Magnetosonic ULF Waves With Anomalous Plasma–Magnetic Field Correlations: Standing Waves and Inhomogeneous Plasmas

Abstract Ultra‐low frequency (ULF) wave observations across the heliosphere often rely on sign of correlations between plasma (density/pressure) and magnetic field perturbations to distinguish fast slow magnetosonic modes. However, assumptions behind this magnetohydrodynamic result are not always valid, particularly within magnetosphere which is inhomogeneous supports standing waves along geomagnetic field. Through theory a global simulation, we find both effects can in anomalous plasma–magnetic correlations. The interference pattern lead body surface have different cross‐phases than their constituent propagating waves. Furthermore, if scale gradients background shorter wavelength or near‐incompressible, then advection by inhomogeneities overcome wave's inherent sense compression. These need be allowed for taken into account when applying typical diagnostic observations.