Diurnal Variation of Aurora and Geomagnetic Disturbance at New Zealand Antarctic Stations

Abstract

THE diurnal variation of auroral incidence for Scott Base (New Zealand) and Hallett Station (United States–New Zealand) during the International Geophysical Year is shown in Fig. 1A. Curves derived from analyses of concurrent visual and all-sky camera observations are shown separately. The visual curves are based on observations during all hours which have$\frac{3}{8}$or less cloud cover and the all-sky camera curves on photographs in which the Southern Cross is visible (exposures: Scott Base 20 sec, Hallett Station 15 sec, on Tri-X film). The auroral frequencies were computed from quarter-hourly data except Hallett Station visual for which virtually continuous observations were used. This higher density and also the greater sensitivity of the visual observations at Hallett Station for displays near the horizon and in the presence of moonlight, twilight, and thin cloud lift the Hallett visual frequencies well above the photographic frequencies. The Scott Base visual curve is indistinguishable from the one obtained at Cape Evans during 1911, a period of sunspot minimum, by the British (Terra Nova) Antarctic Expedition¹.