Observation of the Solar Corona Using Radio Scintillation with the Akatsuki Spacecraft: Difference Between Fast and Slow Wind
Observation of the Solar Corona Using Radio Scintillation with the Akatsuki Spacecraft: Difference Between Fast and Slow Wind
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使用“晓”号宇宙飞船的射电闪烁观测日冕：快风和慢风的区别
DOI：
10.1007/s11207-022-01968-9
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发表时间：
2022
期刊：
影响因子：
2.8
通讯作者：
P?tzold Martin
中科院分区：
文献类型：
--
作者：
Chiba Shota;Imamura Takeshi;Tokumaru Munetoshi;Shiota Daikou;Matsumoto Takuma;Ando Hiroki;Takeuchi Hiroshi;Murata Yasuhiro;Yamazaki Atsushi;H?usler Bernd;P?tzold Martin
2016年，利用日本宇宙航空研究开发机构（JAXA）的akatsukisspacecraft进行了射电掩星观测，研究了日心距离为1.5 - 8.9（太阳半径）的日冕等离子体的特性。通过将理论谱与观测功率谱拟合，从强度闪烁时间序列中获取表征太阳风的物理参数。推导的太阳风速度清晰地显示了快风和慢风之间的差异，这是基于IPS观测确定的。流体运动耗散和动能转化为热能的内尺度随着日心距离的增加而增大，且快风的内尺度大于慢风。通过对频率时间序列进行小波分析，我们检测到了电子密度的准周期波动。密度振荡被认为是声波的表现，声波是由光球产生的alfvsamn波产生的，并估计了这些声波的能量通量。相对密度振幅在4 ~ 6附近达到峰值，波能通量在≈6以上减小，表明声波在日冕附近消散并加热日冕。我们得到的相位闪烁谱不能用一个幂律来表示。超过≈6的0.5 - 2hz频率附近出现中断，表明在较低频率时除了湍流之外还有多余的功率。小波分析发现，相对密度振幅在6附近的增强可能解释了这种过剩功率。快速太阳风中的声波能量通量倾向于超过慢风中的声波能量通量，这表明快速太阳风比慢风注入更多的阿尔夫萨芬波能量。
The properties of the coronal plasma at heliocentric distances of 1.5 – 8.9(solar radii) were studied with radio-occultation observations using JAXA’sAkatsukispacecraft in 2016. Physical parameters that characterize the solar wind were retrieved from the intensity-scintillation time series by fitting a theoretical spectrum to the observed power spectra. The derived solar-wind velocity clearly shows a difference between the fast wind and the slow wind, which was identified based on IPS observations. The inner scale, at which fluid motions dissipate and kinetic energy is converted to heat, increases with the heliocentric distance, and the fast wind has larger inner scales than the slow wind. By applying wavelet analysis to the frequency time series, we detected quasi-periodic fluctuations in the electron density. The density oscillations are considered to be manifestations of acoustic waves, which were generated from Alfvén waves originating from the photosphere, and the energy fluxes of those acoustic waves were estimated. The relative density-amplitude peaks around 4 – 6and the wave-energy flux decreases beyond ≈ 6, implying that the acoustic waves dissipate to heat the corona. The phase-scintillation spectrum that we obtained cannot be expressed by a single power law. A break is seen around the frequency of 0.5 – 2 Hz beyond ≈ 6, suggesting an excess power other than turbulence at lower frequencies. The enhancement of the relative density amplitude around 6found by the wavelet analysis might explain this excess power. The acoustic wave-energy flux in the fast solar wind tends to exceed that in the slow wind, suggesting that the fast wind is powered by a larger injection of Alfvén-wave energy than the slow wind.
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