The cold solar wind

Abstract

From 3 to 10% of the time, the solar wind has a radial proton temperature between 15,000°K and 3500°K (the lowest recorded temperature). This “cold” component shows some very important features that make it worthy of special study. It shows a temperature dependence on heliocentric distance that is nearly adiabatic. When extrapolated back to 3 RS, assuming adiabatic cooling, the resulting temperature for this cold component is in good agreement with coronal temperatures near the sonic point. Most importantly, the proton velocities and densities associated with this cold component match those predicted by solar wind models that do not incorporate significant wave heating. We conclude that this is one solar wind component that fits well with appropriate models.