Interplanetary heat conduction: IMP 7 results

Heat flux conducted by coronal electrons is the dominant energy source which drives the solar wind. Both collisional and collisionless treatments of the solar-wind expansion problem predict the development of instabilities which are expected to lead to enhanced level of waves resulting in a reduction in plasma thermal conductivity. Experimental evidence consistent with the notion that the interplanetary heat flux is ''locally'' regulated by microinstabilities at 1 AU is reviewed. Briefly, the electron dimensionless third velocity moment is statistically independent of electron temperature and the electron heat flux appears to be nearly the same before and after abrupt connection to the earth's bow shock through the magnetic field. Furthermore, solar-wind electron-velocity distributions at 1 AU are observed to be, on the average, marginally stable with respect to the growth of electromagnetic ion cyclotron and/or magnetosonic waves