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. 2022 Apr 28;218(4):22. doi: 10.1007/s11214-022-00890-7

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© The Author(s) 2022

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Fig. 11 — Radial gradients of PSP/ISOIS helium as a function of energy. Data were taken from $\sim 2018.7$ to $\sim 2019.9$ using the LET1 and HET B telescopes on the EPI-Hi sensor. After subtracting solar energetic particle events and de-trending from long-term changes in solar modulation (using SOHO/EPHIN as a 1-AU baseline; see Fig. 10a), fits were applied to 3 forms of data: (i) averaged over Carrington longitudes in the spacecraft frame (Carrington Ave.), (ii) averaged over daily time scales (Daily Ave.), and (iii) averaged in 0.01 AU radial increments (0.01-AU bins). The results for (ii) and (iii) are mostly consistent with each other, while a possibly larger gradient is evident in (i), for which variations caused by solar wind streams have been minimized. The fluxes used in this analysis reflect the combined contribution from all sources at a given energy (e.g., ACRs dominate but the GCRs have not yet been subtracted). Figure from Rankin et al. (2021)