[1] To address the mechanism and factors controlling the injection of energetic particles to the geostationary orbit (GEO), we analyzed the appearance of injections at the GEO drift shell as observed by LANL spacecraft in the cases where the flow bursts and associated transient dipolarization were detected at the entry to the inner magnetosphere, in the high beta plasma sheet region on the nightside between 8 and 13 Re. We analyzed two different data sets, one including Geotail observations in 1995-2005 and another including a set of Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations in [2008][2009]. We found that only a small portion of all flow bursts at 8-13 Re were associated with particle injection at GEO but that those injection-associated flows had smaller values of plasma tube entropy parameter (PV 5/3 ) as well as larger change of magnetic field north-south component (dBz). This confirms a scenario that the bursty flows at the entry of the inner magnetosphere (8-13 Re) penetrate into GEO and produce there the energetic particles flux increase. According to the bubble theory of magnetotail plasma flows, the probability of the deep plasma penetration critically depends on how stretched the magnetospheric configuration is, and this dependence is statistically confirmed in a large database to be the major factor controlling the occurrence of GEO injections. We suggest using the background plasma tube entropy value in the nightside part of the GEO drift shell as a suitable parameter to predict the probability of particle injection to GEO. One more outcome of this study is that the energetic particle injections cannot reliably serve as a tool to identify the substorm onset times, as has been done in many past studies.

Key Points:• Flow burst stops where its entropy is nearly equal to entropy of ambient plasma • Flow burst modifies pressure and entropy distribution in the inner magnetosphere • Long relaxation time after the FB subsided provides long-duration SCW effects Supporting Information:• Readme • Figure S1.pdf • Figure S2.pdf • Figure S3.pdf • Figure S4.pdf fortuitously stopped at ∼ 9 Re within a unique, compact multispacecraft constellation for the duration of a 30 min long substorm current wedge-related dipolarization. Observations inside and outside the halted flow burst indicate that it retained properties (including a narrow DF, a localized compression region ahead of it, and its structured, low density, low entropy (pV 5∕3 ) content) when arrived at its stopping point, where the entropy of the ambient plasma was nearly equal to that of the flow burst. We show that even short-duration flow bursts can significantly modify pressure and entropy distributions in the inner magnetosphere. The new distribution takes a long time to relax (a few tens of minutes, consistent with substorm recovery time scales). We argue that these pressure and entropy changes resulting from the incoming flow bursts can be responsible for the support/generation of a substorm current wedge.

Abstract. Data from a cluster of three THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft during February-March 2009 frequently provide an opportunity to construct local data-adaptive magnetospheric models, which are suitable for the accurate mapping along the magnetic field lines at distances of 6-9 Re in the nightside magnetosphere. This allows us to map the isotropy boundaries (IBs) of 30 and 80 keV protons observed by low-altitude NOAA POES (Polar Orbiting Environmental Satellites) to the equatorial magnetosphere (to find the projected isotropy boundary, PIB) and study the magnetospheric conditions, particularly to evaluate the ratio K IB (R c /r c ; the magnetic field curvature radius to the particle gyroradius) in the neutral sheet at that point. Special care is taken to control the factors which influence the accuracy of the adaptive models and mapping. Data indicate that better accuracy of an adaptive model is achieved when the PIB distance from the closest spacecraft is as small as 1-2 Re. For this group of most accurate predictions, the spread of K IB values is still large (from 4 to 32), with the median value K IB ∼ 13 being larger than the critical value K cr ∼ 8 expected at the inner boundary of nonadiabatic angular scattering in the current sheet. It appears that two different mechanisms may contribute to form the isotropy boundary. The group with K ∼ [4, 12] is most likely formed by current sheet scattering, whereas the group having K IB ∼ [12, 32] could be formed by the resonant scattering of low-energy protons by the electromagnetic ion-cyclotron (EMIC) waves. The energy dependence of the upper K limit and close proximity of the latter event to the plasmapause locations support this conclusion.We also discuss other reasons why the K ∼ 8 criterion for isotropization may fail to work, as well as a possible relationship between the two scattering mechanisms.

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