Solar Wind Energy Flux Observations in the Inner Heliosphere: First Results from Parker Solar Probe

Abstract:

The Parker Solar Probe (PSP) mission, launched on August 12th, 2018, is a historical mission to probe the solar corona. The heliocentric distances of PSP's perihelia of elliptical trajectories are designed to decrease from 35.7 solar radii (Rs) to 9.86 Rs. In particular, this gives us an opportunity to study the solar wind energy flux in the inner heliosphere, which is of great importance to determine the acceleration of the solar wind at the base of the corona. With the electron parameters (density n_e, core electron temperature T_ce, and halo electron temperature T_he) obtained from the simplified analysis of the plasma quasi-thermal noise (QTN) spectrum measured by RFS/FIELDS and the bulk proton parameters (density n_p, bulk velocity V_p, and temperature T_p) measured by SPC/SWEAP, we calculate the solar wind energy flux using 12-day observations around each perihelion of Encounter One (E01), Two (E02) and Four (E04) of PSP, respectively. The corresponding heliocentric distance ranges from 27.8 to 55.0 Rs. Combining E01, E02 and E04, the averaged energy flux value normalized to 1 Rs is about 70 W.m^-2, which is in agreement with the average value (~79 W.m^-2) derived from the long-term observations by Le Chat et al., 2012. The solar wind energy flux is calculated based on the assumption that the ratio of the alpha density to the electron density n_a/n_e ranges from 1% to 4%, leading to an uncertainty less than 10%. The average value of the energy flux increases with the n_a/n_e ratio. Latest PSP observations will be taken into account to give an updated value.