LIS and modulated GCR spectra derived from the force-field approximation. The LIS from Corti et al. (2019b) is shown as a thin black line, with the shaded gray area representing the uncertainty range encompassing three standard deviations. The thick colored lines represent the GCR spectra near 1 AU, calculated using the force-field approximation under different solar modulation potentials. Markers indicate measurements from AMS-02, SOHO/EPHIN, and IMP-8 during different time periods with very similar modulation conditions. In some cases (particularly IMP-8 and AMS-02) vertical bars showing the measurement uncertainties are too small to be seen. The data point with the lowest energy for IMP8 originates from CRNC; it is included in this figure solely for display purposes and is not used in this study. More information about the observational data is listed in Table 1.