NO y production, ozone loss and changes in net radiative heating due to energetic particle precipitation in 2002–2010

• Published in: Atmospheric chemistry and physics 2018-01, Vol.18 (2), p.1115-1147
• Main Authors: Sinnhuber, Miriam, Berger, Uwe, Funke, Bernd, Nieder, Holger, Reddmann, Thomas, Stiller, Gabriele, Versick, Stefan, von Clarmann, Thomas, Wissing, Jan Maik
• Format: Article
• Language: English
• Subjects: Anomalies; Atmospheric chemistry; Atmospheric models; Atmospheric sounding; Auroral zones; Boundary conditions; Climate models; Computer simulation; Cooling; Cooling effects; Downwelling; Energetic particles; Evolution; Geomagnetic activity; Geomagnetism; Heating; Impact analysis; Interferometers; Ionization; Lower thermosphere; Mesosphere; Mixing ratio; Nitrogen budget; Nitrogen compounds; Northern Hemisphere; Oxides; Ozone; Particle precipitation; Polar winter; Precipitation; Protons; Radiation; Radiation belt electrons; Radiative cooling; Radiative heating; Solar maximum; Solar minimum; Solar protons; Solar storms; Southern Hemisphere; Spring; Stratosphere; Stratospheric temperatures; Stratospheric warming; Summer; Thermosphere; Upper stratosphere; Winter
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-18-1115-2018

We analyze the impact of energetic particle precipitation on the stratospheric nitrogen budget, ozone abundances and net radiative heating using results from three global chemistry-climate models considering solar protons and geomagnetic forcing due to auroral or radiation belt electrons. Two of the models cover the atmosphere up to the lower thermosphere, the source region of auroral NO production. Geomagnetic forcing in these models is included by prescribed ionization rates. One model reaches up to about 80 km, and geomagnetic forcing is included by applying an upper boundary condition of auroral NO mixing ratios parameterized as a function of geomagnetic activity. Despite the differences in the implementation of the particle effect, the resulting modeled NOy in the upper mesosphere agrees well between all three models, demonstrating that geomagnetic forcing is represented in a consistent way either by prescribing ionization rates or by prescribing NOy at the model top.Compared with observations of stratospheric and mesospheric NOy from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument for the years 2002–2010, the model simulations reproduce the spatial pattern and temporal evolution well. However, after strong sudden stratospheric warmings, particle-induced NOy is underestimated by both high-top models, and after the solar proton event in October 2003, NOy is overestimated by all three models. Model results indicate that the large solar proton event in October 2003 contributed about 1–2 Gmol (109 mol) NOy per hemisphere to the stratospheric NOy budget, while downwelling of auroral NOx from the upper mesosphere and lower thermosphere contributes up to 4 Gmol NOy. Accumulation over time leads to a constant particle-induced background of about 0.5–1 Gmol per hemisphere during solar minimum, and up to 2 Gmol per hemisphere during solar maximum. Related negative anomalies of ozone are predicted by the models in nearly every polar winter, ranging from 10–50 % during solar maximum to 2–10 % during solar minimum. Ozone loss continues throughout polar summer after strong solar proton events in the Southern Hemisphere and after large sudden stratospheric warmings in the Northern Hemisphere. During mid-winter, the ozone loss causes a reduction of the infrared radiative cooling, i.e., a positive change of the net radiative heating (effective warming), in agreement with analyses of geomagnetic forcing in stratospheric temperatures whi