Variability in Footpoint Mapping of BBFs Using Tsyganenko Models: Impact on Swarm Conjunctions

Abstract

Magnetospheric-ionospheric coupling studies often rely on multi-spacecraft conjunctions, which require accurate magnetic field mapping tools. For example, linking measurements from the magnetotail with those in the ionosphere involves determining when the orbital magnetic footpoint of THEMIS or MMS intersects with the footpoint of Swarm. One of the most commonly used tools for tracing magnetic field lines are the Tsyganenko models. In this study, we aim to analyze how the footpoint locations are impacted by the inputs parameters of these models, including solar wind conditions, geomagnetic activity, and the location in the magnetotail. A dataset of 2394 bursty bulk flows (BBFs) detected by MMS was mapped to Earth's ionosphere with four different Tsyganenko models. The MLT position showed a variability of approximately +/-1 MLT across the models. Footpoint locations were linked to the dawn-dusk position of the BBFs, with differences between models associated with variations in the interplanetary magnetic field clock angle. The MLAT values exhibited greater variability of approximately +/-2{\deg} around the mean value, with a systematic shift toward higher latitudes observed in two of the four models. This position is also influenced by the the input parameter of the model representing the dynamics of Earth's magnetosphere, with larger values corresponding to lower latitudes. The uncertainty on the footpoint location impacts the number of conjunctions. Generally, Swarm B exhibited more conjunctions than Swarm A or C in the northern hemisphere, and less than half of these conjunctions had Tsyganenko footpoint distances below the typical BBF footprint size in the ionosphere.