Theoretical predictions of the effect of cusp and dayside precipitation on the polar ionosphere


  • Aurélie Vontrat-Reberac,

  • Dominique Fontaine,

  • Pierre-Louis Blelly,

  • Marina Galand


We use the numerical model TRANSCAR to investigate the signature of cusp electron and proton precipitation on all ionospheric parameters (electron density, electron and ion temperatures, and ion field-aligned velocity) and to compare it to that of other precipitation source regions expected in the dayside polar ionosphere, such as the low-latitude boundary layer or the dayside extension of the plasma sheet. If the precipitating energetic protons contribute to the formation of a strong density peak in the E region, similarly to the auroral zone, the low-energy electrons are responsible for very different features. For example, they produce density enhancements in F and low F regions which even increase in time owing to a buildup effect induced by the long timescales in this altitude range. We have estimated that cusp electron precipitations heat the ambient electron gas by typically 750–1000 K and induce much larger temperatures than precipitations from any other source regions. One striking feature is the ion upward flows that can reach values up to 250 m s−1 or more, well above those obtained from the other source regions. Finally, the electron density enhancement initially produced by cusp precipitation persists for timescales of the order of hours after the precipitation event owing to the long timescales at F region altitudes. Combined with transport processes, this effect may supply ionization to other regions of the polar or auroral ionosphere.