Electrojet Estimates From Mesospheric Magnetic Field Measurements

Abstract

The first attempts to relate ground magnetic disturbances to electric currents in space were carried out more than a century ago. Birkeland (1908) presented a horizontal two-cell equivalent current system which is reminiscent of maps derived from modern magnetometer networks (Waters et al., 2015). Birkeland further proposed a three-dimensional (3D) structure of the space currents that involved magnetic field-aligned currents. This idea remained controversial until it was confirmed by early magnetometer measurements in space (Zmuda et al., 1966). We now view the 3D ionospheric current system as composed of Birkeland currents, that flow along magnetic field lines, and a horizontal current that is confined to a thin conducting layer of the ionosphere, mainly around 100-120 km altitude. The relationship between ground magnetic field observations and this 3D current system is ambiguous, and we therefore often interpret ground magnetic field observations in terms of an equivalent 2D current system. At high latitudes, the equivalent current is nearly identical with the divergence-free part of the horizontal current (e.g., Fukushima, 1976;Untiedt & Baumjohann, 1993). In this study, we use the term electrojet as synonymous with the equivalent current, although it is sometimes used to refer to specific parts of it.

Transient high latitude geomagnetic response to rapid increases in solar wind dynamic pressure

“…This method is implemented by Laundal et al (2022); they combine magnetic perturbation and convection measurements from space and ground with conductance measurements via ionospheric Ohm's law to significantly improve data coverage and information retrieved. This will be a very useful tool when the EZIE satellite mission (Laundal et al, 2021) launches in the near future providing measurements of the magnetic field in the mesosphere. In the future we intend to carry out a regional analysis of events to study their variation in more detail.…”

Local Mapping of Polar Ionospheric Electrodynamics

“…Another example is the upcoming EZIE satellites, which will scan the magnetic field disturbances in the mesosphere as the satellites move. EZIE alone gives the equivalent divergence‐free current (Laundal et al., 2021 ), and the Lompe technique can be used to combine EZIE data with other data sources to find the convection and FACs. Yet another use case could be for theoretical analyses and interpretations.…”

“…This regularization technique was also used in the Observing System Simulation Experiment carried out for the EZIE (Laundal et al., 2021 ), an NASA mission planned for launch in 2024. We plan to explore alternative methods in future applications of the Lompe technique.…”

“…In addition to the nonuniform data distribution on a global scale, there are certain measurements that can resolve very small‐scale structures, which would also benefit from analysis techniques with high spatial resolution. Examples include convection and conductivity measurements in the field of view of phased array incoherent scatter radars, conductance distributions based on optical measurements from GBOs (Clayton et al., 2019 ; Grubbs et al., 2018 ), and high‐resolution scans of the mesospheric magnetic field along the track of the upcoming Electrojet Zeeman Imaging Explorer (EZIE) satellites (Laundal et al., 2021 ; Yee et al., 2017 ).…”

“…Historically SECS analysis has been used mostly for regional studies of equivalent currents (e.g., Amm, 1997 ; Amm & Viljanen, 1999 ; Amm et al., 2002 ; Laundal et al., 2021 ; Weygand et al., 2011 ). However, global studies are also possible (Juusola et al., 2014 ).…”