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According to emph{Wind} observations between June 2004 and May 2019, this Letter investigates the proton and alpha particle temperatures in the space of ($theta_d$, $V_d/V_A$) for the first time, where $theta_d$ and $V_d$ are the radial angle and magnitude of alpha$-$proton differential flow vector respectively, $V_A$ is the local Alfven speed. Results show that the temperatures significantly depend on $theta_d$ as well as $V_d/V_A$. In case of low proton parallel beta ($beta_{p{parallel}} < 1$), it is found that the proton perpendicular temperature is clearly enhanced when $theta_d$ is small ($lesssim 45^circ$) and $V_d/V_A gtrsim 0.5$. On the contrary, the perpendicular temperature of alpha particles is considerably enhanced when $theta_d$ is large ($gtrsim 90^circ$) or $V_d/V_A$ is sufficiently small. The maximum of proton parallel temperature takes place at $theta_d sim 90^circ$ accompanied by higher $beta_{p{parallel}}$ and by larger turbulence amplitude of magnetic fluctuations in inertial range. This study should present strong evidence for cyclotron resonance heating of protons and alpha particles in the solar wind. Other mechanisms including Landau resonance and stochastic heating are also proposed, which tend to have different ($theta_d$, $V_d/V_A$) spaces than cyclotron resonance heating.
Plasma kinetic waves and alpha-proton differential flow are two important subjects on the topic of evolution of the solar wind. Based on the Wind data during 2005-2015, this paper reports that the occurrence of electromagnetic cyclotron waves (ECWs)
Based on in-situ measurements by Wind spacecraft from 2005 to 2015, this letter reports for the first time a clearly scale-dependent connection between proton temperatures and the turbulence in the solar wind. A statistical analysis of proton-scale t
The solar wind undergoes significant heating as it propagates away from the Sun; the exact mechanisms responsible for this heating are not yet fully understood. We present for the first time a statistical test for one of the proposed mechanisms, stoc
Evidence for inhomogeneous heating in the interplanetary plasma near current sheets dynamically generated by magnetohydrodynamic (MHD) turbulence is obtained using measurements from the ACE spacecraft. These coherent structures only constitute 19% of
We investigate the spatial correlation properties of the solar wind using simultaneous observations by the ACE and WIND spacecraft. We use mutual information as a nonlinear measure of correlation and compare this to linear correlation. We find that t