Correcting the NOAA/MEPED energetic electron fluxes for detector efficiency and proton contamination

Abstract

The Medium Energy Proton and Electron Detector (MEPED) instruments onboard the NOAA/POES satellites have provided a valuable long‐term database of low‐altitude energetic particle observations spanning from 1978 to present. Here we study the instrumental problems of the NOAA/MEPED electron detectors and present methods to correct them. It is well known that the MEPED electron detectors are contaminated by protons of certain energy range. Using the recently corrected MEPED proton fluxes, we are now able to reliably remove this contamination. Using a simple simulation model to estimate the response of the MEPED electron detectors to incoming electrons and protons, we show that efficiencies of (Space Environment Monitors) SEM‐1 and SEM‐2 versions of the detectors have large differences due to different detector designs. This leads to a systematic difference between the SEM‐1 and SEM‐2 measurements and causes a significant long‐term inhomogeneity in measured MEPED electron fluxes. Using the estimated efficiencies, we remove the proton contamination and correct the electron measurements for nonideal detector efficiency. We discuss the entire 34 year time series of MEPED measurements and show that, on an average, the correction affects different energy channels and SEM‐1 and SEM‐2 instruments differently. Accordingly, the uncorrected electron fluxes and electron spectra are severely distorted by nonideal detector efficiency and proton contamination, and their long‐term evolution is misrepresented without the correction. The present correction of the MEPED electron fluxes over the whole interval of NOAA/POES measurements covering several solar cycles is important for long‐term studies of, e.g., magnetospheric dynamics, solar activity, ionospheric research, and atmospheric effects of energetic electrons.