Substorms can be identified from negative bays in the AL/SML index, which traces the minimum northward ground magnetic deflection at auroral latitudes, produced by enhancements of the westward electrojet. For substorms, negative bays are caused by the closure of the Substorm Current Wedge through the ionosphere, typically localised to the nightside and centred around 23-00 magnetic local time (MLT). In this case, the equivalent current pattern that causes the magnetic deflections is given the name Disturbance Polar (DP) 1. However, negative bays may also form when the westward electrojet is enhanced by increased convection, driving Pedersen and Hall currents in the auroral zone. Convection enhancements also strengthen the eastward electrojet, monitored by the maximum northward ground magnetic deflection as the AU/SMU index. In this case, the equivalent current pattern that produces the magnetic deflections is called DP2. Unlike other substorm identification methods, the SOPHIE method by Forsyth et al. (2015) attempts to distinguish between the DP1 and DP2 enhancements that cause substorm-like SML bays by also examining the SMU index. Despite this, we find evidence that up to 59% of the 30329 events originally identified as substorms come from enhancements of DP2 on top of the 2627 convection enhancement events already identified between 1997 and 2020. We explore ways to improve substorm identification using auroral indices to fully separate the DP1 and DP2 bays, but conclude that there is insufficient information in the auroral indices alone to achieve this.

Earth’s inner magnetosphere contains multiple electron populations influenced by different factors. The cold electrons of the plasmasphere, warm plasma that contributes to the ring current, and the relativistic plasma of the radiation belt often seem to behave independently. Using omni-directional flux and energy measurements from the HOPE and MagEIS instruments aboard the Van Allen Probes, we provide a detailed density and temperature description of the inner magnetosphere, offering a comprehensive statistical analysis of the entire Van Allen Probe era. While number density and temperature data at geosynchronous orbit are available, this study focuses on the inner magnetosphere (2 < L∗ < 6). Values of density and temperature are extracted by fitting energy and phase space density to obtain the distribution function. The fitted distributions are related to the zeroth and second moments to estimate the number density and temperature. Analysis has indicated that a two Maxwellian fit is sufficient over a wide range of L∗ and that there are two independent plasma populations. The more energetic population has a median number density of approximately 1.2 × 104 m−3 and a temperature of around 130 keV, with a temperature peak observed between L* = 4 and L*= 4.5. This population is relatively uniform in MLT. In contrast, the less energetic warm electron population has a median number density of about 2.5 × 104 m−3 and a temperature of 7.4 keV. Strong statistical trends in density and temperature across both L* and MLT are presented, along with potential sources driving these variations.