Abstract
<div> <div> <div> <p>The radiation belts are regions in the near-Earth space where solar wind electrons are captured by the Earth’s magnetic field. A portion of these electrons is continuously lost into the atmosphere where they cause ionization and chemical changes. Driven by the solar activity, the electron forcing leads to ozone variability in the polar stratosphere and mesosphere. Understanding the possible dynamical connections to regional climate is an ongoing research activity which supports the assessment of greenhouse-gas-driven climate change by a better definition of the solar-driven variability. In the context of the Coupled Model Intercomparison Project Phase 6 (CMIP6), energetic electron and proton precipitation is included in the solar-forcing recommendation for the first time. For the radiation belt electrons, the CMIP6 forcing is from a daily zonal-mean proxy model. This zonal-mean model ignores the well-known dependency of precipitation on magnetic local time (MLT), i.e. its diurnal variability. Here we use the Whole Atmosphere Community Climate Model with its lower-ionospheric-chemistry extension (WACCM-D) to study effects of the MLT dependency of electron forcing on the polar-ozone response. We analyse simulations applying MLT-dependent and MLT-independent forcings and contrast the resulting ozone responses in monthly-mean data as well as in monthly means at individual local times. We consider two cases: (1) the year 2003 and (2) an extreme, continuous forcing. Our results indicate that the ozone responses to the MLT-dependent and the MLT-independent forcings are very similar, and the differences found are small compared to those caused by the overall uncertainties related to the representation of electron forcing in climate simulations. We conclude that the use of daily zonal-mean electron forcing will provide an accurate ozone response in long-term climate simulations.</p> </div> </div> </div>
Highlights
Energetic particle precipitation (EPP) and its impact on middle-atmospheric polar ozone is recognized as a potential driver for dynamical connections between space weather and regional climate variability (Andersson et al, 2014, and references therein)
Since the APEEP models are designed to be used in multi-decadal climate simulations such as those conducted during Coupled Model Intercomparison Project Phase 6 (CMIP6), it is more interesting to ask if the analysis of such simulations gives different answers if the MLTdependent APEEP forcing is applied
We consider different local solar times (LSTs) separately from hourly output data saved separately. This would be similar to the analysis of data from polar-orbiting satellites, since such measurements are typically made at limited local times for any given latitude
Summary
Energetic particle precipitation (EPP) and its impact on middle-atmospheric polar ozone is recognized as a potential driver for dynamical connections between space weather and regional climate variability (Andersson et al, 2014, and references therein). In the CMIP6 EPP data set, the ionization rates due to mid-energy electrons (MEEs) have been calculated using a precipitation model driven by the geomagnetic Ap index (van de Kamp et al, 2016). This model is based on electron flux observations of the Medium-Energy Proton and Electron Detectors (MEPED) flying aboard the Polar-orbiting Operational Environmental Satellites (POES). Due to the complexity of factors affecting ozone depletion, it is not clear if results of such an analysis are significantly dependent on the diurnal variability of the EPP forcing Assessing this would be essential because an accurate representation of middle-atmospheric ozone is crucially needed in climate simulations, e.g. to initiate the dynamical coupling with the troposphere (Andersson et al, 2014). We analyse the monthly-mean results as well as the monthly averages at different local times and discuss the differences in the ozone impact in the context of overall uncertainties in the MEE forcing
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