New Homogeneous Composite of Energetic Electron Fluxes From POES Satellites: 1. Correction for Background Noise and Orbital Drift

摘要

One of the most popular long-term data sets of energetic particles used in, for example, long-term radiation belt studies and in atmospheric/climate studies is perhaps the National Oceanic and Atmospheric Administration/Polar Orbiting Environmental Satellites (POES) data set, which extends nearly continuously from 1979 to present. The energetic particle measurements by the Medium Energy Proton and Electron Detector instrument onboard the POES satellites have had many instrumental problems, which have made quantitative estimates of energetic particle fluxes somewhat difficult. However, in the recent years, these instrumental deficiencies have been studied and corrected. Here we aim to construct a new long-term composite record of energetic electrons based on the Medium Energy Proton and Electron Detector data. In this study we point out that there are also other remaining factors, not related to instrument construction, which still severely impact the overall homogeneity of the 39-year POES data set. We concentrate here on studying and correcting two issues: (1) temporally varying background noise related to cosmic rays and (2) drift in the orientation of satellite orbital planes, which changes the sampling location of the satellites over time. In particular, we show that the drift of satellite orbital planes leads to rather large changes in the electron fluxes over time, which could be misinterpreted as true temporal changes without the corrections. These changes can be rather large, a factor of 3 or more in the poleward edge of the precipitation zone, and are likely to have a large impact, for example, on atmospheric ionization estimates based on POES data. Plain Language Summary One of the longest satellite records of energetic electrons has been measured by the Polar Orbiting Environmental Satellites (POES) since 1979. These data are actively being used to study, for example, radiation belts and atmospheric and climate effects of energetic particle precipitation. Here we point out two problems jeopardizing the homogeneity of the long-term POES record of energetic electrons: (1) varying level of background noise related to high-energy cosmic rays that contaminate the measurements and (2) slow change of the orientation of satellite orbital planes, which changes the location where electrons are being measured. In particular, we show that the orbital change can lead to large long-term drifts in the measurements, which could be misinterpreted as being true temporal changes without the corrections presented here. These changes can be rather large, a factor of 3 or more, and are likely to have a large impact, for example, on atmospheric ionization estimates based on POES data, which are used to study climate effects of energetic electron precipitation.