Interplanetary magnetic field B_x asymmetry effect on auroral brightness

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 B_z (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 B _x than for positive B_x under similar B_y conditions when the IMF is southward. This B_x 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 B_x asymmetry is not statistically present in both summer and winter. Recent studies have shown that hemispheric auroral power for negative B_y is higher than that for positive B_y. In summary, hemispheric auroral power reaches its highest level when all the components of the IMF are negative.