Sorokin, V. M., E. N. Fedorov, A. Yu. Schekotov, O. A. Molchanov, and M. Hayakawa. “Depression of the ULF Geomagnetic Pulsation Related to Ionospheric Irregularities”. Annals of Geophysics, vol. 47, no. 1, Dec. 2004, doi:10.4401/ag-3271.