Investigating a Solar Wind Stream Interaction Region using Interplanetary Spacecraft Radio Signals: A Magnetohydrodynamic Simulation Study

Stream interaction regions (SIRs) are spiral heliospheric structures that arise at the interface between fast and preceding slow solar wind regions. SIR enhancements of density and magnetic field intensity, often with magnetic polarity inversion, are potentially geoeffective and therefore important in the analysis of space weather. We studied an MHD heliospheric simulation containing a well-defined SIR using a new instrument concept based on trans-heliospheric radio sensing: Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH). FETCH uses line-of-sight radio propagation techniques to measure Faraday rotation and electron column density. Analysis of the simulated FETCH observations clearly demonstrated density and magnetic field enhancements, and magnetic polarity reversal, all of which were confirmed in Wind spacecraft measurements at 1 au. FETCH provided 4.5-5.7 days lead times for predicting the arrival of SIR features at Earth. The SIR radial speed was estimated to be 350-390 km s^-1. These initial results hold promise that FETCH will be valuable in detecting and characterizing the inner heliosphere SIR properties well ahead of their presentation in the local geospace environment.