The Electron Temperature in the Two-Component Solar Wind

A systematic investigation of possible modifications in the equations of the two-fluid model for the solar wind, in order to predict, in addition to the other characteristics, the electron temperature and electron heat flow observed at 1 a.u., is carried out numerically. The equations used allow for a modified rate of energy exchange between electrons and protons as well as for modified electron and proton thermal conductivities. That is, these transport coefficients are allowed to include (besides collisional interactions) contributions from turbulent wave-particle interactions existing in the solar wind as well as effects due to inhibition across the interplanetary magnetic field. When the thermal equilibrium between electrons and protons is assumed to extend to a distance of 5-6 R0 away from the Sun, it is found that the agreement between the theoretical predictions and observations at 1 a.u. can be achieved in either one of the following two ways: (i) by using an energy-exchange rate about 30 times larger than the collisional one in conjunction with an electron thermal conductivity about 4 times lower than the collisional one; this provides (at 1 a.u.) flE = 6.33 cm ', VE = 256 km , = 1 6 X 10' K, TpE = 0.43 X 10' K, and -K ( ) = 0 75 X 10-2 ergs (ii) by using a proton thermal conductivity about twice the collisional one in conjunction with an electron thermal conductivity about 5 times lower than the collisional one; this provides flE = 6 cm ', VE = 270 km sec ', T = 1.59 X 10' K, T = 0.43 X 10' K, and -K (dTWdr) = 0 6 X 10-2 ergs cm sec '. It is suggested that additional measurements of the proton temperature at distances r >< 1 a.u. could help to determine the actual situation, which should probably be intermediate between the two possible ones described above.