The evolution of the radiation belts in L‐shell (L), energy (E), and equatorial pitch angle (α0) is analyzed during the calm 11‐day interval (4–15 March) following the 1 March 2013 storm. Magnetic Electron and Ion Spectrometer (MagEIS) observations from Van Allen Probes are interpreted alongside 1D and 3D Fokker‐Planck simulations combined with consistent event‐driven scattering modeling from whistler mode hiss waves. Three (L, E, α0) regions persist through 11 days of hiss wave scattering; the pitch angle‐dependent inner belt core (L ~ <2.2 and E < 700 keV), pitch angle homogeneous outer belt low‐energy core (L > ~5 and E~ < 100 keV), and a distinct pocket of electrons (L ~ [4.5, 5.5] and E ~ [0.7, 2] MeV). The pitch angle homogeneous outer belt is explained by the diffusion coefficients that are roughly constant for α0 ~ <60°, E > 100 keV, 3.5 < L < Lpp ~ 6. Thus, observed unidirectional flux decays can be used to estimate local pitch angle diffusion rates in that region. Top‐hat distributions are computed and observed at L ~ 3–3.5 and E = 100–300 keV.

Abstract. We present here plasma data from the Polar HYDRA instrument giving comprehensive coverage of the inner magnetospheric region from L • 2 outward. Data is projected to an equatorial reference plane yielding a global view of the inner extend of the plasma sheet. We determine the inner boundary for plasma sheet electrons and ions in the/• range 0.05 -50 eV nT -• and we compare these to the predicted Alfvfin boundaries as a function of the geomagnetic activity index Kp. In general, the simple conventional drift paradigm is shown to be globally consistent with the averaged data in the inner magnetosphere, with electrons adhering better to the predicted boundaries than ions. The data are further compared to the geosynchronous slice as measured by the Los Alamos Magnetospheric Plasma Analyzer (MPA) which measures the crossing point of the Alfv•n boundaries at geosynchronous altitudes with much better statistical resolution than Polar. Integral to the drift model used is an assumption about the form of the global electric field. The agreement with data validates the simple corotation and convection electric field used and shows that this model describes well the average transport for a wide range of geomagnetic activity and over a large part of the inner magnetosphere.

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The tens of kiloelectron volt ions observed in the ring current region at L ~ 3–7 generally have pancake pitch angle distributions, that is, peaked at 90°. However, in this study, by using the Van Allen Probe observations on the dayside, unexpectedly, we have found that about 5% time, protons with energies of ~30 to 50 keV show two distinct populations, having an additional field‐aligned population overlapping with the original pancake population. The newly appearing field‐aligned populations have higher occurrence rates at ~12–16 magnetic local time during geomagnetically active times. In particular, we have studied eight such events in detail and found that the source regions are located around 12 to 18 magnetic local time which coincides with our statistical result. Based on the ionospheric and geosynchronous observations, it is suggested that these energetic ions with field‐aligned pitch angle distributions probably are accelerated near postnoon in association with ionospheric disturbances that are triggered by tail injections.