Hilde Nesse Tyssøy

In‐flight calibration of NOAA POES proton detectors—Derivation of the MEPED correction factors

The MEPED instruments on board the NOAA POES andMetOp satellites have been continuously measuring energetic particles in the magnetosphere since 1978. However, degradation of the proton detectors over time leads to an increase in the energy thresholds of the instrument and imposes great challenges to studies of long-term variability in the near-Earth space environment as well as a general quantification of the proton fluxes. By comparing monthly mean accumulated integral flux from a new and an old satellite at the same magnetic local time (MLT) and time period, we estimate the change in energy thresholds. The first 12 monthly energy spectra of the new satellite are used as a reference, and the derived monthly correction factors over a year for an old satellite show a small spread, indicating a robust calibration procedure. The method enables us to determine for the first time the correction factors also for the highest-energy channels of the proton detector. In addition, we make use of the newest satellite in orbit (MetOp-01) to find correction factors for 2013 for the NOAA 17 and MetOp-02 satellites. Without taking into account the level of degradation, the proton data from one satellite cannot be used quantitatively for more than 2 to 3 years after launch. As the electron detectors are vulnerable to contamination from energetic protons, the corrected proton measurements will be of value for electron flux measurements too. Thus, the correction factors ensure the correctness of both the proton and electron measurements.

Space Weather impact on the degradation of NOAA POES MEPED proton detectors

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.

The impact of energetic electron precipitation on mesospheric hydroxyl during a year of solar minimum

©2016. The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Direct and indirect electron precipitation effect on nitric oxide in the polar middle atmosphere, using a full-range energy spectrum

In April 2010, a coronal mass ejection and a corotating interaction region on the Sun resulted in an energetic electron precipitation event in the Earths atmosphere. We investigate direct and indirect nitric oxide (NO) response to the electron precipitation. By combining electron fluxes from the Total Energy Detector (TED) and the Medium Energy Proton and Electron Detector (MEPED) on the National Oceanic and Atmospheric Administrations (NOAAs) Polar Orbiting Environmental Satellites (POES), we obtain a continuous energy spectrum covering 1-750 keV. This corresponds to electrons depositing their energy at atmospheric altitudes 60-120 km. Based on the electron energy deposition, taking into account loss due to photolysis, the accumulated NO number density is estimated. When compared to NO measured at these altitudes by the Solar Occultation for Ice Experiment (SOFIE) instrument on board the Aeronomy of Ice in the Mesosphere (AIM) satellite, the NO direct effect was detected down to 55 km. The main variability at these altitudes is however dominated by the indirect effect, which is downward transported NO. We estimate the source of this descending NO to be in the upper mesosphere at ∼75-90 km.

Energetic electron precipitation in weak to moderate corotating interaction region-driven storms

High-energy electron precipitation from the radiation belts can penetrate deep into the mesosphere and increase the production rate of NOx and HOx , which in turn will reduce ozone in catalytic processes. The mechanisms for acceleration and loss of electrons in the radiation belts are not fully understood, and most of the measurements of the precipitating flux into the atmosphere have been insufficient for estimating the loss cone flux. In the present study the electron flux measured by the NOAA POES Medium Energy Proton and Electron Detectors 0∘ and 90∘ detectors is combined together with theory of pitch angle diffusion by wave-particle interaction to quantify the electron flux lost below 120 km altitude. Using this method, 41 weak and moderate geomagnetic storms caused by corotating interaction regions during 2006–2010 are studied. The dependence of the energetic electron precipitation fluxes upon solar wind parameters and geomagnetic indices is investigated. Nine storms give increased precipitation of > ∼ 750 keV electrons. Nineteen storms increase the precipitation of > ∼300 keV electrons, but not the >∼750 keV population. Thirteen storms either do not change or deplete the fluxes at those energies. Storms that have an increase in the flux of electrons with energy >∼ 300 keV are characterized by an elevated solar wind velocity for a longer period compared to the storms that do not. Storms with increased precipitation of >∼750 keV flux are distinguished by higher-energy input from the solar wind quantified by the ε parameter and corresponding higher geomagnetic activity.

Nitric Oxide Response to the April 2010 Electron Precipitation Event: Using WACCM and WACCM‐D With and Without Medium‐Energy Electrons

Energetic electrons from the magnetosphere deposit their energy in the atmosphere and lead to production of nitric oxide (NO) in the mesosphere and lower thermosphere (MLT). We study the atmospheric NO response to a geomagnetic storm in April 2010 with WACCM (Whole Atmosphere Community Climate Model). Modeled NO is compared to observations by SOFIE/AIM (Solar Occultation For Ice Experiment / Aeronomy of Ice in the Mesosphere) at 72‐82° S latitudes. We investigate the modeled NOs sensitivity to changes in energy and chemistry. The electron energy model input is either a parameterization of auroral electrons or a full range energy spectrum (1‐750 keV) from NOAA/POES (National Oceanic and Atmospheric Administration / Polar Orbiting Environmental Satellites) and EUMETSAT/MetOp (European Organisation for the Exploitation of Meteorological Satellites / Meteorological Operational satellites). To study the importance of ion chemistry for the production of NO, WACCM‐D, which has more complex ion chemistry, is used. Both standard WACCM and WACCM‐D underestimate the storm time NO increase in the main production region (90‐110 km), using both electron energy inputs. At and below 80 km, including medium energy electrons (>30 keV) is important both for NO directly produced at this altitude region and for NO transported from other regions (indirect effect). By using WACCM‐D the direct NO production is improved, while the indirect effects on NO suffer from the downward propagating deficiency above. In conclusion, both a full range energy spectrum and ion chemistry is needed throughout the MLT region to increase the direct and indirect contribution from electrons on NO.