Transient Solar Events and Space Weather
Solar variability is an important source of natural climate variability. The Aurora is a wonderful display of the impact of energetic particles on the upper atmosphere.
Energetic particles can also produce nitric oxides, that, when transported into the middle atmosphere, provide a coupling mechanism between solar variability, space weather and the middle atmosphere.
With the solar activity expected to decline during the coming decades, the assessment of solar influences on temperature and composition of the middle atmosphere is crucial for identifying the natural forcing contribution to long-term climate variability. One aspect of solar activity is Energetic Particle Precipitation (EPP), either directly by coronal mass ejections producing sporadically large fluxes of solar energetic particles or indirectly by the quasi-continuous, but highly variable, impact of the solar wind on the Earth’s magnetosphere. EPP causes enhanced ionisation in the polar upper mesosphere and lower thermosphere leading to the formation of nitric oxides. These can be transported down, affecting the stratospheric ozone layer, and potentially interfering with polar ozone recovery. This, in turn, can affect the regional weather systems in mid-to high latitudes. EPP is therefore recognized as an integral part of the solar climate forcing.