Middle atmosphere response to the solar cycle in irradiance and ionizing particle precipitation
The impact of NO x and HO x 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 en-semble simulations forced by transient EPP derived from ob-servations 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 atmo-sphere in a significant way, bringing temperature and ozone variations closer to observed patterns. The Southern Hemi-sphere 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 cir-culation, with a weakening during solar maxima compared to solar minima. In response, the tropical tropopause tempera-ture 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.