Long-Term Impacts on the Middle and Upper Atmosphere from Energetic Electron Precipitation

Energetic particle precipitation (EPP) can have large impacts on the chemistry of the middle and upper atmosphere. The three types of precipitating particles that are of importance in this region are solar protons from the Sun, auroral electrons from the plasma sheet, and higher energy electrons from the magnetosphere ring current and radiation belts. Solar protons can have large impacts on reactive odd nitrogen (NOx), odd hydrogen (HOx) and ozone in the mesosphere and stratosphere, however they occur relatively infrequently, maximizing near solar cycle maximum. Auroral electrons, which typically have energies < 30 keV, precipitate continuously but deposit their energy in the thermosphere; their effects on the middle atmosphere are thus indirect. Electrons with energies > 30 keV, on the other hand, precipitate regularly to altitudes ranging from the lower thermosphere through the upper stratosphere. The long-term contribution to the chemistry of the middle atmosphere from these higher energy electrons could therefore exceed that of other forms of EPP. This work investigates both short-term and long-term impacts on the stratosphere, mesosphere and lower thermosphere from EPP, with a focus on the higher energy precipitating electrons. Simulations were performed using the Whole Atmosphere Community Climate Model (WACCM6) that includes solar protons, auroral electrons and a new data set for higher energy precipitating electrons that utilizes the Medium Energy Proton and Electron Detector (MEPED) instruments named the MEPED Precipitating Electron (MPE) data set. The forced simulations are compared to a baseline WACCM6 simulation that excluded the higher energy electrons of > 30 keV. The simulations included the time frame from 1 January 2001 through January 1 2019, which captures nearly two full solar cycles.