Gradient Winds and Neutral Flow Dawn‐Dusk Asymmetry in the Auroral Oval During Geomagnetically Disturbed Conditions
Gradient Winds and Neutral Flow Dawn‐Dusk Asymmetry in the Auroral Oval During Geomagnetically Disturbed Conditions
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DOI：
10.1029/2021ja029936
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发表时间：
2021-12
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影响因子：
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通讯作者：
M. Larsen;R. Pfaff;R. Mesquita;S. Kaeppler
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文献类型：
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作者：
M. Larsen;R. Pfaff;R. Mesquita;S. Kaeppler
洛仑兹力的佩德森分量产生一个加速度，通常在极光椭圆的黎明和黄昏部分的大部分区域内沿纬向方向。在地磁扰动的条件下，随着中性流开始通过离子拖曳力加速，流速增加，科里奥利力、曲率和压力梯度力之间在赤道方向上形成平衡，这些力在低热层中占主导地位。描述这种平衡的梯度风方程预测，黎明侧的气旋流仅限于所谓的规则解，其最大值为地转风速的两倍。另一方面，黄昏一侧的反气旋流可以满足规则解或异常解，其过渡速度为地转风速的两倍。异常流解的风速明显大于过渡值，但受到惯性风值的限制，即对应于曲率和科里奥利力之间平衡的值。进行分析以显示这一结果，这表明黎明侧和黄昏侧气流之间预期存在显著的定量不对称性，正如观测和一些数值模拟研究所观察到的那样。扰动压力梯度和惯性不稳定的风分布的影响进行了讨论。
The Pedersen component of the Lorentz force produces an acceleration that is generally in the zonal direction in much of the dawn and dusk sectors in the auroral oval. During geomagnetically disturbed conditions, as the neutral flow begins to accelerate through the ion drag force and the flow speeds increase, a balance develops in the meridional direction between the Coriolis, curvature, and pressure gradient forces, which are dominant in the lower thermosphere. The gradient wind equation that describes this balance predicts that the cyclonic flow on the dawn side is limited to the so‐called regular solution, which has a maximum value of twice the geostrophic wind speed. The anticyclonic flow on the dusk side, on the other hand, can satisfy either the regular or anomalous solution with a transition at twice the geostrophic wind speed. The anomalous flow solutions have wind speeds significantly greater than the transition value, but are limited by the inertial wind value, that is, the value that corresponds to a balance between the curvature and Coriolis forces. The analysis is carried out to show this result, which indicates that a significant quantitative asymmetry is expected between the dawn‐ and dusk‐side flow, as is observed and has been shown in both observations and a number of numerical modeling studies. Implications for the wind distribution of perturbed pressure gradients and inertial instability are discussed.