A Generalized Method for Calculating Atmospheric Ionization by Energetic Electron Precipitation
Monday, 7 December 2020: 17:51
Virtual
Wei Xu1, Robert Andrew Marshall1, Hilde Nesse Tyssøy2 and Xiaohua Fang3, (1)University of Colorado at Boulder, Aerospace Engineering Sciences, Boulder, CO, United States, (2)University of Bergen, Birkeland Centre for Space Science (BCSS), Department of Physics and Technology, Bergen, Norway, (3)University of Colorado at Boulder, Laboratory for Atmospheric and Space Physics, Boulder, CO, United States
Abstract:
Energetic electron precipitation (EEP) causes significant disturbances to the entire magnetosphere-ionosphere-atmosphere system, including the dynamics of the radiation belts, and the thermal, electrical, and chemical properties of the Earth’s atmosphere. Accurate specification of ionization production by EEP is critical for atmospheric chemistry models to assess the resultant atmospheric effects. Recent model-observation comparison studies have increasingly highlighted the importance of considering precipitation fluxes in the full range of electron energy and pitch angle: Nesse Tyssøy et al. [JGR, 121, 5693, 2016] combined measurements from the 0˚and 90˚telescopes of the Medium Energy Proton and Electron Detector (MEPED) onboard the Polar Orbiting Environmental Satellites (POES), and revealed that the comparison with observational data achieved good agreements only after taking the full pitch angle distribution into account. Pettit et al. [JGR, 124, 8138, 2019] also found that including more information of precipitation pitch angle greatly improves the agreements with measurements of reactive odd nitrogen at middle latitudes. However, previous parameterization methods were mostly proposed for isotropically-precipitation electrons with energies up to 1 MeV and the pitch angle dependence has not yet been parameterized.
In this study, we first characterize and tabulate the atmospheric ionization response to monoenergetic electrons with different pitch angles and energies between ~3 keV and ~33 MeV. A generalized method that fully accounts for the dependence of ionization production on background atmospheric conditions, electron energy, and pitch angle has been developed. Moreover, we validate this method using 100 random atmospheric profiles and precipitation fluxes with monoenergetic and exponential energy distributions, and isotropic and sine pitch angle distributions. In a suite of 6,100 validation tests, the error in peak ionization altitude is found to be within 1 km in 91% of all the tests with a mean error of 2.7% in peak ionization rate, and 1.9% in total ionization. This method therefore provides a reliable means to convert space-measured precipitation energy and pitch angle distributions into ionization inputs for atmospheric chemistry models.
