NocturnalEsionization and “no echo” occurrences, as recorded onh′frecords, have been classified according to the absence or presence of aurora and to its form when present in the zenith areas. The analysis supports the following generalizations. (1)Esionization increases at successively greater heights as aurora approaches the College zenith from the north. (2) In the presence of different nonpulsating auroral forms theEsionization varies with changes in auroral form in a manner similar to the change in luminosity. Likewise, variations in the height of maximum ionization parallel variations in auroral heights. (3) Complete absorption is only slightly more frequent during non‐pulsating aurora than during absence of aurora but prevails in the presence of pulsating aurora. Geomagnetic relationships are di