Application and validation of the spherical elementary currents systems technique for deriving ionospheric equivalent currents with the North American and Greenland ground magnetometer arrays

With data from the Canadian Magnetic Observatory System, Canadian Array for Real time Investigations of Magnetic Activity, Geophysical Institute Magnetometer Array, Greenland, Time History of Events and Macroscale Interactions during Substorms (THEMIS), and Magnetometer Array for Cusp and Cleft Studies ground magnetometer arrays, we applied the state-of-art technique on the basis of spherical elementary currents systems (SECS) developed by Amm and Viljanen (1999) in order to calculate maps of ionospheric equivalent currents over the whole North American auroral region. This study is the first to apply the SECS technique to a large nonrectangular area with widely separated ground magnetometers (similar to 350 km). For this study we will first demonstrate the validity of the technique using synthetic data and then examine equivalent ionospheric currents associated with a Harang discontinuity for a case study on 10 December 2007. The results show in detail the dynamic evolution of the currents over the entire North American ground magnetometer network. Equivalent ionospheric current (EIC) maps inferred at the minimum resolution of the database, in this case 10 s, can thus be analyzed further in conjunction with near-simultaneous images of the THEMIS all-sky imager mosaics and Super Dual Auroral Radar Network radar data. The EIC maps represent a value-added product from the raw magnetometer database and can be used for contextual interpretation as well as help with our understanding of magnetosphere-ionosphere coupling mechanisms using the ground arrays and the THEMIS spacecraft data.