REVISED MODEL OF THE STEADY-STATE SOLAR WIND HALO ELECTRON VELOCITY DISTRIBUTION FUNCTION

A recent study discussed the steady-state model for solar wind electrons during quiet time conditions. The electrons emanating from the Sun are treated in a composite three-population model-the low-energy Maxwellian core with an energy range of tens of eV, the intermediate similar to 10(2)-10(3) eV energy-range ("halo") electrons, and the high similar to 10(3)-10(5) eV energy-range ("super-halo") electrons. In the model, the intermediate energy halo electrons are assumed to be in resonance with transverse EM fluctuations in the whistler frequency range (similar to 10(2) Hz), while the high-energy super-halo electrons are presumed to be in steady-state wave-particle resonance with higher-frequency electrostatic fluctuations in the Langmuir frequency range (similar to 10(5) Hz). A comparison with STEREO and WIND spacecraft data was also made. However, ignoring the influence of Langmuir fluctuations on the halo population turns out to be an unjustifiable assumption. The present paper rectifies the previous approach by including both Langmuir and whistler fluctuations in the construction of the steady-state velocity distribution function for the halo population, and demonstrates that the role of whistler-range fluctuation is minimal unless the fluctuation intensity is arbitrarily raised. This implies that the Langmuir-range fluctuations, known as the quasi thermal noise, are important for both halo and super-halo electron velocity distribution.