POSSIBLE EVIDENCE OF ALFVÉN-CYCLOTRON WAVES IN THE ANGLE DISTRIBUTION OF MAGNETIC HELICITY OF SOLAR WIND TURBULENCE

Abstract

The fluctuating magnetic helicity is considered an important parameter in diagnosing the characteristic modes of solar wind turbulence. Among them is the Alfv?n-cyclotron wave, which is probably responsible for the solar wind plasma heating, but has not yet been identified from the magnetic helicity of solar wind turbulence. Here, we present the possible signatures of Alfv?n-cyclotron waves in the distribution of magnetic helicity as a function of ?VB, which is the angle between the solar wind velocity and local mean magnetic field. We use magnetic field data from the STEREO spacecraft to calculate the ?VB distribution of the normalized reduced fluctuating magnetic helicity ?m. We find a dominant negative ?m for 1 s 150? in the solar wind inward magnetic sector. These features of ?m appearing around the Doppler-shifted ion-cyclotron frequencies may be consistent with the existence of Alfv?n-cyclotron waves among the outward propagating fluctuations. Moreover, right-handed polarized waves at larger propagation angles, which might be kinetic Alfv?n waves or whistler waves, have also been identified on the basis of the ?m features in the angular range 40? < ?VB < 140?. Our findings suggest that Alfv?n-cyclotron waves (together with other wave modes) play a prominent role in turbulence cascading and plasma heating of the solar wind.