The role of high-resolution geomagnetic field models for investigating ionospheric currents at low Earth orbit satellites

Abstract

Low Earth orbiting geomagnetic satellite missions, such as the Swarm satellite mission, are the only means to monitor and investigate ionospheric currents on a global scale and to make in situ measurements of F region currents. High-precision geomagnetic satellite missions are also able to detect ionospheric currents during quiet-time geomagnetic conditions that only have few nanotesla amplitudes in the magnetic field. An efficient method to isolate the ionospheric signals from satellite magnetic field measurements has been the use of residuals between the observations and predictions from empirical geomagnetic models for other geomagnetic sources, such as the core and lithospheric field or signals from the quiet-time magnetospheric currents. This study aims at highlighting the importance of high-resolution magnetic field models that are able to predict the lithospheric field and that consider the quiet-time magnetosphere for reliably isolating signatures from ionospheric currents during geomagnetically quiet times. The effects on the detection of ionospheric currents arising from neglecting the lithospheric and magnetospheric sources are discussed on the example of four Swarm orbits during very quiet times. The respective orbits show a broad range of typical scenarios, such as strong and weak ionospheric signal (during day-and nighttime, respectively) superimposed over strong and weak lithospheric signals. If predictions from the lithosphere or magnetosphere are not properly considered, the amplitude of the ionospheric currents, such as the midlatitude Sq currents or the equatorial electrojet (EEJ), is modulated by 10-15 % in the examples shown. An analysis from several orbits above the African sector, where the lithospheric field is significant, showed that the peak value of the signatures of the EEJ is in error by 5 % in average when lithospheric contributions are not considered, which is in the range of uncertainties of present empirical models of the EEJ.

A brief review of equatorial ionization anomaly and ionospheric irregularities

“…Numerous papers on different aspects of spread-F, plasma bubbles and scintillations under magnetically quiet and active conditions have been reported using ionosondes, radars, optical imagers, rockets and satellites (e.g., Farley et al, 1970;Rastogi et al, 1981;Abdu et al, 1983;Tulasi Ram et al, 2008). Satellite observations, especially, have provided a clear picture of the climatology of the irregularities (e.g., Burke et al, 2004;Stolle et al, 2016;Su et al, 2006).…”

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…So far there is no review on the satellite observations of the global Sq field. Thus, interested readers are referred to recent articles by Stolle et al (2016) and Chulliat et al (2016). Finally, the scope of this review is not limited to geomagnetically quiet periods.…”

Analysis of the Impact of Long‐Term Changes in the Geomagnetic Field on the Spatial Pattern of the Weddell Sea Anomaly

“…One can notice that the TIEGCM‐derived index has smaller amplitudes when compared with Swarm and CHAMP. As shown by Stolle et al (2016), the IGRF model that is implemented in TIEGCM provides only representation of the main magnetic field (spherical harmonics up to degree 13) and does not contain contribution from external sources, lithospheric field, and the quiet‐time magnetospheric field. In consequence, model‐derived index will not be able to fully reproduce such plasma density structures that can be associated with ionospheric currents occurring at low‐latitude and midlatitude of the F‐region.…”