Solar cycle variations in the electron heat flux: Ulysses observations

Solar wind observations by the Ulysses spacecraft now include nearly ten years of continuous ion and electron measurements. In this study, we report detailed measurements of the electron heat flux in the solar wind. In particular, we examine the heat flux measurements for long-term correlations with wave activity and solar wind speed. We find that the average heat flux, when scaled by R-2.9 to account for variations due to distance from the Sun, is constant and independent of heliographic latitude or solar cycle. We find that during both solar maximum and solar minimum there is no significant correlation between the magnitude of the electron heat flux and the solar wind speed. Comparison of the electron heat flux data with wave activity indicates that the whistler heat flux instability does not play an important role in limiting the solar wind heat flux.