Temperature anisotropy and differential streaming of solar wind ions. Correlations with transverse fluctuations

¹ Max-Planck-Institut für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany
e-mail: bourouaine@mps.mpg.de
² Institut für Geophysik und Meteorologie, Universität zu Köln, Albertus-Magnus-Platz, Köln 50923, Germany

Received: 10 August 2011
Accepted: 7 October 2011

Abstract

We study correlations of the temperature ratio (which is an indicator for perpendicular ion heating) and the differential flow of the alpha particles with the power of transverse fluctuations that have wave numbers between 0.01 and 0.1 (normalized to k_p = 1/l_p, where l_p is the proton inertial length). We found that both the normalized differential ion speed, V_αp/V_A (where V_A is the Alfvén speed) and the proton temperature anisotropy, T_⊥p/T_∥p, increase when the relative wave power is growing. Furthermore, if the normalized differential ion speed stays below 0.5, the alpha-particle temperature anisotropy, T_⊥α/T_∥α, correlates positively with the relative power of the transverse fluctuations. However, if V_αp/V_A is higher than 0.6, then the alpha-particle temperature anisotropy tends to become lower and attain even values below unity despite the presence of transverse fluctuations of relatively high amplitudes. Our findings appear to be consistent with the expectations from kinetic theory for the resonant interaction of the ions with Alfvén/ion-cyclotron waves and the resulting wave dissipation.