Title: Proton and electron temperatures in the solar wind and their correlations with the solar wind speed Show Chinese title

Title: 太阳风中的质子和电子温度及其与太阳风速度的相关性

Abstract: The heating and acceleration of the solar wind remains one of the fundamental unsolved problems in heliophysics. It is usually observed that the proton temperature $T_i$ is highly correlated with the solar wind speed $V_{SW}$, while the electron temperature $T_e$ shows anti-correlation or no clear correlation with the solar wind speed. Here we inspect both Parker Solar Probe (PSP) and WIND data and compare the observations with simulation results. PSP observations below 30 solar radii clearly show a positive correlation between proton temperature and wind speed and a negative correlation between electron temperature and wind speed. One year (2019) of WIND data confirm that proton temperature is positively correlated with solar wind speed, but the electron temperature increases with the solar wind speed for slow wind while it decreases with the solar wind speed for fast wind. Using a one-dimensional Alfv\'en-wave-driven solar wind model with different proton and electron temperatures, we for the first time find that if most of the dissipated Alfv\'en wave energy heats the ions instead of electrons, a positive $T_i-V_{SW}$ correlation and a negative $T_e-V_{SW}$ correlation arise naturally. If the electrons gain a small but finite portion of the dissipated wave energy, the $T_e-V_{SW}$ correlation evolves with radial distance to the Sun such that the negative correlation gradually turns positive. The model results show that Alfv\'en waves are one of the possible explanations of the observed evolution of proton and electron temperatures in the solar wind. Show Chinese abstract

Abstract: 太阳风的加热和加速仍然是日球物理学中尚未解决的基本问题之一。 通常观察到质子温度 $T_i$ 与太阳风速度 $V_{SW}$ 高度相关，而电子温度 $T_e$ 与太阳风速度呈反相关或无明显相关性。 在这里我们检查了帕克太阳探测器（PSP）和风号卫星（WIND）的数据，并将观测结果与模拟结果进行了比较。 PSP 在 30 个太阳半径以下的观测清楚地显示质子温度与太阳风速度之间存在正相关，而电子温度与太阳风速度之间存在负相关。 一年（2019年）的 WIND 数据证实质子温度与太阳风速度正相关，但电子温度对于慢速太阳风随太阳风速度增加，而对于快速太阳风则随太阳风速度减少。 利用一维阿尔芬波驱动的太阳风模型，该模型具有不同的质子和电子温度，我们首次发现，如果大部分耗散的阿尔芬波能量加热离子而不是电子，则正相关 $T_i-V_{SW}$ 和负相关 $T_e-V_{SW}$ 自然出现。 如果电子获得少量但有限的耗散波能量，则 $T_e-V_{SW}$ 相关会随着到太阳的径向距离变化，使得负相关逐渐变为正相关。 模型结果显示，阿尔芬波是解释太阳风中质子和电子温度演化的一个可能解释。