Energetic particle precipitation into the middle atmosphere - optimization and applications of the NOAA POES MEPED data
Not peer reviewed
MetadataShow full item record
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.