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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Polar spacecraft based comparisons of intense electric fields and Poynting flux near and within the plasma sheet-tail lobe boundary to UVI images: An energy source for the aurora
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Polar spacecraft based comparisons of intense electric fields and Poynting flux near and within the plasma sheet-tail lobe boundary to UVI images: An energy source for the aurora

机译：基于极性航天器的等离子体薄板尾叶边界附近和之内的强电场和坡印廷通量与UVI图像的比较：极光的能源

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In this paper, we present measurements from two passes of the Polar spacecraft of intense electric and magnetic field structures associated with Alfven waves at and within the outer boundary of the plasma sheet at geocentric distances of 4-6 R-E near local midnight. The electric field variations have maximum values exceeding 100 mV/m and are typically polarized approximately normal to the plasma sheet boundary. The electric field structures investigated vary over timescales (in the spacecraft Frame) ranging from 1 to 30 s. They are associated with strong magnetic field fluctuations with amplitudes of 10-40 nT which lie predominantly in the plane of the plasma sheet and are perpendicular to the local magnetic field. The Poynting flux associated with the perturbation fields measured at these altitudes is about 1-2 ergs cm(-2) s(-1) and is directed along the average magnetic field direction toward the ionosphere. If the measured Poynting flux is mapped to ionospheric altitudes along converging magnetic field lines, the resulting energy flux ranges up to 100 ergs cm(-2) s(-1). These strongly enhanced Poynting fluxes appear to occur in layers which are observed when the spacecraft is magnetically conjugate (to within a 1 degrees mapping accuracy) to intense auroral structures as detected by the Polar UV Imager (UVI). The electron energy flux (averaged over a spatial resolution of 0.5 degrees) deposited in the ionosphere due to auroral electron beams as estimated from the intensity in the UVI Lyman-Birge-Hopfield-long filters is 15-30 ergs cm(-2)s(-1). Thus there is evidence that these electric field structures provide sufficient Poynting flux to power the acceleration of auroral electrons (as well as the energization of upflowing ions and Joule heating of the ionosphere). During some events the phasing and ratio of the transverse electric and magnetic field variations are consistent with earthward propagation of Alfven surface waves with phase velocities of 4000-10000 km/s. During other events the phase shifts between electric and magnetic fields suggest interference between upward and downward propagating Alfven waves. The E/B ratios an about an order of magnitude larger than typical values of c/Sigma(p), where Sigma(p) is the height integrated Pedersen conductivity. The contribution to the total energy flux at these altitudes from Poynting flux associated with Alfven waves is comparable to or larger than the contribution from the particle energy flux and 1-2 orders of magnitude larger than that estimated from the large-scale steady stale convection electric field and field-aligned current system. [References: 45]
机译：在本文中，我们介绍了来自极地飞船两次通过的强电场和磁场结构的测量结果，这些结构与在局部午夜附近的地心距为4-6 R-E的等离子薄片外边界处和内部的Alfven波有关。电场变化的最大值超过100 mV / m，通常被极化成近似垂直于等离子片边界。所研究的电场结构在1到30 s的时间范围内（在航天器框架中）变化。它们与振幅为10-40 nT的强磁场波动有关，该波动主要位于等离子片的平面内，并且垂直于局部磁场。与在这些高度上测得的扰动场相关的珀因廷通量约为1-2 ergs cm（-2）s（-1），并沿着平均磁场方向指向电离层。如果将测量的坡印廷通量沿着会聚的磁力线映射到电离层高度，则产生的能量通量范围可达100 ergs cm（-2）s（-1）。这些强烈增强的珀因廷通量似乎出现在层中，这些层是在航天器通过极紫外成像仪（UVI）检测到与强极光结构磁性共轭（映射精度在1度以内）时观察到的。根据UVI Lyman-Birge-Hopfield-long滤光片的强度估算，由于极光电子束，电离层中沉积在电离层中的电子能量通量（在0.5度的空间平均值上平均）为15-30 ergs cm（-2）s （-1）。因此，有证据表明，这些电场结构提供了足够的Poynting通量来驱动极光电子的加速（以及向上流动的离子的激发和电离层的焦耳热）。在某些事件中，横向电场和磁场变化的相位和比率与相速度为4000-10000 km / s的Alfven表面波向地球传播一致。在其他事件中，电场和磁场之间的相移表明向上和向下传播的Alfven波之间存在干扰。 E / B比大约比c / Sigma（p）的典型值大一个数量级，其中Sigma（p）是高度积分的Pedersen电导率。与Alfven波有关的珀因廷通量在这些高度上对总能量通量的贡献与粒子能通量的贡献相当或更大，并且比大型稳态陈旧对流电估算的能量要大1-2个数量级。场和场对齐的当前系统。 [参考：45]

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