Polar Ozone Response to Energetic Particle Precipitation Over Decadal Time Scales: The Role of Medium‐Energy Electrons

Abstract

One of the key challenges in polar middle atmosphere research is to quantify the total forcing by energetic particle precipitation (EPP) and assess the related response over solar cycle time scales. This is especially true for electrons having energies between about 30 keV and 1 MeV, so‐called medium‐energy electrons (MEE), where there has been a persistent lack of adequate description of MEE ionization in chemistry‐climate simulations. Here we use the Whole Atmosphere Community Climate Model (WACCM) and include EPP forcing by solar proton events, auroral electron precipitation, and a recently developed model of MEE precipitation. We contrast our results from three ensemble simulations (147 years) in total with those from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) in order to investigate the importance of a more complete description of EPP to the middle atmospheric ozone, odd hydrogen, and odd nitrogen over decadal time scales. Our results indicate average EPP‐induced polar ozone variability of 12–24% in the mesosphere, and 5–7% in the middle and upper stratosphere. This variability is in agreement with previously published observations. Analysis of the simulation results indicate the importance of inclusion of MEE in the total EPP forcing: In addition to the major impact on the mesosphere, MEE enhances the stratospheric ozone response by a factor of 2. In the Northern Hemisphere, where wintertime dynamical variability is larger than in the Southern Hemisphere, longer simulations are needed in order to reach more robust conclusions.

Observations and Modeling of Increased Nitric Oxide in the Antarctic Polar Middle Atmosphere Associated With Geomagnetic Storm‐Driven Energetic Electron Precipitation

“…The differences between the two WACCM‐SIC runs are very similar to those reported for WACCM simulations over decadal timescales (Andersson et al, ) in which 30–1,000 keV EEP was introduced using an Ap index‐driven model (van de Kamp et al, ), rather than the electron observation‐based estimates of MEE ionization used in this study. For the polar SH (geographic latitude range 60°–90°S) the Andersson et al () model calculations show the largest relative increases in NO x during the summer, exceeding 200% at altitudes ~75–90 km. During mid‐winter the Ap index‐driven MEE ionization increased average mesospheric NO x by over 20%.…”

“…The differences between the two WACCM-SIC runs are very similar to those reported for WACCM simulations over decadal timescales (Andersson et al, 2018) in which 30-1,000 keV EEP was introduced using an Ap index-driven model (van de Kamp et al, 2016), rather than the electron observation-based estimates of MEE ionization used in this study. The SOFIE observations and WACCM-SIC simulation results are compared in Figure 9, which shows NO number density at 10 km intervals from 60 to 110 km after applying a 31-day moving average to each of the three data sets.…”

Atmospheric Effects of >30‐keV Energetic Electron Precipitation in the Southern Hemisphere Winter During 2003

“…Atmospheric effects of solar D protons and auroral electrons (energy < 30 keV) have been studied extensively over the last few decades (Crutzen, 1979;Funke et al, 2011;Jackman et al, 1995;Jackman & McPeters, 2004;Jackman et al, 2008;Jackman et al, 2009;López-Puertas et al, 2005;Orsolini et al, 2005;Roble & Rees, 1977). Particularly in the past several years, more attention has been paid to medium energy electron (MEE,~30-1,000 keV) and high-energy electron (HEE, >1 MeV) precipitation influences on the atmosphere (Andersson et al, 2018;Clilverd et al, 2013;Newnham et al, 2018;Seppälä et al, 2018;Verronen et al, 2015). Evaluating two different energetic electron precipitation (EEP) data sets for inclusion in global climate models, both of which include MEE precipitation inferred from the Medium Energy Proton and Electron Detector (MEPED) instruments, is the focus of this paper.…”

“…Eyring et al (2016) reported the development of a long-term EEP data set for CMIP6 model comparisons, which was derived from the MEPED measurements using the Ap magnetic index as a proxy (van de Kamp et al, 2016;Matthes et al, 2017). Andersson et al (2018) incorporated the CMIP6 EEP data set into a free-running version of WACCM to investigate polar ozone losses from MEE precipitation. They found MEE precipitation to have a significant impact on ozone loss in both the mesosphere and stratosphere.…”

Electron Precipitation From the Outer Radiation Belt During the St. Patrick's Day Storm 2015: Observations, Modeling, and Validation

“…Multiple earlier studies into the atmospheric and climate impacts of EEP have made use of directly observed POES EEP fluxes (Andersson et al, 2014;Newnham et al, 2018;Orsolini et al, 2018), albeit binned by time and latitude. The ApEEP model is more suitable for long climate runs than the direct POES EEP flux approach (Andersson et al, 2018), as the latter is limited to the time period of those direct observations. The ApEEP model incorporated in the CMIP6 project is suitable for climate modeling approaches back to 1850 and can be used in future climate model runs, using statistically predicted Ap values (Matthes et al, 2017).…”