Fig. 2
From: Determining polar ionospheric electrojet currents from Swarm satellite constellation magnetic data
Top row shows observations, \(\delta F\), in green along with the model predictions, \(\delta F^{{\mathrm{mod}}}\), for three solution methods, \(L_1\) norm (black), \(L_2\) norm (red), and \(L_2\) norm without Huber-weighted misfit (blue). The middle row shows the model residuals, \(\Delta \delta F\), for the same inversion methods, and the bottom row shows the corresponding sheet current densities, J, again for all three methods. Data are from satellite Alpha for 2 days: (left column) orbit 6248 on 04.01.2015 13:36 to 14:01 UT, corresponding to a magnetic local time (MLT) of midnight around \(60^\circ\) magnetic latitude (disturbed, Kp \(=4^-\)) and (right column) orbit 6493 on 20.01.2015 12:37 to 13:02 UT, a similar MLT (quiet, Kp \(=0^+\)). The sheet current densities are found using \(\alpha ^2 = 6.4\cdot 10^{-15} \frac{\text {nT}^2}{\text {A}}\) for the \(L_1\) norm solution and \(\alpha ^2 = 3.6\cdot 10^{-27} \frac{\text {nT}^2}{\text {A}^2}\) for the \(L_2\) norm solutions. A positive current flows from midnight to noon (sunward)