Whistler mode turbulence in the disturbed solar wind

Abstract

Magnetic field fluctuations with frequencies f between the ion (fci) and electron (fce) cyclotron frequencies are enhanced downstream of interplanetary shocks and in fast streams. These f > fci fluctuations are related to those below fci that also accompany solar wind activity. The spectra over the range 10−2 fci ≤ f ≲ fce synthesized from ISEE 3 magnetometer and plasma wave instrument data can generally be described by one power law below f ≈ 1 Hz ≈ fci and a different one above. However, behind four shocks the spectral index above fci was measured to be about twice that below fci, whereas no clear relationship is apparent in the weaker fast stream events. Behind one shock the interference in the low‐frequency electric field channels of the ISEE 3 plasma wave instrument was small enough to permit a statistical study of the B/E ratios or, equivalently, the indices of refraction, of the fci ≤ f ≤ fce waves. Although the data base is limited, the B/E ratios confirm that the waves are whistler mode emissions, as their frequency range already suggested. Various indirect lines of evidence indicate that these whistler waves are generated propagating at large angles to the local interplanetary field, a fact that helps identify possible free energy sources for their growth.