Spherical Cap Harmonic Analysis Techniques for Mapping High-Latitude Ionospheric Plasma Flow—Application to the Swarm Satellite Mission

Fiori, R. A. D.

doi:10.1007/978-3-030-26732-2_9

“…Since the electrojets typically follow lines of constant magnetic latitude, they have relatively simple spatial flow patterns, and line current models are particularly suitable for their study. For current systems which have more spatial complexity, such as Sq, pressure-gradient currents, interhemispheric field-aligned currents (IHFAC), and high-latitude field-aligned currents (FAC), it is necessary to utilize other methods to determine equivalent current flow, such as spectral methods (Fiori and Boteler 2018) or spherical elementary current systems (SECS) (Vanhamäki et al 2018). This chapter will follow the work of Alken et al (2013aAlken et al ( , 2014 in order to define line currents which follow lines of constant quasi-dipole (QD) latitude in the equatorial region to estimate realistic EEJ equivalent current flow.…”

Section: Introductionmentioning

confidence: 99%

Estimating Currents and Electric Fields at Low Latitudes from Satellite Magnetic Measurements

Alken

¹

2019

Ionospheric Multi-Spacecraft Analysis Tools

View full text Add to dashboard Cite

Low-latitude ionospheric electric currents produce prominent signatures in the magnetic field measurements made by low Earth-orbiting satellites. Analyzing these magnetic signatures not only provides insight into the currents themselves, but also many other important and interesting phenomena in the low-latitude ionosphere and thermosphere. The low-latitude currents are modulated by thermospheric winds, so attaining a global knowledge of the spatial structure of the currents can give insight into the neutral tidal harmonics present at ionospheric altitudes. Furthermore, the equatorial electrojet (EEJ) current is driven by an equatorial electric field which in turn is generated by a dynamo process. This electric field is additionally responsible for the vertical plasma fountain and equatorial ionization anomaly at low-latitudes. Magnetic measurements of the EEJ, therefore, allows the study of low-latitude plasma motion in the E and F regions of the ionosphere. This chapter will present techniques developed for processing magnetic measurements of the EEJ to extract information about the low-latitude currents and their driving electric fields. This chapter will present a line current approach to recover the EEJ current strengths, with an emphasis on cleaning the satellite data and minimizing magnetic fields from other internal and external sources. The electric fields will be determined using a combination of physical modeling and fitting the EEJ current strengths from the satellite measurements.

show abstract

“…In SCHA modelling, the spherical cap corresponds to an area defined around a selected point by a predetermined angle 0 subtended at the centre of the Earth. The spherical cap half-angle size has to be large enough because some errors will arise when attempting to map wavelengths that are larger than the spherical cap (Fiori, 2020). The area modelled in this thesis is the Indonesian region with a spherical cap half-angle 30°, and the coordinate of the spherical cap pole is at 122°E and 3°S.…”

Section: List Of Figuresmentioning

confidence: 99%

“…The spatial truncation index ( ) and order ( ) in SCHA describe the sectioning over the spherical cap. This division defines the resolution of the features that can be mapped using SCHA (Fiori, 2020).…”

Section: Spherical Cap Harmonic Analysis (Scha)mentioning

confidence: 99%

“…A conical section with a radius constructs the spherical cap from a sphere and in consideration of the outer slab of the section which extends from the radius a to b as has been described by Fiori (2020) and can be seen in Figure 7. Consider an arbitrary point P in the geographic coordinate system which has coordinate ( , ) and the spherical cap pole with coordinate ( , ).…”

Section: Coordinate Rotationmentioning

confidence: 99%

“…Spherical cap structure, fromFiori (2020). The domain of study is bounded by the terrestrial surface and the upper surface with spherical cap half-angle 0 .From the spherical cap coordinate system, the transformed longitude and colatitude for any data site can be found by considering a triangle on the Earth's surface with the centre of the spherical cap, the North geographic pole, and the data points as shown inFigure 8.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Investigation of Regional Geomagnetic Field Modelling in Indonesia

