Unravelling the Drivers of Energetic Electron Precipitation - Revealing the Imprint of Space on Earth (DEEP - RISE)

The sun is constantly emitting a wind of charged particles. The magnetic field in the solar wind will interact with the Earth’s magnetic field, driving different electromagnetic waves which increases the energy of the electrons and protons trapped in the Earth’s magnetic field. A fraction of these particles will collide with gasses in the atmosphere, and some will reach as low as 50 km altitude. The collisions will increase the production of NOx and HOx species, which in turn will reduce the ozone concentration. Ozone is important in the energy budget at these altitudes. Hence changing the concentration of ozone at 50 km might also impact temperature and winds. The winds have links to our weather system. It is therefore crucial to know the particle energy input and its altitude distribution to determine their effects on the atmosphere. The DEEP-RISE project has had a leading role in the international HEPPA III intercomparison study. It revealed the uncertainties in the available ionization rates and the associated impact on climate models. The ionization rates differed by about an order of magnitude both during geomagnetically quiet and disturbed periods. The study also revealed discrepancies on where the geographical impact of precipitation occurred. Consequently, we have created a model determining the latitudinal extent of energetic electron precipitation. Combined with the DEEP-RISE flux estimates, developed earlier in our project, the model have the potential to become a new EEP parameterization to be used for future studies of the energetic electron precipitation impact on the atmosphere. Moreover, the DEEP-RISE project has shown by running a climate model that when the atmosphere is dynamically unstable, even weak ionization rates are able influence temperature and winds down to 50 km. The result provides a first step in a paradigm shift for the understanding of the direct effect of energetic particle precipitation on the atmosphere.

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Energetic electrons precipitating from plasma sheet and the radiation belts surrounding the Earth, can collide with gases in the atmosphere and deposit their energy here. The depth to which they penetrate into the atmosphere depends on their initial energy. The collisions with atmospheric gasses initiate a number of chemical reactions leading to the production of odd nitrogen (NOX: N, NO, NO2) and odd hydrogen gasses (HOX: H, OH, HO2), which in turn can reduce the ozone concentration. Ozone is critically important in the energy budget in the middle atmosphere (50-80 km). Hence changing the concentration of ozone might impact temperature and winds at these altitudes, both of which links to our weather system. A reliable estimate of the electron energy input and its altitude distribution is therefore crucial for determining its effects on the atmosphere. Accurate quantification of energetic electron precipitation, however, remains to be obtained due to instrumental challenges. This imposes limitations of the associated EEP parameterisation into climate models. A solution to this problem is a better understanding of the driver processes of energetic electron acceleration and precipitation. Further, the radiation belts represent a hard environment for satellites, hence quantification of electron precipitation is also important for understanding the radiation belt variability due to loss to the atmosphere. These different perspectives are two sides of the same coin. Nonetheless, most researchers tend to focus on just one aspect, leaving out the potential added values for the other perspective. The motivation of the project is as follows: To achieve a holistic view on the causes of energetic electron precipitation and its dependence on solar wind structures and magnetospheric processes, to better estimate the occurrence, duration and strength of the energetic electron precipitation and the subsequent imprint on the atmosphere.