GOES-16 and GOES-17 are the first of NOAA’s Geostationary Operational Environmental Satellite (GOES)-R series of satellites. Each GOES-R satellite has a magnetometer mounted on the end (outboard) and one part-way down a long boom (inboard). This paper demonstrates the relative accuracy and stability of the measurements on a daily and long-term basis. The GOES-16 and GOES-17 magnetic field observations from 2017 to 2020 have been compared to simultaneous magnetic field observations from each other and from the previous GOES-NOP series satellites (GOES-13, GOES-14 and GOES-15). These comparisons provide assessments of relative accuracy and stability. We use a field model to facilitate the inter-satellite comparisons at different longitudes. GOES-16 inboard and outboard magnetometers data suffer daily variations which cannot be explained by natural phenomena. Long-term averaged GOES-16 outboard (OB) data has daily variations of ± 3 nT which are stable within ± 1.5 nT. Long-term averaged GOES-17OB magnetometer data have minimal daily variations (less than ± 1 nT). Daily average of the difference between the GOES-16 outboard or GOES-17 outboard measurements and the measurements made by another GOES satellite are computed. The long-term averaged results show the GOES-16OB and GOES-17OB measurements have long-term stability (± 2 nT or less) and match measurements from magnetometers on other GOES within limits stated herein. The GOES-17OB operational offset (zero field value) was refined using the GOES-17 satellite rotated 180° about the Earth pointing axis (known as a yaw flip).

Deep penetration of energetic electrons (10s-100s of keV) to low L-shells (L<4), as an important source of inner belt electrons, is commonly observed during geomagnetically active times. However, such deep penetration is not observed as frequently for similar energy protons, for which underlying mechanisms are not fully understood. To study their differential deep penetration, we conducted a statistical analysis using phase space densities (PSD) of μ=10-50 MeV/G, K=0.14 G^1/2Re electrons and protons from multi-year Van Allen Probes observations. The results suggest systematic differences in electron and proton deep penetration: electron PSD enhancements at low L-shells occur more frequently, deeply, and faster than protons. For μ=10-50 MeV/G electrons, the occurrence rate of deep penetration events (defined as daily-averaged PSD enhanced by at least a factor of 2 within a day at L<4) is ~2-3 events/month. For protons, only ~1 event/month was observed for μ=10 MeV/G, and much fewer events were identified for μ>20 MeV/G. Leveraging dual-Probe configurations, fast electron deep penetrations at L<4 are revealed: ~70% of electron deep penetration events occurred within ~9 hours; ~8%-13% occurred even within 3 hours, with lower-μ electrons penetrating faster than higher-μ electrons. These results suggest non-diffusive radial transport as the main mechanism of electron deep penetrations. In comparison, proton deep penetration happens at a slower pace. Statistics also show that the electron PSD radial gradient is much steeper than protons prior to deep penetration events, which can be responsible for these differential behaviors of electron and proton deep penetrations.

The event of 8 September 2017 was characterized by the effects of the arrival of two interplanetary coronal mass ejections on September 6th and 7th and a resultant geomagnetic storm. This storm event has been widely studied due to its extreme geo-effectiveness in the global geospace. In the inner magnetosphere, the effects included a distinct intensification of the ring current and a severely eroded plasmasphere. However, little attention has been paid to the role that the observed substorm injections played on the storm-time ring current. Starting at 1209 UT on September 8th, multiple substorm onsets occurred spreading over a wide magnetic local time range on the dawn side. Multiple substorm injections were observed simultaneously at geosynchronous orbit by the Los Alamos National Laboratory satellites and the Geostationary Operational Environmental Satellites, and by both the Exploration of energization and Radiation in Geospace/Arase and the Van Allen Probes missions deep in the inner magnetosphere. Subsequent buildup of the ring current was observed. In this study, we will investigate the role of the substorm injections on the extreme ring current response by numerical simulations with the physics-based Comprehensive Inner Magnetosphere-Ionosphere model using the geosynchronous data as boundary conditions to the model. Since the ring current has a strong influence on the inner magnetospheric dynamics, we also consider its impacts on the dynamics of the electric field and the plasmasphere. Furthermore, this study addresses the critical need to include substorms in evaluating the geo-effectiveness of geomagnetic storms.

Simultaneous bursts of EMIC and longer-period ULF waves were observed by the GOES-16 magnetometer on the 11 January and the 7 September 2017. No correlation was found between the repeat times of EMIC wavepackets and Pc4 ULF wave periods. However, the repetition times visually correlated with variations in solar wind dynamic pressure (Pdyn). EMIC wavepackets are composed of short duration subpackets and when subpackets last >1/2 the ULF wave period, correlation with the ULF wave cycle was strong, R=0.6. On 11 Jan., observations suggest the Pc5 ULF waves were in-part directly driven by Pdyn. The observed Pc4-5 ULF waves were predominately poloidal. Assuming high azimuthal m-numbers, the observations as a whole imply that the simultaneous repeating EMIC and Pc4-5 wave bursts were formed by mode cross-coupling through a common wave generation free energy source of anisotropic ion distributions created by repetitive magnetospheric compressions driven by small Pdyn fluctuations.