Examining the Magnetic Signal Due To Gravity and Plasma Pressure Gradient Current With the TIE‐GCM

• Published in: Journal of geophysical research. Space physics 2017-12, Vol.122 (12), p.12,486-12,504
• Main Authors: Maute, A., Richmond, A. D.
• Format: Article
• Language: English
• Subjects: Approximation; Computer simulation; Diamagnetism; Earth orbits; Electric fields; F region; Geomagnetic field; Gravity currents; gravity‐driven current; ionospheric current; Ionospheric currents; Low earth orbits; Magnetic fields; magnetic perturbation; Mathematical analysis; Mathematical models; Plasma; Plasma pressure; plasma pressure gradient current; Pressure effects; Signal strength; Solar cycle; Solar magnetic field; Solar maximum; Solar minimum
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2017JA024841

Accurate magnetic field measurements at ground and low‐Earth orbit (LEO) are crucial to describe Earth's magnetic field. One of the challenges with processing LEO magnetic field measurements to study Earth's magnetic field is that the satellite flies in regions of highly varying ionospheric currents, which needs to be characterized accurately. The present study focuses on ionospheric current systems due to gravity and plasma pressure gradient forcing and aims to provide guidance on the estimation of their magnetic effect at LEO altitudes with the help of numerical modeling. We assess the diamagnetic approximation that estimates the magnetic signal of the plasma pressure gradient current. The simulations indicate that the diamagnetic effect should not be removed from LEO magnetic observations without considering the gravity current effect, as this will lead to an error larger than the magnetic signal of these currents. We introduce and evaluate a method to capture the magnetic effect of the gravity‐driven current. The diamagnetic and gravity current approximations ignore the magnetic effect from currents set up by the induced electric field. The combined gravity and plasma pressure gradient magnetic effect tends to cancel above the F region peak; however, between approximately 300 km and the peak it exhibits a significant height and latitudinal variation with magnitudes up to 8 nT. During solar minimum the combined magnetic signal is less than 1 nT above 300 km. In addition to the solar cycle dependence, the magnetic signal strength varies with longitude (approximately by 50%) and season (up to 80%) at solar maximum. Plain Language Summary Accurate magnetic field measurements at ground and low‐Earth orbit (LEO) are crucial to describe Earth's magnetic field. One of the challenges with processing LEO magnetic field measurements to study Earth's magnetic field is that the satellite flies in regions of highly varying ionospheric currents. The ionospheric signals need to be removed from the measurements to isolate the signal from the Earth's magnetic field. Therefore, it is crucial to describe the ionospheric current accurately. The present study focuses on the ionospheric current systems due to gravity and plasma pressure gradient forcing and aims to provide guidance on the estimation of their magnetic effect at LEO altitudes. We assess the diamagnetic approximation which estimates the magnetic signal of the plasma pressure gradient current. And we introduce a