Interplanetary magnetic field Bx asymmetry effect on auroral brightness

Abstract

We derive Northern Hemispheric auroral brightness patterns using images from Polar Ultraviolet Imager Lyman‐Birge‐Hopfield long band emissions (∼170.0 nm). Pixels of these images are binned by the X and Y components of the interplanetary magnetic field (IMF) under the combinations of two seasonal (summer and winter) and two IMF Bz (northward and southward) conditions. Hemispheric auroral power is estimated from these images by an integration of auroral brightness over 60°–90° MLAT for all local times. It is found that the hemispheric auroral power is higher for negative Bx than for positive Bx under similar By conditions when the IMF is southward. This Bx asymmetry of the hemispheric auroral power is significant both in summer and winter. For the northward IMF the hemispheric auroral power is low and the Bx asymmetry is not statistically present in both summer and winter. Recent studies have shown that hemispheric auroral power for negative By is higher than that for positive By. In summary, hemispheric auroral power reaches its highest level when all the components of the IMF are negative.