The effect of gravity and pressure in the electrodynamics of the low‐latitude ionosphere
The effect of gravity and pressure in the electrodynamics of the low‐latitude ionosphere
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重力和压力对低纬度电离层电动力学的影响
DOI：
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发表时间：
2004
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通讯作者：
J. Eccles
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文献类型：
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作者：
J. Eccles
[1] 磁静期间低纬度电离层中等离子体漂移结构的来源已大致了解。几乎所有静时电场结构都归因于中性风电流发电机的散度。然而，在低纬度电离层中还有其他活跃的电流驱动因素：重力驱动电流（O⁺的g×B漂移）和梯度 - 压力电流（电子和O⁺的∇P×B漂移）。重力驱动电流在瑞利 - 泰勒不稳定性和赤道扩展F（ESF）的发展中很重要，但在全球发电机电场模型中被忽略。电离层动量方程中的梯度压力项和重力项通常相互抵消。本文在一个耦合的电离层 - 电动力学模型中研究了由这些较小电流的散度所产生的大尺度电场的大小。中性风发电机产生的低纬度电场仅被这些附加项略微改变。由此产生的垂直电场（纬向等离子体漂移）没有显著变化，但在日出前和日落后的几个小时内，垂直等离子体漂移受到约10到15米/秒的影响。这些低纬度等离子体漂移差异完全是由于包含了重力驱动电流。重力电流项在日落后产生向下漂移，这减弱了傍晚的预反转增强。此外，日出前的正垂直漂移有时足够大，会导致黎明前的垂直增强。对于大尺度和中尺度的电离层特征，梯度压力项可以忽略。
[1] The source of the plasma drift structure in the low-latitude ionosphere during magnetically quiet times is generally understood. Nearly all the quiet time electric field structure has been attributed to divergences in the neutral wind current dynamo. However, there are other current drivers active in the low latitude ionosphere: a gravity-driven current (g × B drift of O+) and a gradient-pressure current (∇P × B drift of e and O+). The gravity-driven current is important in the development of the Rayleigh-Taylor instability and equatorial spread F (ESF) but is ignored in global dynamo electric field models. The gradient pressure and gravity terms in the ionosphere momentum equation normally oppose each other. This paper examines the magnitude of the large-scale electric fields generated by divergences in these lesser currents in a coupled ionosphere-electrodynamics model. The low-latitude electric fields generated by the neutral wind dynamo are altered only slightly by these additional terms. The resulting vertical electric fields (zonal plasma drifts) do not change significantly but the vertical plasma drifts are affected by ∼10 to 15 m/s in the hours before sunrise and after sunset. These low-latitude plasma drift differences are due entirely to the inclusion of the gravity-driven current. The gravity current term produces a downward drift after sunset, which reduces the evening prereversal enhancement. Additionally, the positive vertical drift before sunrise is sometimes large enough to cause a predawn vertical enhancement. The gradient pressure terms can be ignored for large and medium scale ionosphere features.