Trapped Proton Environment in Medium-Earth Orbit (2000-2010)

TL;DR

This paper presents a new empirical proton radiation-belt model for Medium-Earth Orbit during 2000-2010, utilizing GPS data and measurements from the Polar mission, providing improved flux estimates and uncertainty analysis.

Contribution

Developed a novel empirical proton belt model based on Polar data, scaled with GPS measurements, offering more accurate flux estimates and statistical information over the standard AP8 model.

Findings

The new model shows significant differences from AP8, indicating underestimation of belt variations by previous models.

Flux uncertainties are quantified, with error factors less than 3 from the model and around 5 from measurements.

Derived daily proton fluxes along GPS orbit for the 2000-2010 period, illustrating the trapped proton environment.

Abstract

This report describes the method used to derive fluxes of the trapped proton belt along the GPS orbit (i.e., a Medium-Earth Orbit) during 2000-2010, a period almost covering a solar cycle. This method utilizes a newly developed empirical proton radiation-belt model, with the model output scaled by GPS in-situ measurements, to generate proton fluxes that cover a wide range of energies (50keV- 6MeV) and keep temporal features as well. The new proton radiation-belt model is developed based upon CEPPAD proton measurements from the Polar mission (1996 - 2007). Comparing to the de-facto standard empirical model of AP8, this model is not only based upon a new data set representative of the proton belt during the same period covered by GPS, but can also provide statistical information of flux values such as worst cases and occurrence percentiles instead of solely the mean values. The comparison shows quite different results from the two models and suggests that the commonly accepted error factor of 2 on the AP8 flux output over-simplifies and thus underestimates variations of the proton belt. Output fluxes from this new model along the GPS orbit are further scaled by the ns41 insitu data so as to reflect the dynamic nature of protons in the outer radiation belt at geomagnetically active times. Derived daily proton fluxes along the GPS ns41 orbit, whose data files are delivered along with this report, are depicted to illustrate the trapped proton environment in the Medium-Earth Orbit. Uncertainties on those daily proton fluxes from two sources are evaluated: One is from the new proton-belt model that has error factors < ~3; the other is from the in-situ measurements and the error factors could be ~ 5.