Quasi-exospheric heat flux of solar-wind electrons

Density, bulk-velocity, and heat-flow moments are calculated for truncated maxwellian distributions representing the cool and hot populations of solar-wind electrons, as realized at the base of a hypothetical exosphere. The electrostatic potential is thus calculated by requiring charge quasineutrality and the absence of electrical current. Plasma-kinetic coupling of the cool-electron and proton bulk velocities leads to an increase in the electrostatic potential and a decrease in the heat-flow moment. If the velocities differ by the Alfvén speed along the magnetic field, for example, the potential rises to 72.6 V and the heat flux falls to 2.72×10^-2 erg cm^-2 s^-1. In each case the heat flux is carried mainly by the quasi-exospheric hot electrons.