VERTICAL EXTENT OF AURORAL ARCS AND BANDS

Abstract

Measurements of the vertical extent of quiet arcs and bands from 181 auroral photographs, taken at Chesterfield (63.3 °N., 90.7 °W.), Coppermine (67.8 °N., 115.2 °W.), and Saskatoon (52.1 °N., 106.6 °W.), indicate that these forms are confined to a narrow layer of the atmosphere immediately above the 100-km. level. The most frequent thickness of this layer is between 20 and 40 km. Values in excess of 50 km. rarely occur. The percentage of auroral time that the luminosity is restricted to this layer is uncertain. The ratio of the number of arcs and bands to the total number of observed forms suggests a value exceeding 50%. When the occurrence of each form is weighted according to the angular field covered by it, a value as high as 60% is indicated.