One-Dimensional Upward Continuation of the Ground Magnetic Field Using Spherical Elementary Current Systems

The method of spherical elementary current systems (SECS) has been successfully applied to derive ionospheric equivalent currents from ground magnetometer data. Its one-dimensional variant (1D SECS) is now introduced especially for situations with data available only from a chain of magnetometers. We compare equivalent currents obtained by the 2D and 1D SECS methods and by 1D Fourier method using synthetic 1D current models. Then we study real situations with data from a 2D (IMAGE) and 1D (MM210) magnetometer network. We show that the 1D SECS reveals the integrated eastward and westward current densities very reasonably compared to the 2D SECS, also during clearly non-1D situations. It also follows that the 1D SECS can be applied in a routine manner to replace the commonly used local electrojet proxies (local AL and AU indices) by a direct quantitative estimate of the ionospheric currents.