Self-consistent model of the interstellar pickup protons, Alfvenic turbulence, and core solar wind in the outer heliosphere
Gamayunov, Konstantin V.
Pogorelov, Nikolai V.
Rassoul, Hamid K.
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A self-consistent model of the interstellar pickup protons, the slab component of the Alfvénic turbulence, and core solar wind (SW) protons is presented for r ≥ 1 along with the initial results of and comparison with the Voyager 2 (V2) observations. Two kinetic equations are used for the pickup proton distribution and Alfvénic power spectral density, and a third equation governs SW temperature including source due to the Alfvén wave energy dissipation. A fraction of the pickup proton free energy, fD, which is actually released in the waveform during isotropization, is taken from the quasi-linear consideration without preexisting turbulence, whereas we use observations to specify the strength of the large-scale driving, Csh, for turbulence. The main conclusions of our study can be summarized as follows. (1) For Csh ≈ 1–1.5 and fD ≈ 0.7–1, the model slab component agrees well with the V2 observations of the total transverse magnetic fluctuations starting from ~8 AU. This indicates that the slab component at low-latitudes makes up a majority of the transverse magnetic fluctuations beyond 8–10 AU. (2) The model core SW temperature agrees well with the V2 observations for r gsim 20 AU if fD ≈ 0.7–1. (3) A combined effect of the Wentzel–Kramers–Brillouin attenuation, large-scale driving, and pickup proton generated waves results in the energy sink in the region r lesssim 10 AU, while wave energy is pumped in the turbulence beyond 10 AU. Without energy pumping, the nonlinear energy cascade is suppressed for r lesssim 10 AU, supplying only a small energy fraction into the k-region of dissipation by the core SW protons. A similar situation takes place for the two-dimensional turbulence. (4) The energy source due to the resonant Alfvén wave damping by the core SW protons is small at heliocentric distances r lesssim 10 AU for both the slab and the two-dimensional turbulent components. As a result, adiabatic cooling mostly controls the model SW temperature in this region, and the model temperature disagrees with the V2 observations in the region r lesssim 20 AU.