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GOES SGPS Alpha Particles
GOES Solar and Galactic Proton Sensors (SGPS) alpha particle measurements.
The GOES Solar and Galactic Proton Sensor Alpha particle measurements provide real time monitoring of the radiation environment at Earth and provide inputs for models serving the aviation, satellite, and human space exploration industries.
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Alpha particles (helium-4 nuclei) are significant contributors to dose rates during solar energetic particle (SEP) events. Real-time measurements of alpha particle fluxes are required for inputs to models serving the aviation, satellite, and human space exploration industries. The GOES 16-19 alpha particle fluxes are measured by the two Solar and Galactic Proton Sensors (SGPS) on each satellite, the same instrument that measures the solar proton fluxes used by SWPC for solar radiation storm alerts. One SGPS looks eastward, and one looks westward in the orbit. The ion fluxes that are incident on the westward-looking telescopes are least attenuated by the shielding effects of the geomagnetic field. The capability of the spacecraft to perform a yaw flip, which results in a switch of the eastward- and westward-looking directions, drives the requirement for two SGPS units on each spacecraft. The proton fluxes from the westward-looking SGPS are used for SWPC’s solar radiation storm alerts.
From each SGPS, eleven alpha particle energy channels are processed (Table 1). The JSON files contain 5-minute averages of the SGPS alpha particle fluxes at all eleven energies from the SGPS unit that looks westward. The files also contain the lower and upper channel energies. An ‘effective’ center energy can be approximated as the geometric mean of the lower and upper energies, though, strictly speaking, this is only correct for a power law exponent of -2. Background levels from galactic cosmic rays have not been removed from these fluxes.
Note: The energy units in the SGPS files are keV, not MeV, because of the way the GOES SGPS requirements were written.
- To convert channel energies from keV to MeV, divide by 1000.
- To convert alpha particle fluxes from α/cm²-s-sr-keV to α/cm²-s-sr-MeV, multiply by 1000.
To convert alpha particle fluxes from α/cm²-s-sr-MeV to α/cm²-s-sr-(MeV/nucleon), multiply by 4.
| Channel Designation | Lower Energy (MeV) | Upper Energy (MeV) |
|---|---|---|
| A1 | 3.79 | 6.78 |
| A2A | 7.98 | 8.58 |
| A2B | 9.18 | 12.8 |
| A3 | 15.2 | 27.1 |
| A4 | 30.1 | 49.2 |
| A5 | 55.8 | 99.5 |
| A6 | 104.0 | 158.0 |
| A7 | 164.0 | 286.0 |
| A9 | 318.0 | 380.0 |
| A10 | 394.0 | 485.0 |
| A11 | 573.0 | 894.0 |