The three‐dimensional raman's distribution as a non‐Maxwellian model and the ionospheric ion outflows into the magnetosphere revisited

Abstract

The three‐dimensional Raman's distribution as a model for fitting non‐Maxwellian distributions, and the consequences for the hydrodynamic mirror force due to coupling between pressure anisotropy and the inhomogeneous geomagnetic field are revisited. We demonstrate that the three‐dimensional Raman's model is unable to quantitatively predict the Post‐Rosenbluth or ion cyclotron instability threshold. The application of this model to deduce ion temperature anisotropy from only one radar spectra measurement is shown to be restricted to specific aspect angles and small electric field intensities. This model provides the line‐of‐sight temperature and then the thermodynamical temperature for aspect angle equal to 54.7°. The hydrodynamic upwelling force is shown to be greatly affected by the ion‐neutral interaction process. This additional force represents an important amount of the gravity in the presence of large electric fields. The upwelling force is overestimated to a great extent, when using the three‐dimensional Raman's model to fit non‐Maxwellian distribution functions observed in the auroral ionosphere.