Very low brightness fluctuations in the mid-latitude aurora

Abstract

From ground-based photometric observations made near Dunedin, New Zealand, at L = 2.71, weak mid-latitude electron precipitation is detected through the appearance of a characteristic signature in the cross correlogram of λ3914 and λ5577 brightness fluctuations. The method is sufficiently sensitive to detect rms brightness fluctuations at 3914 Å, σ(Bv), as low as 0.03 R in an observing time of several minutes. During magnetically quiet periods with Kp ≤ 3 we observe that σ(Bv), on a time scale of seconds, falls below this limit, which corresponds to a precipitating electron flux of ∼200 el cm−2 s−1 sr−1 at 40 keV providing σ(Bv) ∼ (Bv). For Kp ≥ 5, there is an approximate increase of 5.6 in flux magnitude per unit Kp.