Polarization and scattering of a long-duration meteor trail
Polarization and scattering of a long-duration meteor trail
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长时间流星轨迹的偏振和散射
DOI：
10.1029/2010ja015968
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发表时间：
2011
影响因子：
--
通讯作者：
J. Yee
中科院分区：
文献类型：
--
作者：
S. Close;M. Kelley;L. Vertatschitsch;P. Colestock;M. Oppenheim;J. Yee
[1]在过去的二十年里，高功率大孔径雷达一直被用来确定流星体进入地球大气层时在其周围和后面形成的等离子体的特征。这些等离子体，分别称为头部和尾部，以相对频率（峰值头部回波检测率为1001/s）出现，但非常多样化，难以在一般意义上定义。一种特殊类型的等离子体，被称为非镜面尾迹，当流星体准平行于雷达波束行进时，雷达波束准垂直于背景磁场。反射被认为是发生在轨迹变得不稳定后形成的场向不规则性（FAI）。虽然FAI散射属于大多数持续时间短的非镜面反射轨迹，但这些轨迹的一个子集，称为长持续时间轨迹，仍然有待解释。在本文中，我们提出了一个案例研究分析的一个长时间，非镜面跟踪和相关的头部回波检测到的高级研究计划署（ARPA）的远程跟踪和识别雷达（ALTAIR），这是一个HPLA雷达。这些数据是独一无二的，因为它们是高分辨率（单脉冲角度），双频，最重要的是，双极化，这使得前所未有的洞察散射过程从头部和尾部。首先，我们确定母流星体的速度和质量，母流星体是一种重量超过一毫克的粒子，是ALTAIR探测到的最大的流星体之一。其次，我们确定的峰值等离子体密度和极化的头部回波和特征的独特的，但强返回相反的极化，这可能是由于多个散射中心的范围内的门。最后，我们研究的轨迹的极化特性，并讨论了第一个决定性的证据，极化翻转沿着的轨迹条纹，我们认为这对应于尖锐的梯度在边缘的轨迹有关的湍流混合的尘埃等离子体，是拉长沿着磁场。我们研究一个新的想法，即，一些非镜面回波的概念可能对应于一个高施密特数，尘埃等离子体，是发现和以上的陨石云。我们的研究结果表明，如何极化返回可以帮助散射诊断和单极化雷达必须谨慎使用，以确定头部和尾部等离子体密度的一些回报可能会发生在“意外”的通道。
[1] High-power, large-aperture (HPLA) radars have been used over the past two decades to characterize the plasmas formed both around and behind meteoroids as they enter Earth's atmosphere. These plasmas, referred to as heads and trails, respectively, occur with relative frequency (peak head echo detection rate of ∼1/s) but are extremely diverse and have been difficult to define in a general sense. One particular type of plasma, referred to as the nonspecular trail, occurs when the meteoroid travels quasi-parallel to the radar beam with the radar beam lying quasi-perpendicular to the background magnetic field. Reflection is believed to occur from field-aligned irregularities (FAIs) that form after the trail becomes unstable. While FAI scattering pertains to the majority of nonspecular trails that are short in duration, a subset of these trails, referred to as long-duration trails, still remains open to interpretation. In this paper we present a case study analysis of a long-duration, nonspecular trail and its associated head echo detected with the Advanced Research Project Agency (ARPA) Long-Range Tracking and Identification Radar (ALTAIR), which is an HPLA radar. These data are unique in that they are high resolution (with monopulse angles), dual frequency, and, most importantly, dual polarized, which allows for unprecedented insight into the scattering process from both heads and trails. First, we determine the velocity and mass of the parent meteoroid, which is a particle weighing more than a milligram and is one of the largest meteoroids ever detected by ALTAIR. Second, we determine the peak plasma density and polarization of the head echo and characterize the unique, yet strong returns in the opposite polarization, which may be due to multiple scattering centers within the range gate. Finally, we examine the polarization properties of the trail and discuss the first conclusive evidence of polarization flipping along the trail striations, which we believe corresponds to sharp gradients at the edges of the trail related to turbulent mixing of a dusty plasma that is elongating along the magnetic field. We look into a new idea, namely, the notion that some nonspecular echoes might correspond to a high Schmidt number, dusty plasma, as is found in and above noctilucent clouds. Our results show how polarized return can aid in scattering diagnostics and that single polarization radars must be used with caution for determining head and trail plasma densities given that some of the return can occur in the “unexpected” channel.