Sonic and Alfvenic Critical Point and the Solar Probe Mission: presentation to the Solar Probe Science and Technology Definition Team

Are critical points important in the Solar Probe Mission? This is a brief discussion of the nature of critical points in solar wind models, what this means physically in the 'real' solar wind, and what can be expected along a nominal Solar Probe Orbit. The conclusion is that the regions where the wind becomes transonic and trans-Alfvenic, which may be irregular and varying, may reveal interesting physics, but the mathematically defined critical points themselves are of less importance.