Solar cycle variations in the electron heat flux: Ulysses observations

Solar wind observations by the Ulysses spacecraft now include nearly ten ye ars of continuous ion and electron measurements. In this study, we report d etailed measurements of the electron heat flux in the solar wind. In partic ular, we examine the heat flux measurements for long-term correlations with wave activity and solar wind speed. We find that the average heat flux, wh en 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 fin d that during both solar maximum and solar minimum there is no significant correlation between the magnitude of the electron heat flux and the solar w ind speed. Comparison of the electron heat flux data with wave activity ind icates that the whistler heat flux instability does not play an important r ole in limiting the solar wind heat flux.