About the project
The objective of this project was to investigate solar-terrestrial coupling associated to energetic particle precipitation and its influence on the chemistry and dynamics of the upper and middle atmosphere, as well as on climate at high latitudes.
In addition to its radiative output, the Sun emits particles (mostly electrons and protons) which can reach the Earth's atmosphere, depositing their energy in the thermosphere and middle atmosphere. This energetic particle precipitation (EPP) into the atmosphere produces dissociation and ionization, initiating a series of neutral and ionic chemical reactions, which result in the production of short-lived hydrogen oxides and longer-lived nitric oxides (NOx). In the dark conditions of the winter high latitudes, NOx can have an effective lifetime of months, and descend into the upper stratosphere, where it drives the main catalytic cycle of ozone destruction. Perturbations of the ozone composition can affect temperature and winds, not only in the stratosphere but also potentially into the troposphere and at the surface.
The efficiency of this process is partly dependent on the particle energy input, and partly dependent on the background middle atmosphere dynamics. For example, events like sudden stratospheric warmings, while initiated by planetary waves propagating from below, are associated with large descent of NOx from the upper-atmospheric reservoir. Transport of sufficient NOx from the high-altitude reservoir into the lower atmosphere is central for a chemistry-climate model to represent the indirect effect from EPP on stratospheric composition and dynamics. Several recent case studies point out that chemistry-climate models are still deficient in that respect, hindering a full representation of the solar impact upon climate.
While the influence of energetic particle precipitation has largely been neglected in the context of climate change in the past, the Intergovernmental Panel on Climate Change (IPPC) newest assessment (CMIP6) is the first one to include particle precipitation including influence from both precipitating protons and medium-energy electrons (MEE), in coupled (ocean-atmosphere) climate models. While the influence of the large but rare proton precipitation events has been explored with chemistry-climate models for years, the effects of the more frequent energetic electron precipitation (EEP) events are poorly understood, both in observations and models.
Project leader
Yvan Orsolini, Norwegian Institute for Air Research (NILU)
Financing
The Research Council of Norway, RCN.