Observation of the Heating and Acceleration of the Solar Wind by MHD Waves

The Poynting flux, measured on the Parker Solar Probe during 10 days surrounding the perihelion pass on April 4, 2019, was large (~20,000 μwatts/m²) at 35 solar radii and nearly zero before and after perihelion at 50 solar radii. Its spatial divergence means that electromagnetic energy was converted to plasma energy that heated and accelerated the solar wind. Because the Poynting flux, which is electromagnetic energy flow, was comparable in magnitude to the kinetic energy flow, 0.5nmv³, near perihelion, the Poynting flux was adequate for performing this acceleration task. Properties of the MHD waves that comprised the Poynting flux are discussed, including their correlation with magnetic field switchbacks.