Impacts of Energetic Electron Precipitation on the Middle Atmosphere

Peck, Ethan D.

Graduate Thesis Or Dissertation

Impacts of Energetic Electron Precipitation on the Middle Atmosphere Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/jq085k039

Abstract

Energetic particle precipitation (EPP) can have profound impacts on the middle atmosphere. NO_x produced by EPP in the thermosphere and mesosphere can descend into the stratosphere during polar night; after being sequestered by the polar vortex until spring, NO_x can destroy stratospheric O₃ (>25 km) in a catalytic cycle. Changes to O₃ can change local temperatures and in turn zonal wind through thermal wind balance.

This work seeks to understand the impacts of medium energy electrons (MEE) (25 keV – 2 MeV), a subset of EPP, on the middle atmosphere. Data from the Medium Energy Proton/Electron Detector (MEPED) is assimilated into the Whole Atmosphere Community Climate Model (WACCM). This is accomplished in three steps: (1) examine the response of WACCM to solar cycle; (2) improve and prepare MEPED data for use in WACCM; and (3) simulate MEE precipitation in WACCM.

WACCM is able to simulate solar cycle impacts in general agreement with observations and reanalysis. Auroral EPP (<30 >keV) produced NO_x is found to destroy >10% more O₃ in solar maximum simulations than solar minimum simulations. Temperature and zonal wind results match reanalysis in the northern hemisphere (NH), but not in the southern hemisphere (SH). Disagreements are likely caused by the Antarctic "cold-pole problem."

This work removes proton contamination from MEPED electron channels and outputs spectral count flux for protons and electrons by using an inversion technique with a combination of best fit spectra. Results are in agreement with the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) Instrument for Detecting Particles (IDP).

MEE spectral flux is converted into precipitating flux and assimilated into specified dynamics WACCM (SD-WACCM). Production by MEE is large (>100 ppbv at 80 km). MEE NO_x production is too high below 80 km, and too low above 80 km. SD-WACCM is also found to have too strong winter polar descent. MEE precipitation is believed to be capable of producing NOₓ to match observations, but production at the wrong altitudes and incorrect descent prevent further analysis into impacts on the middle atmosphere.

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