[1] Electromagnetic ion cyclotron waves at high L values near local noon are often found to be related to magnetospheric compression events. These waves arise from temperature anisotropies in trapped warm plasma populations. There are several possible mechanisms that can generate these temperature anisotropies, including both energizing and nonenergizing processes. In this work we investigate a nonenergizing process arising from dayside bifurcated magnetic field minima. There are two kinds of behavior particles undergo in the presence of bifurcated minima: particles with high initial equatorial pitch angles (EPAs) are forced to execute so-called Shabansky orbits and mirror at high latitudes without passing through the equator, while those with lower initial EPAs will pass through the equator with higher EPAs than before; as a result, perpendicular energies near the equator increase at the cost of parallel energies. By using a 3-D particle tracing code in a tunable analytic compressed-dipole field, we explore the effects of Shabansky orbits on the anisotropy of the warm plasma and contrast with the anisotropy resulting from drift shell splitting. We show that Shabansky orbits are an independent source of temperature anisotropy for warm dayside ions.

electromagnetic ion cyclotron (EMIC) waves were observed on the ground by the Canadian Array for Realtime Investigations of Magnetic Activity (CARISMA) network of magnetometers between L = 4 and L = 6 in response to a significant magnetospheric compression. Here a new MHD/particle method for studying EMIC wave growth in the magnetosphere is used to provide a detailed study of the compression event. We compare equatorial field line crossings of NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and CARISMA observation sites to frequency-integrated wave growth rates from the MHD/particle method. Simulated temperatures were constant in time, suggesting an absence of energizing processes during this event. Many particles experienced so-called Shabansky orbits during this event, in which their drift motion was confined to high latitudes in the dayside magnetosphere. We propose a new nonenergizing process, driven by ions undergoing Shabansky orbits, for generating ion temperature anisotropies. In addition, the fundamental role of the plasmasphere in generating EMIC waves from the free energy of warm ion temperature anisotropies is discussed.

Geomagnetic indices are convenient quantities that distill the complicated physics of some region or aspect of near‐Earth space into a single parameter. Most of the best‐known indices are calculated from ground‐based magnetometer data sets, such as Dst, SYM‐H, Kp, AE, AL, and PC. Many models have been created that predict the values of these indices, often using solar wind measurements upstream from Earth as the input variables to the calculation. This document reviews the current state of models that predict geomagnetic indices and the methods used to assess their ability to reproduce the target index time series. These existing methods are synthesized into a baseline collection of metrics for benchmarking a new or updated geomagnetic index prediction model. These methods fall into two categories: (1) fit performance metrics such as root‐mean‐square error and mean absolute error that are applied to a time series comparison of model output and observations and (2) event detection performance metrics such as Heidke Skill Score and probability of detection that are derived from a contingency table that compares model and observation values exceeding (or not) a threshold value. A few examples of codes being used with this set of metrics are presented, and other aspects of metrics assessment best practices, limitations, and uncertainties are discussed, including several caveats to consider when using geomagnetic indices.