Considerations that the source of auroral energetic particles is not a parallel electrostatic field

It is shown that electrostatic fields parallel (E₁₁) to the geomagnetic field cannot be the major mechanism that accelerates charged particles to auroral energies. Principal arguments are that electron and proton precipitation occur simultaneously, and also that precipitated electrons with energies less than 100 eV are found to accompany the electrons with energies of 1–10 keV that excite auroral luminosity. It is further shown that essentially all the ambient plasma in an entire tube of flux is required to sustain this intense low-energy precipitation, and this places a severe constraint on any replenishment process. It is found that generally the upper limit to (E₁₁) throughout the auroral regions of the ionosphere and magnetosphere is of order 10 μV/m and it may be appreciably less. Relevant measurements are reviewed briefly. It is concluded that while there may occasionally be significant E₁₁ fields, they play only a minor role-if any-in auroral phenomena.