Proton anisotropy in velocity space has been generally accepted as a major parameter for exciting electromagnetic ion cyclotron (EMIC) waves. In this study, we estimate the proton anisotropy parameter as defined by the linear resonance theory using data from the Van Allen Probes mission. Our investigation uses the measurements of the inner magnetosphere (L < 6) from January 2013 to February 2018. We find that the proton anisotropy is always clearly limited by an upper bound and it well follows an inverse relationship with the parallel proton b (the ratio of the plasma pressure to the magnetic pressure) within a certain range. This upper bound exists over wide spatial regions, AE conditions, and resonance energies regardless of the presence of EMIC waves. EMIC waves occur when the anisotropy lies below but close to this upper bound within a narrow plasma b range: The lower cutoff b is due to an excessively high anisotropy threshold and the upper cutoff b is possibly due to the predominant role of a faster-growing mirror mode instability. We also find that the anisotropy during the observed EMIC waves is unstable, leading to the linear ion cyclotron instability. This result implies that the upper bound of the anisotropy is due to nonlinear processes.

Nearly all studies of impulsive magnetic perturbation events (MPEs) with large magnetic field variability (dB/dt) that can produce dangerous geomagnetically-induced currents (GICs) have used data from the northern hemisphere. Here we present details of four large-amplitude MPE events (|DBx|> 900 nT and |dB/dt| > 10 nT/s in at least one component) observed between 2015 and 2018 in conjugate high latitude regions (65 - 80° corrected geomagnetic latitude), using magnetometer data from (1) Pangnirtung and Iqaluit in eastern Arctic Canada and the magnetically conjugate South Pole Station in Antarctica and (2) the Greenland West Coast Chain and two magnetically conjugate chains in Antarctica, AAL-PIP and BAS LPM. From 1 to 3 different isolated MPEs localized in corrected geomagnetic latitude were observed during 3 pre-midnight events; many were simultaneous within 3 min in both hemispheres. Their conjugate latitudinal amplitude profiles, however, matched qualitatively at best. During an extended post-midnight interval, which we associate with an interval of omega bands, multiple highly localized MPEs occurred independently in time at each station in both hemispheres. These nighttime MPEs occurred under a wide range of geomagnetic conditions, but common to each was a negative IMF Bz that exhibited at least a modest increase at or near the time of the event. A comparison of perturbation amplitudes to modeled ionospheric conductivities in conjugate hemispheres clearly favored a current generator model over a voltage generator model for 3 of the 4 events; neither model provided a good fit for the pre-midnight event that occurred near vernal equinox.

Understanding the dynamical behavior of plasma and energetic particles in Earth’s inner magnetosphere requires carefully designed and calibrated instrumentation. The Van Allen Probes Mission included two instruments capable of measuring the proton distribution function in-situ. The Energetic Particle Composition and Thermal Plasma Suite (ECT) – Helium Oxygen, Proton, and Electron (HOPE) spectrometer (Spence et al., 2013; Funsten et al., 2013) used a top-hat detector designed to measure protons from the SC potential through 50 KeV in logarithmic energy steps. The Radiation Belt Storm Probes Ion Composition Detector (RBSPICE) instrument (Mitchell, 2013) used a time of flight and SSD detector design to measure protons from approximately 7 KeV through 650 KeV in logarithmic energy steps. Using the overlap of energy channels between the two instruments, the two instrument teams have worked diligently during the final Phase F of the mission to calibrate the observations so that a continuous distribution function can be resolved on nearly a spin-by-spin basis. During the life of these two instruments calibration changes have been required both on-board the spacecraft as well as within the final production datasets. Manweiler (2018) provided an early report on the intercalibration factors between HOPE and RBSPICE with a nominal factor of two difference between the proton data sets in the energy range between 7 and 50 KeV. With the final production of each of these data sets occurring in Fall 2021, both teams have been worked together to provide for an understanding of the required intercalibration factors to be used so that a full distribution function is available on a spin-by-spin basis. In this poster we report on the final efforts to provide this calibrated set of data products between the two instruments. Details of the intercalibration calculations are presented as well as year by year L by MLT maps of the factors required to match both datasets. Finally, we report on a supplementary data set that is to be made available which contains the spin-by-spin factors required to match the ECT/HOPE and RBSPICE/TOFxPH proton datasets. Funsten, H.O., et al. Space Sci Rev 179, 2013 Manweiler, J. W., et al., 2018 GEM Summer Workshop. Mitchell, D.G., et al., Space Sci. Rev., 179, 2013 Spence, H.E., et al. Space Sci Rev 179, 2013

Nearly all studies of impulsive magnetic perturbation events (MPEs) that can produce dangerous geomagnetically induced currents (GICs) have used data from the northern hemisphere. In this study we investigated MPE occurrences during the first 6 months of 2016 at four magnetically conjugate high latitude station pairs using data from the Greenland West Coast magnetometer chain and from Antarctic stations in the conjugate AAL-PIP magnetometer chain. Events for statistical analysis and four case studies were selected from Greenland/AAL-PIP data by detecting the presence of >6 nT/s derivatives of any component of the magnetic field at any of the station pairs. For case studies, these chains were supplemented by data from the BAS-LPM chain in Antarctica as well as Pangnirtung and South Pole in order to extend longitudinal coverage to the west. Amplitude comparisons between hemispheres showed a) a seasonal dependence (larger in the winter hemisphere), and b) a dependence on the sign of the By component of the interplanetary magnetic field (IMF): MPEs were larger in the north (south) when IMF By was > 0 (< 0). A majority of events occurred nearly simultaneously (to within ± 3 min) independent of the sign of By as long as |By| ≤ 2 |Bz|. As has been found in earlier studies, IMF Bz was < 0 prior to most events. When IMF data from Geotail, Themis-B, and/or Themis C in the near-Earth solar wind were used to supplement the time-shifted OMNI IMF data, the consistency of these IMF orientations was improved.