Modeling the Climatology of Low‐ and Mid‐Latitude F‐Region Ionospheric Currents Using the Swarm Constellation

Abstract

The Earth's magnetic field is the sum of magnetic fields produced by many different sources. It can be measured at the Earth's surface, in the geomagnetic observatories, or on board of satellites (Hulot et al., 2015). Such data are used to build models of the Earth's magnetic field and to study their sources. One main challenge, however, is to single out the signal from each source. This is particularly true for the ionospheric field produced by the electric currents that flow in the ionosphere-the ionized layer of the atmosphere, from 80 to 1,000 km. Because of its high variability in space and time, and of an incomplete space-time data coverage, this field and associated electric currents are still only partially understood (Finlay et al., 2017).One of the dominant ionospheric currents at mid and low latitudes are called Solar quiet (Sq) currents (Matsushita, 1968;Yamazaki & Maute, 2017). They flow in the ionospheric E region-between 90 and 150 kmand mainly consist of two vortices, each flowing in one hemisphere and in opposite directions. They are generated by a physical mechanism called the ionospheric wind dynamo (Richmond, 1979) and are therefore referred to as dynamo currents. This system is reinforced at the magnetic equator where the equatorial electrojet flows (Lühr et al., 2021). Several approaches have been proposed to build data-based models of the mid-and low-latitude E-region ionospheric field. The Comprehensive Model series (Sabaka et al., 2002(Sabaka et al., , 2020 and the DIFI model (Chulliat et al., 2013(Chulliat et al., , 2016 use spherical harmonics and Fourier series to represent the global climatological variations of the low and mid latitude E-region ionospheric field. More recently, some alternative approaches were developed. They rely on a priori information allowing for a better characterization of individual Earth's magnetic field component. Among these, one can mention correlation-based modeling techniques (Baerenzung et al., 2020;Holschneider et al., 2016) and techniques that rely on physics-based models (Alken et al., 2017;Egbert et al., 2021).Other important ionospheric currents flow in the F region, between 150 and 1,000 km. These currents are of particular interest to this study. The dominant currents in the F region are the field-aligned currents that flow along the highly conductive field lines of the Earth's main magnetic field. They exist both at high latitudes

Quasi 16‐Day Wave Signatures in the Interhemispheric Field Aligned Currents: A New Perspective Toward Atmosphere‐Ionosphere Coupling

“…IHFACs are predominantly confined to the dayside and are strongest at low latitudes (below ± 35°magnetic latitudes). Their intensity and direction (northward or southward) are dependent on latitude, longitude, local time, and season (Fillion et al, 2023;Park et al, 2011Park et al, , 2020Wang et al, 2023). Model studies carried out by Fukushima (1979) suggested that the most intense IHFACs are located around the Sq focus in two hemispheres, flowing from the summer to the winter hemisphere during noon hours.…”

A Model of Hourly Variations of the Near‐Earth Magnetic Field Generated in the Inner Magnetosphere and Its Induced Counterpart

“…For example, due to the overlap of its spatial scales with those of the core field on the night side of the Earth, accurately removing the magnetospheric field is an essential step in building modern core field models used to constrain physical processes in the Earth's core and the geodynamo (Finlay et al, 2017). Magnetospheric field models are also used in ionospheric magnetic field and electrodynamics studies (Fillion et al, 2023;Stolle et al, 2016). Additionally, in a certain frequency range, the near-Earth magnetospheric field is one of the main sources for the electromagnetic induction studies of the Earth's interior (A.…”