TY - RPRT TI - Mean electron density variations of the quiet ionosphere no. 12 AU - Brown, DJ AU - Wescott, LR AU - Wright, J W PY - 1960 PB - National Bureau of Standards CY - Gaithersburg, MD SN - NBS TN 40-12 DO - 10.6028/NBS.TN.40-12 ER -