A model for generation of bow-shock-associated upstream waves

It is shown that proton streams reflected from a bow shock structure that partially organizes their distribution in gyrophase in such a way that the reflected beam distribution function has the form F_b(υ_⊥², υ_∥, ϕ), where ϕ is the phase angle for motions perpendicular to the solar wind field B_o, are capable of driving a left-hand (Alfvén) wave at rest frame frequencies ω < Ω_ı. The driven wave amplitude becomes a sharply peaked function of ω/Ω_ı = x, and the location x = x_o and peak amplitude of the wave B(x_o) depend critically on the ratio of beam speed V_b to the Alfvén speed C_A and on the value of solar wind β. Driven wave amplitudes are estimated to be up to several gammas for beam speeds (in the rest frame) of V_b ∼ 2V_SW. The observed frequency and polarization depend upon Doppler shifting due to solar wind flow, and observed polarization could be either left-hand or right-hand depending upon the vector properties of the solar wind velocity and magnetic fields.