## 6 Conclusions  
The study of geomagnetic storms and other space weather phenomena is crucial to better understand the mechanisms taking place during solar events and to prevent their effects on technological and anthropic systems, such as reduced satellite operations, failures in spacecraft electronics, radio communication problems, etc. On 25 August 2018, the CSES-01/HEPD particle rate meters were able to detect the effects of a G3-class, ICME-driven geomagnetic disturbance characterized by marked magnetosphere compression and plasmasphere erosion. In our analysis, a depletion of HEPD count rate at the storm's main phase was observed, followed by a clear rate enhancement during its recovery phase. This increase was detected at L-shells \(\gtrsim\)3 for electron energies above 3 MeV, and, to a lesser extent, at L-shells \(\gtrsim\)4 for electron energies above 4.5 MeV. These results were consistent with the behavior of integral sub-MeV fluxes measured by the MEPED-90\({}^{\circ}\) electron telescope on board the NOAA19/POES satellite, over the same period. The enhancement of HEPD trigger rates suggested a phenomenon of acceleration of energetic electrons, which lasted several days. The discrimination between adiabatic radial transport and non-adiabatic local heating was made by inspection of the PSD profiles of the REPT magnetospheric  
Figure 9: Radial PSD profiles at constant \(\mu\) (4500 \(\frac{MeV}{G}\)) and \(K\) (0.1 \(R_{E}G^{\frac{1}{2}}\)) for R8 BP-A/REPT electrons of energies between approximately 3 MeV and 7 MeV along both inbound and outbound crossings of the radiation belts. Complementary R8 BP-B/REPT profiles (not shown) are consistent with their A counterpart. electrons from late 26 August to early 30 August, whose negative gradients were in favour of the latter, with corroboration by persistent chorus wave interactions previously revealed by other payloads on board the CSES-01 for the same storm. During the recovery phase, the HEPD trigger rate enhancement was in coincidence with prolonged and intense substorm activity (\(>\) 1000 nT), as measured by the AL index. This followed the HEPD orbits crossing the auroral oval region, which expanded during the storm and was marked by UV enhancement especially in the Southern Hemisphere, as detected by the SSUSI instrument on board the DMSP satellite. This occurrence showed that auroral processes cannot be neglected when studying the dynamics of particle acceleration in the ORB, since energetic electrons undergo quick acceleration on typical timescales of auroral substorms. Considering the sky-rocketing focus on space weather studies in this last decade, HEPD's results prove promising, especially in view of the already-planned constellation of CSES satellites in the next few years (CSES-02 is currently under construction). It is worth noticing that this set of satellites will take shape in a period when several other missions, which contributed to the monitoring of the near-Earth environment, will be either deactivated or well beyond the end of their scheduled lifetimes. Writing--original draft, F.P. ([PERSON]); conceptualization, M.M. ([PERSON]), M.P. ([PERSON]), and R.S. ; writing--review and editing, A.S., A.P., M.M. ([PERSON]), M.P. ([PERSON]), F.M.F., R.I., A.O., E.R., and R.S. ; designing the experiment or calibration or data production and processing, A.S., A.P., S.B., R.B., W.J.B., D.C., L.C. ([PERSON]), G.C., L.C. ([PERSON]), A.C., G.D., C.D.D., C.D.S., F.M.F., R.I., I.L., N.M., G.M., M.M. ([PERSON]), A.O., G.O., F.P. ([PERSON]), B.P., F.P. ([PERSON]), P.P., M.P. ([PERSON]), E.R., M.R., S.B.R., Z.S., V.S., V.V., S.Z., and P.Z. All authors read and agreed to the published version of the manuscript. This research received no external funding. This research received no external funding. Not applicable. Not applicable. Not applicable. Data Availability Statement: CSES/HEPD data can be found at www.leos.ac.cn/ (accessed on 3 April 2021).