AIRBORNE OBSERVATION OF MIDDAY AURORA

On December 13, 1967, a KC-135 aircraft equipped with an ionospheric sounder, a photometer, and an all-sky camera made a flight into the midday portion of the auroral oval and the polar cap region between Greenland and Spitzbergen. Under the quiet magnetic conditions (ΣKp = 10 -) occurring on that day, tho midday aurora consisted of a single arc which lay within the expected region of the oval. The aurora was absent inside the oval. There was a strong correlation between auroral Es and visible overhead aurora. Near the end of the flight when sunrise prevented optical observations of the aurora, the observed occurrence of Es was used to infer the width of the auroral oval. © 1969.