Investigating the impact of the latitudinal velocity profile on nonlinear gradient drift instability development in the subauroral ionosphere
Investigating the impact of the latitudinal velocity profile on nonlinear gradient drift instability development in the subauroral ionosphere
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研究纬度速度剖面对极光电离层非线性梯度漂移不稳定性发展的影响
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
B. Srinivasan
中科院分区：
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作者：
Lujain Almarhabi;C. Skolar;W. Scales;B. Srinivasan
极光极化流 (SAPS) 是极光电离层中等离子体密度较低且由极向电场驱动的大西向气流的区域。在 SAPS 区域观察到密度不规则；这些不规则性可能会导致相位和幅度波动，从而对无线电信号产生负面影响。之前的工作将梯度漂移不稳定性（GDI）确定为 SAPS 中电离层不规则性的产生机制，并研究了速度剖面对 GDI 发展的影响。理解 GDI 的湍流谱非常重要，因为它们可以深入了解与可能影响无线电传播的湍流演化相关的空间尺度。我们假设通过中性风的背景电场和速度切变的性质对湍流谱的幂律有影响。二维流体模型用于研究具有固定背景密度分布和不同纬度速度分布的 SAPS 中 GDI 的湍流谱。来自超级双极光雷达网络 (SuperDARN) 雷达和全球定位系统 (GPS) 的数据提供了背景电离层条件。中性风向选择为赤道方向，与典型观测结果相符；然而，这可以用来修改电场以考虑 SAPS 区域的新可能性。电场的角度通过背景速度剖面（漂移）和中性风的组合来体现。分析了没有速度剖面和不同中性风向情况下的湍流谱。通过相对于密度梯度平移速度剪切位置来研究速度剪切的影响。给出了数值光谱分析结果并与最近的实验观察结果进行了比较。发现无背景速度（漂移）的 GDI 模拟的谱斜率结果分别为 和 对于归一化密度和扰动电势。发现不同速度剪切位置模拟的谱斜率分别遵循归一化密度和扰动电势（SAPS 区域内）的幂律 和 。
Subauroral polarization streams (SAPS) are regions in the subauroral ionosphere with lower plasma density and large westward flow driven by a poleward electric field. Density irregularities have been observed in the SAPS region; these irregularities can negatively impact radio signals by causing phase and amplitude fluctuations. Previous work identified the gradient drift instability (GDI) as a generation mechanism of such ionospheric irregularities in SAPS and investigated the impact of the velocity profile on the GDI development. The turbulence spectra of the GDI are important to understand as they can provide insight into spatial scales associated with the turbulent evolution that may impact radio propagation. We hypothesize that the background electric field, through the neutral wind, and the nature of the velocity shear have an impact on the power laws from the turbulence spectra. A 2D fluid model is used to investigate the turbulence spectra of GDI in SAPS with a fixed background density profile and different latitudinal velocity profiles. Data from Super Dual Auroral Radar Network (SuperDARN) radar and Global Positioning System (GPS) provide the background ionospheric conditions. The neutral wind direction is chosen to be in the equatorward direction, which is in line with typical observations; however, this can be used to modify the electric field to consider new possibilities in the SAPS region. The angle of the electric field is manifested through the combination of the background velocity profile ( drift) and the neutral wind. The turbulence spectra of cases with no velocity profile and with different neutral wind directions are analyzed. The impact of velocity shear is studied by translating the velocity shear location relative to the density gradient. Numerical spectral analysis results are presented and compared to recent experimental observations. Results of spectral slopes of GDI simulations with no background velocity ( drift) were found to be and for the normalized density and the perturbed electric potential, respectively. Spectral slopes for simulations with different velocity shear locations were found to follow power laws of and for the normalized density and perturbed electric potential (inside SAPS region), respectively.