The dependence of winter aurora on interplanetary parameters

Abstract

The dependence of the northern winter aurora on interplanetary parameters is examined for images obtained from the Polar spacecraft Ultraviolet Imager (UVI) during the month of January 1997. Linear correlation analysis is used to relate auroral brightness to interplanetary parameters as a function of magnetic latitude (MLAT) and magnetic local time (MLT). Spatial maps of maximum magnitude correlation coefficient and optimal lag times are presented. In addition, the Method of Natural Orthogonal Components (MNOC) is applied to UVI images and an orthogonal set of eigenmodes of auroral behavior is produced. The dominant eigenmodes are determined to be (1) the main auroral oval brightness, (2) polar cap contraction/expansion, (3) dawn/dusk aurora, and (4) midnight sector brightening/quenching. The temporal coefficients for the various eigenmodes are correlated separately with solar wind parameters and interplanetary magnetic field (IMF) components. The dominant influence of the negative Bz component is confirmed, but the timescale of its influence is found to vary widely. The MNOC procedure allows some of the more subtle relationships between the aurora and the interplanetary parameters to be isolated, particularly those associated with the solar wind density and IMF Bx and By.