11:00 〜 13:00
[PEM10-P17] Comparison of Magnetic Variations Associated with the IHFAC Observed on the Ground and in the LEO
キーワード：IHFAC、地球低軌道、地磁気観測
A global distribution of the ionospheric current has been studied by many investigators to understand the potential balance which is subsequentially produced by the tidal variations in the neutral atmosphere and imposed electric field from the magnetospheric disturbances. A primary vortex pattern of the current system is known as Sq current system which has potential peak near 20-30 deg in geomagnetic latitude at near noon sector. However, the potential pattern shows the north/south asymmetry depending on the season, that is, the intensity of the potential is stronger (weaker) in summer (winter) hemisphere. Regarding to such potential pattern, Fukushima (1979, 1991) theoretically predicted an existence of Inter-Hemispheric Field Aligned Currents (IHFAC) connecting between the potential peaks in both northern and southern hemispheres. However, the detailed morphology and physical process of the IHFAC have not been fully understand, though there were several ground and satellites observations (e.g. Yamashita and Iyemori, 2002, and Park et al., 2002).
Recently Ranasinghe et al.(2021) analyze a long term variation of the D-component magnetic variation at Davao (Geographical latitude 7 deg., Geographical longitude 124.5, Geomagnetic latitude -2.22 deg, Geomagnetic longitude 197.9 deg, Dip latitude -0.24 deg), and indicates that the direction of the IHFAC in the different local time shows the obvious seasonal variations. In particular, the obtained directions of IHFAC at the evening sector during September – November shows southward, which is inconsistent with the IHFAC model proposed by Fukushima (1979, 1991).
In this study, we analyze the data of Vector Field Magnetometer (VFM) onboard the Swam satellites to compare the characteristics of the IHFAC obtained from ground magnetometer data. The E-component (eastward) magnetic field variations in the NEC coordinate system from 2014 to 2021 is used in this study. We calculate the magnetic data obtained at a confined region of -5 < Lat < 5 (degree), and 115 < Long < 135 (degree) where Davao station is mostly centered.
As a result, the E-component magnetic field shows positive deviations in the dusk sectors from September to December, whereas it shows negative deviations from May to July. This signature is basically consistent with the observation on the ground by Ranasinghe et al. The result suggests the altitude of the IHFAC at equatorial region is higher than 510km of the altitude of Swam orbit. Moreover, this study implies the possibility to the more affordable observation in LEO by nano-satellites.
Recently Ranasinghe et al.(2021) analyze a long term variation of the D-component magnetic variation at Davao (Geographical latitude 7 deg., Geographical longitude 124.5, Geomagnetic latitude -2.22 deg, Geomagnetic longitude 197.9 deg, Dip latitude -0.24 deg), and indicates that the direction of the IHFAC in the different local time shows the obvious seasonal variations. In particular, the obtained directions of IHFAC at the evening sector during September – November shows southward, which is inconsistent with the IHFAC model proposed by Fukushima (1979, 1991).
In this study, we analyze the data of Vector Field Magnetometer (VFM) onboard the Swam satellites to compare the characteristics of the IHFAC obtained from ground magnetometer data. The E-component (eastward) magnetic field variations in the NEC coordinate system from 2014 to 2021 is used in this study. We calculate the magnetic data obtained at a confined region of -5 < Lat < 5 (degree), and 115 < Long < 135 (degree) where Davao station is mostly centered.
As a result, the E-component magnetic field shows positive deviations in the dusk sectors from September to December, whereas it shows negative deviations from May to July. This signature is basically consistent with the observation on the ground by Ranasinghe et al. The result suggests the altitude of the IHFAC at equatorial region is higher than 510km of the altitude of Swam orbit. Moreover, this study implies the possibility to the more affordable observation in LEO by nano-satellites.