector of the onset regardless of where the onset happens. We also show that the SuperMAG onset corresponds to a strengthening of the order of 100 kA in the amplitude of the median of the westward integrated current in the Swarm data from 15 minutes before to 15 minutes after the onset.

scholarly journals Geomagnetic Virtual Observatories: Global monitoring of geomagnetic secular variation with Swarm data

2020 ◽  
Author(s):  
Magnus Hammer ◽  
Christopher Finlay ◽  
Ciaran Beggan ◽  
William Brown ◽  
Grace Cox
Keyword(s):  
Magnetic Field ◽  
Time Series ◽  
Local Time ◽  
Secular Variation ◽  
Field Measurements ◽  
Magnetic Data ◽  
Related Phenomenon ◽  
Virtual Observatory ◽  
Data Products ◽  
Virtual Observatories

<p>The ESA Swarm DISC Geomagnetic Virtual Observatories (GVO) project aims to apply the virtual observatory concept to Swarm magnetic field measurements. The Virtual Observatory concept is a data processing method which mimics the behavior of magnetic monthly-mean time-series measured at ground observatories but at fixed locations on a uniform global grid at satellite altitude instead. Here we present several new GVO data products consisting of the average time-series of vector magnetic field values, regularly distributed in space and time which are suitable for monitoring the geomagnetic field. The GVO products consist of an equal-area grid with separation spacing of 300 km and cadence of either 1 month or 4 months. Various levels of processing are applied to remove the effects of altitude change and satellite local-time differences to produce a consistent time series. It is known that monthly time-series can have strong local-time artifacts which are removed with four-monthly averages, though with a loss of temporal resolution. The GVO products are designed to make Swarm magnetic data more accessible to researchers studying the physics of the core dynamo process, and related phenomenon such are secular variation, geomagnetic jerks and rapid core dynamics. In addition, the GVO data products also provide valuable information for investigating magnetospheric and ionospheric magnetic signals on timescales of months and longer.</p>

Spatio-temporal development of large scale auroral electrojet currents relative to substorm onsets

2021 ◽  
Author(s):  
Sebastian Käki ◽  
Ari Viljanen ◽  
Liisa Juusola ◽  
Kirsti Kauristie
Keyword(s):  
Large Scale ◽  
Current System ◽  
Field Measurements ◽  
Low Earth Orbit ◽  
Satellite Mission ◽  
Low Earth Orbit Satellites ◽  
Spatio Temporal ◽  
Substorm Onsets ◽  
Auroral Current ◽  
Swarm Satellite

<p>The electric currents flowing in the ionosphere change rapidly and a large amount of energy is dissipated in the auroral ionosphere during auroral substorms. An important part of the auroral current system are the auroral electrojets whose profiles can be estimated from magnetic field measurements from low Earth orbit satellites. We have combined electrojet data derived from the Swarm satellite mission of ESA with the substorm database derived from the SuperMAG ground network data. We organize the electrojet data in relation to the location of the onset and obtain statistics for the development of the integrated current and latitudinal location for the auroral electrojets relative to the onset. Especially we show that just after the onset the latitudinal location of the maximum of the westward electrojet determined from Swarm satellite data is mostly located close to the onset latitude in the local time sector of the onset regardless of where the onset happens.</p>

scholarly journals A machine learning approach for automated ULF wave recognition

2019 ◽  
Vol 9 ◽  
pp. A13 ◽  
Author(s):  
Georgios Balasis ◽  
Sigiava Aminalragia-Giamini ◽  
Constantinos Papadimitriou ◽  
Ioannis A. Daglis ◽  
Anastasios Anastasiadis ◽  
...  
Keyword(s):  
Machine Learning ◽  
Low Frequency ◽  
Field Measurements ◽  
Low Earth Orbit ◽  
Space Physics ◽  
Machine Learning Techniques ◽  
Ulf Waves ◽  
Strong Impact ◽  
Analysis Tool ◽  
Champ Satellite

Machine learning techniques have been successfully introduced in the fields of Space Physics and Space Weather, yielding highly promising results in modeling and predicting many disparate aspects of the geospace environment. Magnetospheric ultra-low frequency (ULF) waves can have a strong impact on the dynamics of charged particles in the radiation belts, which can affect satellite operation. Here, we employ a method based on Fuzzy Artificial Neural Networks in order to detect ULF waves in the time series of the magnetic field measurements on board the low-Earth orbit CHAMP satellite. The outputs of the method are validated against a previously established, wavelet-based, spectral analysis tool, that was designed to perform the same task, and show encouragingly high scores in the detection and correct classification of these signals.

scholarly journals Geomagnetic Virtual Observatories: monitoring geomagnetic secular variation with the Swarm satellites

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Magnus D. Hammer ◽  
Grace A. Cox ◽  
William J. Brown ◽  
Ciarán D. Beggan ◽  
Christopher C. Finlay
Keyword(s):  
Time Series ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Time Windows ◽  
Low Earth Orbit ◽  
Data Selection ◽  
Spherical Harmonic Analysis ◽  
Core Field ◽  
The Core ◽  
Swarm Satellites

AbstractWe present geomagnetic main field and secular variation time series, at 300 equal-area distributed locations and at 490 km altitude, derived from magnetic field measurements collected by the three Swarm satellites. These Geomagnetic Virtual Observatory (GVO) series provide a convenient means to globally monitor and analyze long-term variations of the geomagnetic field from low-Earth orbit. The series are obtained by robust fits of local Cartesian potential field models to along-track and East–West sums and differences of Swarm satellite data collected within a radius of 700 km of the GVO locations during either 1-monthly or 4-monthly time windows. We describe two GVO data products: (1) ‘Observed Field’ GVO time series, where all observed sources contribute to the estimated values, without any data selection or correction, and (2) ‘Core Field’ GVO time series, where additional data selection is carried out, then de-noising schemes and epoch-by-epoch spherical harmonic analysis are applied to reduce contamination by magnetospheric and ionospheric signals. Secular variation series are provided as annual differences of the Core Field GVOs. We present examples of the resulting Swarm GVO series, assessing their quality through comparisons with ground observatories and geomagnetic field models. In benchmark comparisons with six high-quality mid-to-low latitude ground observatories we find the secular variation of the Core Field GVO field intensities, calculated using annual differences, agrees to an rms of 1.8 nT/yr and 1.2 nT/yr for the 1-monthly and 4-monthly versions, respectively. Regular sampling in space and time, and the availability of data error estimates, makes the GVO series well suited for users wishing to perform data assimilation studies of core dynamics, or to study long-period magnetospheric and ionospheric signals and their induced counterparts. The Swarm GVO time series will be regularly updated, approximately every four months, allowing ready access to the latest secular variation data from the Swarm satellites.

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