Investigating the auroral electrojets with low altitude polar orbiting satellites

Moretto, T.; Olsen, Nils; Ritter, Patricia; Lu, G.

doi:10.5194/angeo-20-1049-2002

Cited by 18 publications

(21 citation statements)

References 34 publications

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“…We assume that in the polar regions the Hall currents can be approximated by a series of infinite line currents. This method has been developed and tested with Magsat and Ørsted data (Olsen, 1996;Moretto et al, 2002). For our computations the line currents are placed at a height of 110 km and they are separated by 1 • in latitude over an interval of ±80 • , centered at the closest approach of the satellite track to the geographic pole.…”

Section: Ionospheric Hall Current Determined From Champ Datamentioning

confidence: 99%

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Ionospheric currents estimated simultaneously from CHAMP satelliteand IMAGE ground-based magnetic field measurements: a statisticalstudy at auroral latitudes

et al. 2004

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Abstract.One important contribution to the magnetic field measured at satellite altitude and at ground level comes from the external currents. We used the total field data sampled by the Overhauser Magnetometer on CHAMP and the horizontal magnetic field measurements of the IMAGE groundbased magnetometer network to study the ionospheric Hall current system in the auroral regions. For the CHAMP data a current model consisting of a series of lines and placed at a height of 110 km is fitted to the magnetic field signature sampled on the passage across the polar region. The derived current distributions depend, among others, on season and on the local time of the satellite track. At dawn/dusk the auroral electrojets can be detected most clearly in the auroral regions. Their intensity and location are evidently correlated with the AE activity index. For a period of almost two years the results obtained from space and the currents determined from ground-based observations are studied. For the full IMAGE station array a newly-developed method of spherical elementary current systems (SECS) is employed to compute the 2-D equivalent current distribution, which gives a detailed picture of an area covering latitudes 60 • − 80 • N and 10 • − 30 • E in the auroral region. Generally, the current estimates from satellite and ground are in good agreement. The results of this survey clearly show the average dependence of the auroral electrojet on season and local time. This is particularly true during periods of increased auroral activity. The correlation coefficient of the results is close to one in the region of sizeable ionospheric current densities. Also the ratio of the current densities, as determined from above and below the ionosphere, is close to unity. It is the first time that the method of Hall current estimate from a satellite has been validated quantitatively by ground-based observations. Among others, this result is of interest for magnetic main field modelling, since it demonstrates that ground-based observations can be used to predict electrojet signatures in satellite magnetic field scalar data.

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Section: Ionospheric Hall Current Determined From Champ Datamentioning

confidence: 99%

“…The possibility of deriving horizontal ionospheric current estimates from the magnetic field scalar data was first demonstrated by Olsen (1996), who also employed Magsat data. In a later study, Moretto et al (2002) applied this technique to data from other satellites.…”

Section: Introductionmentioning

confidence: 99%

Ionospheric currents estimated simultaneously from CHAMP satelliteand IMAGE ground-based magnetic field measurements: a statisticalstudy at auroral latitudes

et al. 2004

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“…The technique of determining the current strength of each line by inverting the variations in the total magnetic field has been developed by Olsen (1996). Moretto et al (2002) has applied this method later to Ørsted data. The reliability of this approach has been demonstrated in a statistical study where current density estimates from CHAMP were directly compared with independent determinations from ground (Ritter et al, 2004).…”

Section: Instrumentation and Data Processingmentioning

confidence: 99%

Storm time dynamics of auroral electrojets: CHAMP observation and the Space Weather Modeling Framework comparison

et al. 2008

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Abstract. We investigate variations of the location and intensity of auroral currents during two magnetic storm periods based on magnetic field measurements from CHAMP separately for both hemispheres, as well as for the dayside and nightside. The corresponding auroral electrojet current densities are on average enhanced by about a factor of 7 compared to the quiet time current strengths. The nightside westward current densities are on average 1.8 (2.2) times larger than the dayside eastward current densities in the Northern (Southern) Hemisphere. Both eastward and westward currents are present during the storm periods with the most intense electrojets appearing during the main phase of the storm, before the ring current maximizes in strength. The eastward and westward electrojet centers can expand to 55 • MLat during intense storms, as is observed on 31 March 2001 with D st =−387 nT. The equatorward shift of auroral currents on the dayside is closely controlled by the southward IMF, while the latitudinal variations on the nightside are better described by the variations of the D st index. However, the equatorward and poleward motion of the nightside auroral currents occur earlier than the D st variations. The Space Weather Modeling Framework (SWMF) can capture the general dynamics of the storm time current variations. Both the model and the actual data show that the currents tend to saturate when the merging electric field is larger than 10 mV/m. However, the exact prediction of the temporal development of the currents is still not satisfactory.

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“…The use of scalar magnetic satellite data is a simplification compared to using the full vector data, resulting in similar results to a ground magnetic chain. The line current method has been applied to multi-satellite data by Olsen et al (2002) and Moretto et al (2002). Juusola et al (2006) proposed an alternative approach for monitoring the auroral activity from magnetic satellite data.…”

Section: Introductionmentioning

confidence: 99%

Determining polar ionospheric electrojet currents from Swarm satellite constellation magnetic data

2016

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We determine the strength and location of the ionospheric currents responsible for the polar electrojets from magnetic data collected by the Swarm satellite constellation on an orbit-by-orbit basis. The ionospheric currents are modelled using a simple, yet robust, method by a series of line currents at 110 km altitude (corresponding to the ionospheric E-layer) perpendicular to the satellite orbit, separated by 1 • (about 113 km). We assess the reliability of our method, with the aim of a possible near-real-time application. A study of the effect of different regularization methods is therefore carried out. An L 1 model regularization of the second-order spatial differences, and robust treatment of the data (to account for non-Gaussian error distributions), yields the most encouraging results. We apply our approach to two three-weekly data periods in March 2014 (geomagnetic quiet conditions) and March 2015 (more disturbed conditions), respectively. Our orbit-by-orbit approach also allows the temporal evolution of the polar electrojets to be investigated. We find remarkable agreement of the ionospheric activity in Northern and Southern polar regions, with correlation exceeding 0.9 for periods longer than two days. Reliability of the approach is shown by three key results: (1) a common regularization parameter for all orbits with enough data coverage, (2) 0.95 squared coherence with the Auroral Electrojet index, and (3) 0.97 squared coherence is found between the side-by-side flying satellites, Alpha and Charlie, indicating a method invariant to small changes in data input. All these results indicate a possible automated near-real-time application.

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Investigating the auroral electrojets with low altitude polar orbiting satellites

Cited by 18 publications

References 34 publications

Ionospheric currents estimated simultaneously from CHAMP satelliteand IMAGE ground-based magnetic field measurements: a statisticalstudy at auroral latitudes

Ionospheric currents estimated simultaneously from CHAMP satelliteand IMAGE ground-based magnetic field measurements: a statisticalstudy at auroral latitudes

Storm time dynamics of auroral electrojets: CHAMP observation and the Space Weather Modeling Framework comparison

Determining polar ionospheric electrojet currents from Swarm satellite constellation magnetic data

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