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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/angeo-2020-36
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2020-36
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  02 Jun 2020

02 Jun 2020

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A revised version of this preprint was accepted for the journal ANGEO and is expected to appear here in due course.

Odd hydrogen response thresholds for indication of solar proton and electron impact in the mesosphere and stratosphere

Tuomas Häkkilä1, Pekka T. Verronen1,2, Luis Millán3, Monika E. Szela̧g1, Niilo Kalakoski1, and Antti Kero2 Tuomas Häkkilä et al.
  • 1Space and Earth Observation Centre, Finnish Meteorological Institute, Helsinki, Finland
  • 2Sodankylä Geophysical Observatory, University of Oulu, Sodankylä, Finland
  • 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

Abstract. Understanding the atmospheric forcing from energetic particle precipitation (EPP) is important for climate simulations on decadal time scales. However, presently there are large uncertainties in energy-flux measurements of electron precipitation. One approach to narrow these uncertainties is by analyses of EPP direct atmospheric impacts and their relation to measured EPP fluxes. Here we use odd hydrogen observations from the Microwave Limb Sounder and Whole Atmosphere Community Climate Model simulations, together with EPP fluxes from the GOES and POES satellites, to determine the response thresholds to solar proton events (SPEs) and radiation belt electron (RBE) precipitation. We consider a range of altitudes in the middle atmosphere, and all magnetic latitudes from pole to pole. We find that the lower flux limits for day-to-day EPP impact detection using OH and HO2 are of the order of 102 protons/cm2/s/sr (E > 10 MeV) and 104 electrons/cm2/s/sr (E = 100–300 keV). Based on the simulations, nighttime OH and HO2 are good EPP indicators in the polar regions, and provide best coverage in altitude and latitude. Due to larger background concentrations, daytime detection requires larger EPP fluxes and is possible in the mesosphere only. SPE detection is easier than RBE detection because a wider range of polar latitudes is affected. We also find that MLS OH observations indicate a clear nighttime response to SPE and RBE in the mesosphere, similar to the simulations, while HO2 data are overall too noisy for confident EPP detection.

Tuomas Häkkilä et al.

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Tuomas Häkkilä et al.

Tuomas Häkkilä et al.

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Latest update: 24 Nov 2020
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Short summary
The atmospheric impacts of energetic particle precipitation (EPP) can be useful in understanding the uncertainties of measuring the precipitation. Hence information on how strong of an EPP flux has observable atmospheric impacts is needed. In this study we find such threshold flux values using odd hydrogen concentrations from both satellite observations and model simulations. We consider effects of solar proton events and radiation belt electron precipitation in the middle atmosphere.
The atmospheric impacts of energetic particle precipitation (EPP) can be useful in understanding...
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