Kyung Hee University, Yongin-si, Gyeonggi-do, 17104, Korea.
University of Warwick, Coventry CV4 7AL, United Kingdom.
Phys Rev Lett. 2018 Aug 17;121(7):075101. doi: 10.1103/PhysRevLett.121.075101.
Measurement of the solar wind speed near the Sun is important for understanding the acceleration mechanism of the solar wind. In this Letter, we determine 2D solar wind speeds from 6 to 26 solar radii by applying Fourier motion filters to SOHO/LASCO C3 movies observed from 1999 to 2010. Our method successfully reproduces the original flow speeds in the artificially generated data as well as streamer blobs. We measure 2D solar wind speeds from one-day to one-year timescales and their variation in solar cycle 24. We find that the solar wind speeds at timescales longer than a month in the solar maximum period are relatively uniform in the azimuthal direction, while they are clearly bimodal in the minimum period, as expected from the Ulysses observations and interplanetary radio scintillation reconstruction. The bimodal structure appears at around 2006, becomes most distinctive in 2009, and abruptly disappears in 2010. The radial evolution of the solar wind speeds resembles the Parker's solar wind solution.
测量太阳附近的太阳风速度对于理解太阳风的加速机制非常重要。在这封信中，我们通过应用傅里叶运动滤波器，从 1999 年至 2010 年 SOHO/LASCO C3 电影中确定了 6 到 26 个太阳半径处的二维太阳风速度。我们的方法成功地再现了原始数据中人工生成的流速度以及喷流斑。我们测量了一个日至一年时间尺度的二维太阳风速度及其在太阳活动周期 24 中的变化。我们发现，在太阳活动极大期的时间尺度超过一个月的情况下，太阳风速度在方位角方向上相对均匀，而在极小期则明显呈双峰结构，这与尤利西斯观测和行星际无线电闪烁重建的结果一致。双峰结构出现在 2006 年左右，在 2009 年最为明显，2010 年突然消失。太阳风速度的径向演化类似于帕克的太阳风解。
