Investigating Anomalies in the Prediction Model for the Dayside Magnetopause Reconnection Location

Several studies have validated the accuracy of the Maximum Magnetic Shear model to predict the location of the reconnection site at the dayside magnetopause. These studies found agreement between model and observations for 74% to 88% of events examined [e.g., Vines et al., 2015; Petrinec et al., 2016; Trattner et al., 2016]. It should be noted that, of the events that failed the prediction of the model, 72% shared a very specific parameter range. These events occurred around equinox and for an IMF clock angle of about 240°. This study investigates this remarkable grouping of events using data from the recently launched MMS mission. Our MMS magnetopause encounter data base, which includes both full and partial magnetopause crossings, contains about 4500 intervals. Those with available solar wind observations are sorted by IMF clock angle to create a data base for the IMF clock angle parameter range between 210° and 260°. Predictions of the reconnection location for events within one month of equinox are compared with predictions for events occurring further from equinox to quantify the anomaly discovered with limited events and data coverage and to document specific local conditions for which location anomalies occurred.