Nonthermal heating in the two‐fluid solar wind model

The two‐fluid solar wind model predicts values for wind speed and proton temperature that are lower than average observed values; however, the predictions are consistent with the empirical relation of Burlaga and Ogilvie, in which the square root of the proton temperature is proportional to the wind speed. Since observed values of wind speed and proton temperature are typically higher than those of the two‐fluid model, it is concluded that energy must be supplied by dissipation of nonthermal energy from an external source. The two‐fluid model is therefore extended by including ad hoc an energy source in the proton heat equation whose strength and spatial distribution is varied to determine the general requirements of such a source. The main features of our results are: Heat deposited inside the heliocentric radius r ≃4 R s results in a significant increase in wind speed with negligible increase in proton temperature. Depositing heat over the range r ≳25 R s results in a large increase in proton temperature and negligible increase in wind speed. By depositing heat over the extended range 2 R s ≲ r ≲25 R s , solar wind speeds and proton temperatures can be brought into direct correspondence with the empirical results of Burlaga and Ogilvie. On the basis of this model, we conclude that primary energy deposition should take place inside r ≃25 R s .