EOF Analysis and Modeling of Venus Express Magnetic Field Measurements at Low Altitudes

Abstract:

Venus Express magnetic field measurements of more than 2000 orbits are collected to study the magnetic environment near Venus at solar minimum. We focus on the magnetic variation at low altitude within a spherical cap centering at the orbit periapsis, using Empirical Orthogonal Function (EOF) analysis and multivariate analysis methods. Investigation illustrates that the most important four EOF basis functions contribute to about 70% of the total variance, and represent the basic variation patterns: EOF1 represents the poloidal draping configuration, EOF2 presents the toroidal draping configuration for a single sheet structure, EOF3 presents the profile of magnetic y-component in the positive motional electric field (+E) Hemisphere, EOF4 represents a double sheet pattern. Regressions reveal the dependency of the magnetic patterns on the interplanetary magnetic field (IMF) components and the VEX orbital orientation, capturing important physical drivers of current systems around Venus. Our study yields a regional magnetic field distribution as a function of IMF, allowing an estimate of regional current.