Probing the link between interplanetary magnetic field directional changes and bow shock geometry using simultaneous Cluster-MMS observations

We compiled a catalogue of 117 simultaneous Cluster-MMS magnetosheath crossings in 2017-2021 (http://www.spacescience.ro/projects/twister). The catalogue includes estimates of bow shock orientation for each event. Assuming that the bow shock normal direction does not change significantly during the magnetosheath crossing duration, we estimate the time evolution of θBn as the angle between the 1-minute time-resolution OMNI interplanetary magnetic field (IMF) and the estimated bow shock normal, and we calculate percentages of quasi-perpendicular (45°< θBn <135°) versus quasi-parallel (0°< θBn <45° or 135°< θBn <180°) bow shock orientations for each magnetosheath crossing. Ideally, if 45°< θBn <135° for the entire set of magnetosheath observations, that crossing would be considered “purely” quasi-perpendicular. Instead, we find that most magnetosheath crossings in our catalogue can be classified as “mixed”, i.e.  the bow shock orientation changes from quasi-perpendicular to quasi-parallel during the event. The assumption that the bow shock normal remains constant, implies that all changes of θBn characterising the mixed events are due to changes of IMF direction. To quantify this, we identify and catalogue IMF directional discontinuities during each event, using the algorithm described in Dumitru and Munteanu (2023) (https://doi.org/10.1029/2023EA002960). We present the results of the discontinuity detection algorithm and we probe the effect/role of IMF directional changes on our estimations of bow shock orientation.