Setiawan¹

0

View full text Add to dashboard Cite

<p>This thesis deals with the application of the Spherical Cap Harmonic Analysis (SCHA) modelling technique to obtain geomagnetic field models for Indonesia, which have better resolution and accuracy than the International Geomagnetic Reference Field (IGRF). B-splines basis function and autoregressive forecasting are applied to improve estimates of secular variation and its forecast over the Indonesian region. The modelling technique is applied to geomagnetic observation data compiled from 68 geomagnetic repeat stations in Indonesia covering the period 1985 - 2015 from BMKG (Badan Meteorologi Klimatologi dan Geofisika / Agency for Meteorology, Climatology, and Geophysics) Indonesia, definitive data from five BMKG geomagnetic observatories and 13 INTERMAGNET (The International Real-Time Magnetic Observatory Network) observatories. Synthetic cartesian X, Y, and Z components at sea level at 17 fixed locations, calculated from IGRF-13, are also used. The area covered by the models in this thesis is the Indonesian region with a spherical cap half-angle of 30° and with the coordinate of the spherical cap pole at 122°E and 3°S. From statistical analysis and comparison with the IGRF, the SCHA model with index k = 7 is considered as the best SCHA model, both in resolution and accuracy. Compared with the root mean square deviation (RMSD) of the IGRF model, the RMSD of the SCHA model with index k = 7 is lower by 28 nT, 11 nT, and 34 nT for X, Y, and Z components, respectively. A model from interpolation of the SCHA with index k = 7 using the B-splines basis function for the year 1985.5 – 2015.5 shows that the SCHA model gives better results than the IGRF. The forecasting calculation for the year 2015.5 – 2020.5 suggests that the autoregressive order 3 of the SCHA with index k = 7 gives better results than the forecasting of the IGRF model, especially in the X, Z, and F components. However, in the Y component, the IGRF is still better than the SCHA model. The RMSD of the forecasted SCHA model is 154.92 nT, 200.87 nT, 104.39 nT, and 135.81 nT for X, Y, Z, and F components, respectively, while the RMSD of the IGRF model is 172.62 nT, 95.52 nT, 117.55 nT, and 162.38 nT for X, Y, Z, and F components. Thus, the forecasted SCHA model is suitable for data reduction of geomagnetic surveys in the Indonesian region but not preferable for navigation.</p>

show abstract

Investigation of Regional Geomagnetic Field Modelling in Indonesia

Setiawan¹

0

View full text Add to dashboard Cite

<p>This thesis deals with the application of the Spherical Cap Harmonic Analysis (SCHA) modelling technique to obtain geomagnetic field models for Indonesia, which have better resolution and accuracy than the International Geomagnetic Reference Field (IGRF). B-splines basis function and autoregressive forecasting are applied to improve estimates of secular variation and its forecast over the Indonesian region. The modelling technique is applied to geomagnetic observation data compiled from 68 geomagnetic repeat stations in Indonesia covering the period 1985 - 2015 from BMKG (Badan Meteorologi Klimatologi dan Geofisika / Agency for Meteorology, Climatology, and Geophysics) Indonesia, definitive data from five BMKG geomagnetic observatories and 13 INTERMAGNET (The International Real-Time Magnetic Observatory Network) observatories. Synthetic cartesian X, Y, and Z components at sea level at 17 fixed locations, calculated from IGRF-13, are also used. The area covered by the models in this thesis is the Indonesian region with a spherical cap half-angle of 30° and with the coordinate of the spherical cap pole at 122°E and 3°S. From statistical analysis and comparison with the IGRF, the SCHA model with index k = 7 is considered as the best SCHA model, both in resolution and accuracy. Compared with the root mean square deviation (RMSD) of the IGRF model, the RMSD of the SCHA model with index k = 7 is lower by 28 nT, 11 nT, and 34 nT for X, Y, and Z components, respectively. A model from interpolation of the SCHA with index k = 7 using the B-splines basis function for the year 1985.5 – 2015.5 shows that the SCHA model gives better results than the IGRF. The forecasting calculation for the year 2015.5 – 2020.5 suggests that the autoregressive order 3 of the SCHA with index k = 7 gives better results than the forecasting of the IGRF model, especially in the X, Z, and F components. However, in the Y component, the IGRF is still better than the SCHA model. The RMSD of the forecasted SCHA model is 154.92 nT, 200.87 nT, 104.39 nT, and 135.81 nT for X, Y, Z, and F components, respectively, while the RMSD of the IGRF model is 172.62 nT, 95.52 nT, 117.55 nT, and 162.38 nT for X, Y, Z, and F components. Thus, the forecasted SCHA model is suitable for data reduction of geomagnetic surveys in the Indonesian region but not preferable for navigation.</p>

show abstract

Spherical Cap Harmonic Analysis Techniques for Mapping High-Latitude Ionospheric Plasma Flow—Application to the Swarm Satellite Mission

Cited by 6 publications

References 75 publications

Estimating Currents and Electric Fields at Low Latitudes from Satellite Magnetic Measurements

Estimating Currents and Electric Fields at Low Latitudes from Satellite Magnetic Measurements

Investigation of Regional Geomagnetic Field Modelling in Indonesia

Investigation of Regional Geomagnetic Field Modelling in Indonesia

Contact Info

Product

Resources

About