Quantitative assessment of protons during the solar proton events of September 2017

Abstract We present multi-spacecraft observations of the proton fluxes spanning from 1.5-433 MeV for the largest solar proton event of solar cycle 24, i.e. 7 and 10 September 2017. In September 2017, M5.5 flare on 4 September, X9.3 flare on 6 September and X8.2 flare on 10 September gave rise to solar proton event when observed by near-Earth spacecrafts. On 7 September and 10 September 2017, a strong enhancement in the proton intensities was observed by ACE and WIND at L1 and Van Allen Probes, GOES-15 and POES-19 in the Earth’s inner magnetosphere. Below geosynchronous orbit, Van Allen Probes and POES-19 shows that no significant proton flux was observed with energies 25 MeV on September 4, while the fluxes peaked 3 to 7-times during September 7 and by 25 times during the third proton flux event on 10 September, 2017. Van Allen Probe-A observation shows that the closest distance that solar proton fluxes could approach the Earth is 4.4 for 102.6 MeV energies on September 2017, while lower energy protons i.e. 25 MeV are observed deep up to 3.4 on September 2017. POES-19 observations show that there is no particular MLT dependence of the solar proton flux and is symmetric everywhere at high and low latitudes. The measurements from multiple spacecrafts located in the different regions of the Earth’s magnetosphere show that the increased level of solar proton flux population persisted for 2 days. Thus we quantify the temporal flux variability in terms of -value, energy and MLT.