Abstract
Abstract. 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 which show a warming in the late winter upper stratosphere. In late winter and spring, the sign of the net radiative heating change turns to negative (effective cooling). This spring-time cooling lasts well into summer and continues until the following autumn after large solar proton events in the Southern Hemisphere, and after sudden stratospheric warmings in the Northern Hemisphere.
Highlights
Energetic particle precipitation is a potential contributor to the solar influence on the middle atmosphere, and has recently been recommended for the first time as a solar forcing parameter for the upcoming CMIP-6 model studies (Matthes et al, 2017)
When the impact of particle precipitation on total NOy, stratospheric ozone loss, and net radiative heating is determined from these models, it should be kept in mind that the indirect effect during Southern Hemisphere winters and Northern Hemisphere dynamically quiet winters will likely be underestimated by Karlsruhe Simulation of the Middle Atmosphere (KASIMA), but will likely be overestimated by 3dCTM and ECHAM/MESSy Atmospheric Chemistry (EMAC)
Ozone anomalies due to energetic particle precipitation only are derived from the model results as the difference of model runs with 3dCTM v1.6 phioniz, KASIMA v1.6, and EMAC upper boundary condition (UBC) to the respective Base model run without particle impacts
Summary
Energetic particle precipitation is a potential contributor to the solar influence on the middle atmosphere, and has recently been recommended for the first time as a solar forcing parameter for the upcoming CMIP-6 model studies (Matthes et al, 2017). High values of EPP NOx are observed in Northern Hemisphere late winters after the strong sudden stratospheric warming events in winters 2003/2004, 2005/2006, and 2008/2009 (Randall et al, 2006, 2009; Funke et al, 2014a; Sinnhuber et al, 2014; Funke et al, 2017) These warmings were followed by long-lasting downwelling in the mesosphere and upper stratosphere enabled by a strong polar vortex re-forming after the event. Analyses of observations using either geomagnetic activity or the hemispheric power index as proxies for particle precipitation suggest that such a coupling between EPP and atmospheric dynamics exists during polar winter, characterized by a warming of the mid to late winter upper stratosphere at high latitudes (Lu et al, 2008; Seppälä et al, 2013).
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have