Solar Wind Acceleration

Abstract

AbstractThe general aspects of solar wind acceleration are well described by considering the thermally driven outflow from an electron – proton corona. However, two puzzling observations remain to be explained: 1) The predicted asymptotic flow velocity is much lower than that observed in high speed streams, and 2) The proton flux observed at 1AU varies considerably less than expected when considering the sensitivity of the proton flux to the coronal temperature predicted by thermally driven models. The solution of the first problem rests upon finding a mechanism which can deposit energy and/or momentum beyond the critical point of the flow. The invariance of the proton flux requires that a mechanism for maintaining a relatively constant proton density scale height in the subsonic region of the flow is found. One such possibility lies in considering the effects of an enhanced coronal helium abundance on the force balance of the subsonic flow. This scenario is discussed in some depth.