Solar wind density and velocity control of auroral brightness under normal interplanetary magnetic field conditions

In this study we determine relationships between auroral brightness and each of the solar wind density and velocity under normal interplanetary magnetic field (IMF) conditions using Polar Lyman-Birge-Hopfield long band (∼170.0 nm) images and Interplanetary Monitoring Platform 8 solar wind data. Since IMF and season are parameters that can affect the auroral brightness, the determination of the relationships is performed on the basis of the IMF B _Z polarity and season to reduce some contamination from these two parameters. It is found that for southward IMF and the winter case the solar wind density and velocity increase the auroral brightness mainly on the nightside. For southward IMF and the summer case the density and velocity also increase the auroral brightness mainly on the nightside, but the increase is not as large as that for southward IMF and the winter case.