Examining the magnetic signal due to gravity and plasma pressure gradient current with the TIE-GCM

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Thursday, December 28, 2017

Astrid Maute states that accurate magnetic field measurements at ground and Low-Earth Orbit (LEO) are crucial to describe Earth's magnetic field. LEO data is also used to study the ionosphere. One of the challenges with processing LEO magnetic field measurements is that the satellite flies in regions of highly varying ionospheric currents. For scientific studies of Earth's magnetic field it is necessary to characterize accurately the effects of ionospheric current in the LEO data.

 magnetic effect of gravity and plasma pressure gradient
Illustration of approximating the magnetic effect of gravity and plasma pressure gradient driven current at 15 local time (LT) and 20 LT (left and right side panels, respectively): eastward source current density due to gravity and plasma pressure gradient [nA/m2] (1a & 2a), approximation of the magnetic effect of these currents [nT] (1b & 2b), magnetic effect considering the 3D current system which we treat as the "truth" [nt] (1c & 2c), difference between "truth" and approximation indicating the error in the approximation (1d & 2d).

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 which 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 itself. 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 below the peak, in the 300 km to 500 km altitude region, there is a significant height and latitudinal variation of the magnetic signal. During solar minimum the simulations indicate that 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.

Publication Name: Journal of Geophysical Research