Abstract
Abstract. The impact of NOx and HOx production by three types of energetic particle precipitation (EPP), auroral zone medium and high energy electrons, solar proton events and galactic cosmic rays on the middle atmosphere is examined using a chemistry climate model. This process study uses ensemble simulations forced by transient EPP derived from observations with one-year repeating sea surface temperatures and fixed chemical boundary conditions for cases with and without solar cycle in irradiance. Our model results show a wintertime polar stratosphere ozone reduction of between 3 and 10 % in agreement with previous studies. EPP is found to modulate the radiative solar cycle effect in the middle atmosphere in a significant way, bringing temperature and ozone variations closer to observed patterns. The Southern Hemisphere polar vortex undergoes an intensification from solar minimum to solar maximum instead of a weakening. This changes the solar cycle variation of the Brewer-Dobson circulation, with a weakening during solar maxima compared to solar minima. In response, the tropical tropopause temperature manifests a statistically significant solar cycle variation resulting in about 4 % more water vapour transported into the lower tropical stratosphere during solar maxima compared to solar minima. This has implications for surface temperature variation due to the associated change in radiative forcing.
Highlights
The field of research on the influence of the variability of solar radiation and particle flux on the atmosphere is fast growing, great uncertainty remains concerning impacts and the mechanisms involved
Modeling studies of solar variability effects on the climate system have focused on two basic ideas: (1) direct forcing of the troposphere by surface warming associated with changes in the total solar irradiance (TSI) or, in a more complex scenario, modulation of the atmosphere-ocean interactions producing internal oscillations; and (2) forcing of the stratosphere associated with changes in ultraviolet (UV) radiation causing an increase in ozone and associated warming during solar maximum conditions
The magnitude of and in the troposphere shows a statistically significant differthe dynamical perturbation from the ozone loss in this region ence pattern that resembles the one identified by Polvani and is comparable for each of the individual energetic particle precipitation (EPP) simulations and Kushner (2002). This tropospheric change in the zonal wind the combined EPP simulation, the structure differs. was apparent in the runs for the individual EPP types as well. This is supported by the weak non-additivity of the ozone In the ensemble run, the SH polar vortex showed some defield seen in Fig. 8, which indicates that the nonlinear dynamical response to the ozone perturbations satgree of weakening below 30 km in all members
Summary
The field of research on the influence of the variability of solar radiation and particle flux on the atmosphere is fast growing, great uncertainty remains concerning impacts and the mechanisms involved. Little effort was devoted to the inclusion of EPP effects in chemistry climate models partly due to complexity and since they were considered to be of secondary importance on climate timescales This has changed in recent years prompted by conclusive observational evidence of significant NOx enhancement in the polar regions, extending to stratospheric altitudes, during major solar proton events (e.g., Siskind, 2000; Randall et al, 2001, 2005; Hauchecorne et al, 2005, 2007; Jackman et al, 2005; Lopez-Puertas et al, 2005). 4. To address dynamical variability effects, a three-member ensemble simulation without the solar irradiance cycle but with all three EPP types included was produced and is presented in Sect.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
