Estimates of solar wind heating inside 0.3 AU

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Abstract
We normalize the Helios 1 proton temperature data to 0.3 AU to establish a base temperature‐velocity curve at that distance and ask what solar wind heating rates, versus velocity, closer to the sun, are required to predict that curve. The results indicate that the slope of the solar wind temperature gradient for high‐speed streams, inside 0.3 AU, is about half of that found beyond this distance. The very low‐speed wind on the other hand is found to expand adiabatically all the way out. Intermediate speed winds have enhanced heating rates in proportion to their velocities.