LENA Simulations

There have been a number of models producing differential fluxes of oxygen and hydrogen energetic neutral atoms or ENA, for short. The figures accesible from here include ENA produced by upflowing ions in the auroral zone, polar cap, and cleft ion fountain. The images on the left were produced by integrating along the line of sight from an observing point just beyond perigee in the nominal IMAGE orbit. The images on the right were constructed from those on the left by folding in the instrument response, which included the appropriate angular resolution and per pixel sensitivity, and adding random Poisson noise. The assumed geophysical conditions at the time of the image included high solar activity (F10.7=200). The model used to produce these images included ENA produced by upflowing ions from the cleft ion fountain, the auroral zone and the polar cap. The model also assumes the following:

  1. That the flux of ions coming from the ionosphere is proportional to the energy flux carried by precipitating electrons.
  2. That the total flux of O+ and H+ ions coming from the ionosphere is consistent with the results of Yau et al. [1988] and Pollock et al. [1990].
  3. A solution is found by launching many ions from the 1000 km source altitude and tracking them as they follow field lines, drifting due to the convection electric field and losing energy due to gravity.
  4. The ions begin life at 1000 km having velocities drawn from a perpendicularly heated biMaxwellian distribution.
  5. The magnetic field is assumed to be dipolar. The neutral atmosphere used is that given by the MSIS-86 model.
  6. The solution found is steady state and depends mainly on Kp and F10.7.

    7. Model ENA results
    hydrogen simulation hydrogen with instrument response
    oxygen simulation oxygen with instrument response