Do plasma wave instabilities coexist with strong plasma turbulence in the solar wind?

Investigations of the normalized magnetic helicity spectrum in high speed solar wind as a function of the angle θ_BV formed by the local mean magnetic field and the solar wind flow velocity show evidence of two separate populations of electromagnetic fluctuations at wavenumbers near the proton gyro-radius kρ_i ~ 1. These two populations are evidenced by the different algebraic sign of the normalized magnetic helicity observed when the local mean magnetic field is oriented either parallel or perpendicular to the flow direction of the solar wind, that is, near θ_BV= 0 or π/2. The fluctuations observed when θ_BV≈ π/2 have tentatively been identified as kinetic Alfven fluctuations or kinetic Alfven waves (KAWs) with quasi-perpendicular wave vectors, k_⊥>> k_∥, consistent with the existence of a turbulent energy cascade supported by strong Alfvenic turbulence at MHD scales and an eventual transition to strong kinetic Alfven turbulence at kinetic scales. The fluctuations observed near θ_BV= 0 have tentatively been identified as quasi-parallel propagating electromagnetic ion-cyclotron waves traveling away from the sun or quasi-parallel propagating magnetosonic-whistler waves traveling toward the sun along the local mean magnetic field. Existing in-situ data is insufficient to uniquely identify the parallel propagating modes. A natural explanation for the observed parallel propagating waves is provided by the proton temperature anisotropy instability in the presence of a subpopulation of alpha particles that flow faster than the protons away from the sun along the magnetic field. This instability generates ion-cyclotron waves propagating predominantly away from the sun when T_p⊥> T_p∥ and magnetosonic-whistler waves propagating predominantly toward the sun when T_p⊥< T_p∥. Moreover, the predicted frequencies and wavenumbers of the unstable modes agree reasonably well with observations. One possible objection to this interpretation is that the linear Vlasov-Maxwell wave theory applies to a quiescent plasma in a quasi-equilibrium state whereas the solar wind is usually in a turbulent state. This raises the important question: Can plasma wave instabilities exist in the presence of strongly nonlinear turbulence? If the answer is yes, then how should the Vlasov-Maxwell wave theory be modified to correctly analyze the instability? If the answer is no, then what is the source of the parallel propagating waves observed near the ion inertial length in the solar wind? Are these parallel waves somehow generated by turbulent dissipation processes? If so, then how? These and other questions shall be addressed in this presentation.