Are Whistler Waves Regulating the Electron Heat Flux in the Solar Wind at 1 AU ? Wind Observations.

Electron heat conduction provides a major means of energy transport in collisionless plasmas. Yet, the mechanisms which determine the electron energy transport and dissipation in the solar wind are far from being understood. The electron heat flux is observed to be actively dissipated as the solar wind expands into interplanetary space, and neither collisionless expansion along the interplanetary magnetic field nor collision dominated thermal transport can well describe the average observed value of the electron heat flux at a given heliocentric distance. Besides Coulomb collisions, whistler wave-particle interactions have been suggested as an other possible source of the dissipation necessary to regulate the electron heat flux. Using high-time resolution particle and wave data from the WIND spacecraft, we analyze here the electron heat flux in relation to the level of whistler-like magnetic field fluctuations, during 50 days close to the last minimum of solar activity. We show that WIND observations lead to the conclusion that whistler waves are likely to play a role in the regulation of the heat flux in the solar wind, while recent Ulysses observations were not conclusive on this point.