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The Medium Energy Proton and Electron Detector (MEPED) on board the National Oceanic and Atmospheric Administration Polar Orbiting Environmental Satellites (NOAA POES) is known to degrade with time. In recent years a lot of effort has been put into calibrating the degraded proton detectors. We make use of previous work and show that the degradation of the detectors can be attributed to the radiation dose of each individual instrument. However, the effectiveness of the radiation in degrading the detector is modulated when it is weighted by the mean ap index, increasing the degradation rate in periods with high geomagnetic activity, and decreasing it through periods of low activity. When taking ap and the radiation dose into account, we find that the degradation rate is independent of spacecraft and detector pointing direction. We have developed a model to estimate the correction factor for all the MEPED detectors as a function of accumulated corrected flux and the ap index. We apply the routine to NOAA POES spacecraft starting with NOAA-15, including the European satellites MetOp-02 and MetOp-01, and estimate correction factors.

Energetic particle precipitation (EPP) increases the production of odd hydrogen (HOX) species in the mesosphere, which catalytically destroy ozone (O3) in sunlight. Hence, the EPP‐HOX impact on the tertiary O3 maximum (TOM) depends on a complex geometry of a geographic‐oriented TOM, geomagnetic‐oriented auroral zone, producing short‐lived HOX species, and a destruction process depending on the solar zenith angle (SZA). Particle observations from the Medium Energy Proton and Electron Detectors telescopes aboard the Polar Orbiting Environmental Satellites, and hydroxyl (OH) and O3 mixing ratios from Aura microwave limb sounder (MLS) are used to investigate the potential limitations of using the MLS observations to study EPP‐OH impact on the TOM in the Northern Hemisphere. Our results show limited overlap between the auroral zone and the TOM at twilight conditions. A composite analysis indicates O3 mixing ratio decrease over the auroral zone lagged by ∼1 day compared to the maximum energetic electron precipitation (EEP)‐OH impact. Hence, MLS is predominantly observing a lagged and lower estimate of the response of O3 to EEP‐OH at SZA > 95°. The EEP impact region within the TOM is smaller than the overlap region, strongly modulated by the background atmospheric dynamics. The results, although limited by the satellites viewing conditions, imply that the importance of EEP upon O3 mixing ratio is strongly influenced by the background atmosphere, both in terms of chemistry and dynamics. Multisatellite observations at different solar local times are required to separate the direct from the lagged EEP‐OH impact on O3. Key Points: MLS provides a unique opportunity to study the direct impact of energetic particle precipitation on mesospheric hydroxyl (OH) and ozone (O3)There is limited overlap between the auroral zone and the tertiary O3 maximum at twilight conditionsThe importance of energetic electron precipitation on the tertiary O3 maximum is strongly governed by the background atmosphere [ABSTRACT FROM AUTHOR]

Abstract: Using a new analysis technique, we estimate the precipitating particle fluxes measured by the Medium Energy Proton and Electron Detector on the National Oceanic and Atmospheric Administration Polar Orbiting Environmental Satellites. These fluxes are used to quantify the direct impact of energetic particle precipitation (EPP) on mesospheric hydroxyl (OH) measured from the Aura satellite during 2005–2009 in the Northern Hemisphere, covering the declining and minimum phase of solar cycle 23. Using multiple linear regression of nighttime OH volume mixing ratio with temperature, geopotential height, water vapor (H2O) volume mixing ratio, Lyman‐alpha (Ly‐α) radiation, and particle energy deposition, we account for the background variability and hence the EPP impact independent of season and other short‐term variability. We investigate the relative importance of solar proton events, energetic electron precipitation and the background to OH variability. The background dominates over EPP above 70‐km altitude. Below 70 km, EPP dominates. The maximum EPP contribution is 44% and 34% in the geographic and corrected geomagnetic (CGM) settings respectively at 67 km. Protons dominate over electrons at mesospheric altitudes with maximum contributions of 43% and 32% at 67 km in the geographic and CGM settings, respectively. In a CGM setting, the electrons contribution is comparable to that of protons above 70 km, with a maximum contribution of 11% at 75 km. Since the period investigated is during relatively low solar activity, these results represent a lower estimate of the general EPP contribution to OH variability. [ABSTRACT FROM AUTHOR]