AI 中文总结
研究行星际日冕物质抛射中尺度波动的光谱特性，用小波功率谱分析142个ICME区间，发现中尺度光谱斜率更平缓，波动有高交叉螺旋度、低压缩性等特点，慢风区间类似，表明ICMEs中尺度存在光谱狭窄的\(1/f\)范围。
AI 中文摘要
行星际日冕物质抛射（ICMEs）中的磁场通常在大尺度上呈现通量绳结构，在较小尺度上呈现波动的湍流级联。然而，通量绳和湍流之间过渡尺度（即中尺度）的波动性质此前尚未得到详细研究。本文使用小波功率谱研究了142个在1天文单位处具有清晰通量绳特征的ICME区间内磁场的中尺度波动，“中尺度”定义为航天器坐标系频率\(10^{-4}\ \text{Hz}<f_\mathrm{sc}< 10^{-3}\ \text{Hz}\)，相当于时间尺度\(2.8\ \text{hr}\gtrsim \tau \gtrsim 17\ \text{min}\)。发现中尺度光谱比大尺度和小尺度光谱的斜率明显更平缓，这些中间尺度的平均光谱斜率接近\(-1\)。中尺度波动具有较高的交叉螺旋度幅值和低压缩性，表明具有显著程度的阿尔文性，同时其负剩余能量比小尺度湍流波动更多。利用中尺度光谱斜率值的不确定性区分呈现相对平滑幂律行为或（较少见）更崎岖趋势的光谱；较平滑的幂律区间具有平衡的交叉螺旋度分布，而更崎岖的光谱主要具有背日向交叉螺旋度。对慢风区间进行了类似分析，结果与ICMEs相似。这些结果表明，ICMEs在中尺度上通常存在一个光谱狭窄的\(1/f\)范围。
英文摘要
Magnetic fields in interplanetary coronal mass ejections (ICMEs) often display a flux rope structure at large scales and a turbulent cascade of fluctuations at smaller scales. However, the nature of fluctuations at transition scales between the flux rope and turbulence - i.e., at mesoscales - has not been previously examined in detail. Mesoscale fluctuations of the magnetic field in 142 ICME intervals with clear flux rope signatures at 1 au have been examined using wavelet power spectra, with "mesoscale" defined here as spacecraft-frame frequencies $10^{-4}\ \text{Hz}<f_\mathrm{sc}< 10^{-3}\ \text{Hz}$, equivalent to timescales $2.8\ \text{hr}\gtrsim τ\gtrsim 17\ \text{min}$. The spectra were found to be significantly less steep at mesoscales than at larger and smaller scales, with an average spectral slope close to $-1$ at these intermediate scales. The mesoscale fluctuations had relatively high cross helicity magnitudes and low compressibility, suggesting a significant degree of Alfvénicity, while also having more negative residual energy than the turbulent fluctuations found at smaller scales. Uncertainties in the spectral slope values at mesoscales were used to distinguish between spectra showing a relatively smooth power-law behavior or (less commonly) a more bumpy trend; the smoother power-law intervals had a balanced cross helicity distribution while the more bumpy spectra had a predominantly antisunward cross helicity. Slow wind intervals were similarly analyzed, and showed similar properties to the ICMEs. These results indicate that a spectrally narrow $1/f$ range is typically present in ICMEs at mesoscales.
Comments9 pages, 8 figures
