J. Liu, T. Nakamura, L. Liu, W. Wang, N. Balan, T. Nishiyama, M. R. Hairston, and E. G. Thomas. Formation of polar ionospheric tongue of ionization during minor geomagnetic disturbed conditions. J. Geophys. Res., volume 120, issue 8, pages 6860-6873, 2015 .