EMVIM: An empirical model for the magnetic field configuration near Venus

Abstract

More than 2000 orbits of Venus Express magnetic field measurements are condensed into Empirical Model of Venusian Induced Magnetic fields (EMVIM), an empirical model to quantify the magnetic configuration in the Venusian magnetosphere at low altitude (<500 km) as a function of the upstream solar wind magnetic field (IMF components) and the solar activity index F_10.7 as control variables. Empirical orthogonal function (EOF) analysis is used to construct a set of data-derived basis functions that are associated with different fundamental magnetospheric processes. The most important basis function represents the magnetic draping configuration of the IMFz component while the second important one represents the draping of the IMFy component. Solar wind-magnetosphere interactions are quantified through regression analysis of EOF amplitudes and the control variables. Combining the basis functions with regression coefficients results in a model with a determination coefficient R² of 0.29. As an applicational example, the model is used to quantify the density of the terminator end of the tail current J_E in terms of cross-flow IMF component and F_10.7 as JE_A/ṡkm^-1 = 3.75ṡ(IMF_⊥+0.264 nT/nT-0.0190ṡ(IMF_⊥ṡF_10.7+30.3 nTṡsolar flux unit (1 sfu = 10^-22 W m^-2 Hz^-1))/nTṡsfu -0.00182ṡ(F_10.7²-7237 sfu²)/sfu², showing that the current strength is anticorrelated with solar activity.