Recalibration of the MEPED Proton Detectors Onboard NOAA POES Satellites

In this thesis we have calibrated energetic proton data from the solid state detectors of the MEPED instrument onboard the satellites NOAA 15, 16, 17, 18, and MetOp 02. All these satellites are part of the NOAA/POES program, they fly in polar orbits in 800-850 km altitude, and they carry a suite of almost identical instrumentation. For over 30 years the NOAA/POES satellites have collected valuable information about the particle environment in the Earth's magnetosphere and ionosphere. However, with time these solid state detectors suffer from radiation damage due to energetic particles, which leads to increasing energy thresholds and increasing underestimation of particle fluxes. Data from different satellites must therefore be inter-calibrated in order to be used for quantitative studies. In this thesis we have developed two statistical methods for calibration of the energetic proton data from MEPED instrument onboard the NOAA satellites. The first method is used for calibration when two spacecraft are in the same magnetic local time sector. This method is applied to data from NOAA 16 in 2005, NOAA 17 in 2007, and NOAA 18 in 2009, when these satellites were fortunate to share the orbit with a newly launched satellite. We compare energy spectra based on daily averaged fluxes and estimate the increased energy thresholds of the MEPED instrument in these years. The second method is used to calibrate satellite data at different magnetic local times. Average maps of the flux of energetic protons as a function of magnetic local time and invariant latitude were constructed for different levels of magnetic activity given by the Kp index. By determining the local time dependence of the fluxes in the isotropic zone, these maps were used to calibrate old satellites that were separated in magnetic local time relative to new satellites. This method allows for a better estimation of the temporal evolution of the energy thresholds of the MEPED instruments.Master i FysikkMAMN-PHYSPHYS39

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

The MEPED instruments on board the NOAA POES and MetOp 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.publishedVersio

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

Under embargo until: 2018-02-03In April 2010, a coronal mass ejection and a corotating interaction region on the Sun resulted in an energetic electron precipitation event in the Earth’s atmosphere. We investigate direct and indirect nitric oxide (NO) response to the electron precipitation. By combining electron fluxes from the Total Energy Detector and the Medium Energy Proton and Electron Detector on the National Oceanic and Atmospheric Administration’s Polar-orbiting Operational Environmental Satellites, 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 instrument on board the Aeronomy of Ice in the Mesosphere 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.publishedVersio

Recalibration of the MEPED Proton Detectors Onboard NOAA POES Satellites

In this thesis we have calibrated energetic proton data from the solid state detectors of the MEPED instrument onboard the satellites NOAA 15, 16, 17, 18, and MetOp 02. All these satellites are part of the NOAA/POES program, they fly in polar orbits in 800-850 km altitude, and they carry a suite of almost identical instrumentation. For over 30 years the NOAA/POES satellites have collected valuable information about the particle environment in the Earth's magnetosphere and ionosphere. However, with time these solid state detectors suffer from radiation damage due to energetic particles, which leads to increasing energy thresholds and increasing underestimation of particle fluxes. Data from different satellites must therefore be inter-calibrated in order to be used for quantitative studies. In this thesis we have developed two statistical methods for calibration of the energetic proton data from MEPED instrument onboard the NOAA satellites. The first method is used for calibration when two spacecraft are in the same magnetic local time sector. This method is applied to data from NOAA 16 in 2005, NOAA 17 in 2007, and NOAA 18 in 2009, when these satellites were fortunate to share the orbit with a newly launched satellite. We compare energy spectra based on daily averaged fluxes and estimate the increased energy thresholds of the MEPED instrument in these years. The second method is used to calibrate satellite data at different magnetic local times. Average maps of the flux of energetic protons as a function of magnetic local time and invariant latitude were constructed for different levels of magnetic activity given by the Kp index. By determining the local time dependence of the fluxes in the isotropic zone, these maps were used to calibrate old satellites that were separated in magnetic local time relative to new satellites. This method allows for a better estimation of the temporal evolution of the energy thresholds of the MEPED instruments

Energetic particle precipitation into the middle atmosphere - optimization and applications of the NOAA POES MEPED data

This thesis has been a part of the research in the Q3 group of the Birkeland Centre for Space Science, which focus on the larger question "What are the effects of particle precipitation on the atmosphere?". An important step towards achieving an answer has been to optimize the NOAA POES MEPED data, which contain measurements of protons and electrons in the medium to high energy range. The particles measured by MEPED can penetrate deep into the atmosphere and create ionization, which ultimately can affect chemistry, temperature and dynamics. There have, unfortunately, been some challenges with the MEPED detectors. The proton detectors of the MEPED instrument are known to degrade with time. In addition, the proton measurements can be contaminated by relativistic electrons. Adding to this, the electron measurements have also been reported to suffer from low-energy proton contamination. Finally, the detectors only cover a limited part of the particle pitch angle distribution being lost to the atmosphere. In paper I (Sandanger et al., 2015) we present a robust method for correcting the MEPED proton detector degradation. We show that when the correction is applied to the degraded SEM-2 detectors, the long time flux series measured by the different satellites agree extremely well. Without correction, the data from a detector could not be used after only a few years in operation. For the very first time, we present correction factors for the MEPED proton channels with highest energy. In paper II (Ødegaard et al., 2016a), we use the correction factors for the MEPED proton detectors derived in paper I and show that they exhibit a varying trend in degradation rate throughout the solar cycle. The degradation rate is found to be strongest in the declining phase of the solar cycle. We exploit this trait and present a model which can be used to estimate the correction factor of any of the SEM-2 MEPED detectors. This allowed for the calculation of yearly correction factors throughout all SEM-2 operational periods. It may also be used to correct the SEM-1 detectors, enabling long term studies of energetic particle precipitation. In paper III (Nesse Tyssøy et al., 2016), we tackle challenges related to the MEPED electron detector. We take advantage of the MEPED proton detectors’ response to relativistic electrons and provide an additional measurement to the electron spectrum. We also correct for discrepancies between the reported geometric factors of the MEPED instrument and the modelled geometric factors. An effect of this is that the threshold of the lowest energy channel is raised from > 30 keV to > 50 keV. However, the most important result in this paper is that we combine measurements from the two directional telescopes of the MEPED, and use pitch angle distributions from theory of wave-particle interactions to present complete bounce loss cone fluxes for > 50 keV, > 100 keV, > 300 keV and > 1000 keV electrons. These energies cover the range of electron precipitation which will deposit energy in the middle atmosphere. The bounce loss cone fluxes are substantiated by estimating the OH produced during a weak storm, and comparing with OH observations from the Aura satellite. In paper IV (Ødegaard et al., 2016b), we use the bounce loss cone fluxes to study precipitation during storms driven by corotating interaction regions. We find that a group of storms that give increased precipitation of > 1 MeV electrons are associated with high solar wind speeds and a higher energy input to the magnetosphere from the solar wind, as estimated by the Akasofu Epsilon parameter. These findings might offer an opportunity to the atmospheric modelling community to improve their estimates of energetic electron precipitation

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

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

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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. 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 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 National Oceanic and Atmospheric Administration/Polar Orbiting Environmental Satellites and 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 mesosphere and lower thermosphere region to increase the direct and indirect contribution from electrons on NO