Subauroral contamination in POES/Metop TED channels

Abstract

Particle measurements from the Polar Operational Environmental Satellites (POES) and the Meteorological Operational (Metop) satellite program, are widely used for various scientific applications. While most studies focus on the Medium Energy Proton and Electron Detector (MEPED), the low-energy (eV and keV) counterpart, the Total Energy Detector (TED), has received comparatively less attention. However, the recent rise in the altitudes considered in ionization and climate models has increased interest in low-energy particle measurements as inputs for atmospheric ionization models. This study analyzes TED particle data (together with selected MEPED channels) from 2001 to 2025 and shows that the TED 0° proton channels, in particular, are contaminated by energetic electrons at L < 6, with weaker contamination observed in other TED channels. In some cases, the contaminated fluxes exceed typical auroral flux levels. The affected regions were cross-validated using auroral UV emissions and occurrences of GNSS derived S4 index to rule out the possibility that the observed fluxes correspond to real particle precipitation. As correction approach, we provide a simple Kp- and channel-dependent latitude boundary that may serve as preliminary cut-off criterion for the contaminated regions. In a more advanced step, we identified the contamination characteristics of each particle channel on each satellite. The outcome is a list of problematic channels that should be neglected and a correction method based on background counts for the other channels. The corrected fluxes are in good agreement with UV emissions and the method is available in the additional material.