Statistical comparison of WINDII auroral green line emission rate with DMSP/SSJ4 electron energy input for high and low solar flux years

Abstract

[1] The atmospheric response to precipitating auroral electrons under varying conditions of solar illumination is investigated using a statistical approach with respect to magnetic local time (MLT), solar zenith angle (χ), and geomagnetic latitude (MLAT) in the northern high-latitude region. Vertical profiles of daytime auroral O(1S) emission rate are obtained from UARS/WINDII measurements by removing the airglow components. These are compared with precipitating electron and proton input observed with DMSP-F10 and -F12 SSJ4 from which total energy and average energy are obtained. In order to investigate the solar flux effect, 2 a of data are examined, 1993 (high solar flux) and 1996 (low solar flux). Total electron energy flux increases with increasing solar zenith angle from 40° to 160° so that the energy flux during nighttime is much greater than in the daytime. During the daytime (χ ≤ 90°) the auroral atmospheric response correlates well with electron energy input yielding auroral production rates of 1.2 and 1.6 kR erg−1 cm2 s, but this relation breaks down beyond χ = 90°. It is suspected that nighttime thin sheet auroral profiles are not correctly inverted for this limb-viewing imager. A strong anticorrelation is found between the altitude of peak auroral volume emission rate and the average precipitating electron energy with slopes of 12.1 km keV−1 and 5.7 km keV−1 for 1993 and 1996, respectively. The dependence of auroral emission rate on solar illumination conditions is consistent with earlier work by Newell et al. (1996b) and others, but the clear dependence on solar zenith angle has not been demonstrated before.