## 4 Discussion
It can be seen that the particle transport from \(L\) = 1.2 to 1.15 takes \(\sim\) 20 min for \(E_{\perp}\) = 5 mV/m and \(\sim\)10 min for \(E_{\perp}\) = 10 mV/m. Thus, in the presence of an electric field of 5-10 mV/m, several minutes are enough for the particles to pass further, to the shells L \(\sim\) 1.12-1.13. When the electric pulse is repeated, the particles from these shells will reach the lower 1.05-1.10 shells. In such a multiple pulse scenario, the particles can penetrate deeper and deeper. In addition, during the azimuthal motion, the particles leave the injection region (where the electric field acts) and descend along the shells to lower altitudes. In the case of successive multiple injections (staged), this time \(T\) may be shorter, on the order of several minutes, but then low-energy particles can get into the quasi-trapped zone in several cycles of radial drift over an hour with sporadic \"switching on\" of the driver. The question of the nature and source of the electric field still remains open. The hypothesis of a penetrating large-scale convection electric field could explain the nighttime injections (FEE enhancements), while on the dayside the opposite effect would be observed, with the particles drifting outward. Such penetration of the convection field is possible during the undershielding condition at the night side. The prompt penetrating electric field (PPEF) at the dayside, an alternative, is also associated with southward turning Bz IMF and the dawn-dusk direction of the penetrating electric field, resulting to an outward drift on the dayside. Therefore, large-scale solar wind/magnetospheric penetration electric fields cannot completely solve the problem of low-L injections, particularly at local times other than nighttime. Moreover, from a theoretical point of view, it is difficult to justify a field of several mV/m near the inner edge of ERB and in the forbidden region. It was concluded that none of the global electric field models can describe this penetration field and correctly capture the electric drift or nondiffusive radial transport in the low L-shell region [15; 17]. It should be noted that in the three cases considered, the Bz IMF was directed northward. Hence, in these cases, the large-scale convection electric field decreases and an overshielding effect occurs with a predominance of the dusk-to-dawn electric field. This is inconsistent with the conception of the \"injection--local time\" based on the penetration effect in the night. On the other hand, we have found and demonstrated that abrupt changes in the solar wind pressure, where the dynamic pressure is the main component, might be a more important factor for the low-L injections than the south Bz IMF. An abrupt change in the solar wind pressure affecting the magnetosphere causes a rapid change in the geomagnetic field strength over time \(\partial B/\partial t\). According to [PERSON]'s law of electromagnetic induction rot\(E=-\partial B/\partial t\), an induction electric field arises. As one can see in Table 1, the FEE injection is observed at day when \(\Delta P<0\) acts on the magnetosphere; that is, the magnetosphere expands and the magnetic field decreases \(\partial B/\partial t<0\). Therefore, to provide the daytime inward transport, the transient electric field pulse must be present at lower L with an azimuthal component of large amplitude in the dusk-to-dawn direction. It should be noted that before the decrease of pressure, the size of the magnetosphere is extremely small (see the pressure in Figures 2 and 3), such that the magnetopause can be located inside the geosynchronous orbit [62]. In the high-latitude ionosphere, the whole magnetopause is projected into the small cusp region. Under the strong compression the cusp is shifted to low latitudes. The induction electric field for \(\partial B/\partial t<0\) has a dusk-to-dawn direction at the equatorial boundary of the cusp.