000005700 001__ 5700
000005700 005__ 20220315142231.0
000005700 0247_ $$2DOI$$a10.3847/1538-4357/ac1067
000005700 037__ $$aSCART-2022-0048
000005700 100__ $$aMicera, Alfredo
000005700 245__ $$aOn the Role of Solar Wind Expansion as a Source of Whistler Waves: Scattering of Suprathermal Electrons and Heat Flux Regulation in the Inner Heliosphere
000005700 260__ $$c2021
000005700 520__ $$aThe role of solar wind expansion in generating whistler waves is investigated using the EB-iPic3D code, which models solar wind expansion self-consistently within a fully kinetic semi-implicit approach. The simulation is initialized with an electron velocity distribution function modeled after observations of the Parker Solar Probe during its first perihelion at 0.166 au, consisting of a dense core and an antisunward strahl. This distribution function is initially stable with respect to kinetic instabilities. Expansion drives the solar wind into successive regimes where whistler heat flux instabilities are triggered. These instabilities produce sunward whistler waves initially characterized by predominantly oblique propagation with respect to the interplanetary magnetic field. The excited waves interact with the electrons via resonant scattering processes. As a consequence, the strahl pitch angle distribution broadens and its drift velocity reduces. The strahl electrons are scattered in the direction perpendicular to the magnetic field, and an electron halo is formed. At a later stage, resonant electron firehose instability is triggered and further affects the electron temperature anisotropy as the solar wind expands. Wave-particle interaction processes are accompanied by a substantial reduction of the solar wind heat flux. The simulated whistler waves are in qualitative agreement with observations in terms of wave frequencies, amplitudes, and propagation angles. Our work proposes an explanation for the observations of oblique and parallel whistler waves in the solar wind. We conclude that solar wind expansion has to be factored in when trying to explain kinetic processes at different heliocentric distances.
000005700 594__ $$aNO
000005700 700__ $$aZhukov, Andrei
000005700 700__ $$aLópez, Rodrigo
000005700 700__ $$aBoella, Elisabetta
000005700 700__ $$aTenerani, Anna
000005700 700__ $$aVelli, Marco
000005700 700__ $$aLapenta, Giovanni
000005700 700__ $$aInnocenti, Maria Elena
000005700 773__ $$pThe Astrophysical Journal$$y2021
000005700 8560_ $$falfredo.micera@observatoire.be
000005700 905__ $$apublished in
000005700 980__ $$aREFERD