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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, stochastic ion heating. We use the amplitude of magnetic field fluctuations near the proton gyroscale as a proxy for the ratio of gyroscale velocity fluctuations to perpendicular (with respect to the magnetic field) proton thermal speed, defined as $epsilon_p$. Enhanced proton temperatures are observed when $epsilon_p$ is larger than a critical value ($sim 0.019 - 0.025$). This enhancement strongly depends on the proton plasma beta ($beta_{||p}$); when $beta_{||p} ll 1$ only the perpendicular proton temperature $T_{perp}$ increases, while for $beta_{||p} sim 1$ increased parallel and perpendicular proton temperatures are both observed. For $epsilon_p$ smaller than the critical value and $beta_{||p} ll 1$ no enhancement of $T_p$ is observed while for $beta_{||p} sim 1$ minor increases in $T_{parallel}$ are measured. The observed change of proton temperatures across a critical threshold for velocity fluctuations is in agreement with the stochastic ion heating model of Chandran et al. (2010). We find that $epsilon_p > epsilon_{rm crit}$ in 76% of the studied periods implying that stochastic heating may operate most of the time in the solar wind at 1 AU.
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 mag
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
A model-independent first-principle first-order investigation of the shape of turbulent density-power spectra in the ion-inertial range of the solar wind at 1 AU is presented. De-magnetised ions in the ion-inertial range of quasi-neutral plasmas resp
The scaling of the turbulent spectra provides a key measurement that allows to discriminate between different theoretical predictions of turbulence. In the solar wind, this has driven a large number of studies dedicated to this issue using in-situ da
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