Trans-coronal radio observations were taken during the 2011 observing campaign of the Akatsuki spacecraft through superior conjunction. The observed X-band (8.4 GHz) signals exhibit frequency fluctuations (FF) that are produced by temporal variations in electron density along the radio ray path. A two-component model for interpretation of the FF is proposed: FF scales largely with acoustic wave amplitude through the inner coronal regions where the sound speed dwarfs the solar wind outflow speed, while FF in the region of solar wind acceleration is dominated by the increased density oscillation frequency on the sensing path that results from bulk advection of the plasma inhomogeneities. An estimate of fractional electron density fluctuation is obtained from the mid-corona. A radial profile of slow solar wind speed is determined in the extended corona using mass-flux continuity principles. The coronal sonic point for slow solar wind is estimated to range from 4 to 5 solar radii from the heliocenter.

中文翻译：

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从 Akatsuki 航天器无线电观测推断的日冕电子密度波动

跨日冕无线电观测是在 2011 年 Akatsuki 航天器观测活动期间通过上合相进行的。观察到的 X 波段 (8.4 GHz) 信号表现出频率波动 (FF)，这是由沿无线电射线路径的电子密度的时间变化产生的。提出了一个用于解释 FF 的双分量模型：FF 在声速使太阳风外流速度相形见绌的内日冕区域很大程度上与声波幅度成比例，而在太阳风加速度区域中的 FF 主要受增加的感应路径上的密度振荡频率是由等离子体不均匀性的整体平流引起的。分数电子密度波动的估计是从中间日冕中获得的。使用质量通量连续性原理在扩展日冕中确定慢太阳风速的径向轮廓。慢太阳风的日冕声波点估计在距日心 4 到 5 个太阳半径的范围内。