Radiation Belt Electron Impact on Polar Atmospheric Ozone: a Simulation Study on Importance of Magnetic Local Time Dependency
Abstract
The radiation belts are regions in the near-Earth space where solar wind electrons are captured by the Earth's magnetic field. A part of these electrons is continuously lost into the atmosphere where they cause ionisation and chemical changes. Driven by the solar activity, electron forcing displays a decadal cycle which leads to ozone variability in the polar regions. Understanding possible dynamical connections to regional climate is an on-going research activity which supports the assessment of greenhouse gas driven climate change by better definition of the solar-driven variability. In the context of the Coupled Model Intercomparison Project Phase 6 (CMIP6) and the coming IPCC report, energetic electron and proton precipitation is included in the solar forcing recommendation for the first time. For radiation belt electrons, CMIP6 forcing is from a daily, zonal mean proxy model which is driven by the geomagnetic Ap index and provides a forcing data set extending back to 1850. This zonal mean model thus ignores the well-known dependency on magnetic local time (MLT), i.e. the diurnal variability. Here we use the Whole Atmosphere Community Climate Model with lower ionospheric chemistry extension (WACCM-D) to study the effect of MLT-dependency of electron forcing in polar ozone response. We analyse simulations with MLT-dependent and MLT-independent forcing, and contrast ozone responses in monthly mean data as well as in monthly means of individual local time sectors. We consider two cases: 1) year 2003 and 2) extreme, long-duration forcing. Our results indicate that the ozone responses to MLT-dependent and MLT-independent forcings are very similar, and the differences found are relatively small compared to overall uncertainties in electron forcing. Therefore, the fact that the CMIP6 electron forcing ignores MLT-dependency should not create any significant error in long-term climate simulations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSA33A..15V
- Keywords:
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- 0341 Middle atmosphere: constituent transport and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3334 Middle atmosphere dynamics;
- ATMOSPHERIC PROCESSES;
- 2716 Energetic particles: precipitating;
- MAGNETOSPHERIC PHYSICS;
- 2788 Magnetic storms and substorms;
- MAGNETOSPHERIC PHYSICS