Cooling of solar wind electrons inside 0.3 AU

Mean temperature gradients of solar wind electrons between 0.3 and 1 AU are determined from Helios observations. Electrons are found to cool more slowly than adiabatically, with flattest temperature profiles in high‐speed streams. These in situ observations are used to estimate the radial gradients of T e inside 0.3 AU under the constraint of matching coronal temperatures. Electrons in high‐speed streams are inferred to cool more strongly closer to the Sun than within the Helios orbital range. For low‐speed wind, no significant breaks in the temperature profiles have been found, while for intermediate‐speed structures the results are somewhat ambiguous. These results are discussed in the context of solar wind generation and modeling.