Characteristics and implications of Doppler spectra of E region quasi-periodic echoes observed by the multibeam middle and upper atmosphere radar
Characteristics and implications of Doppler spectra of E region quasi-periodic echoes observed by the multibeam middle and upper atmosphere radar
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DOI：
10.1029/2005ja011335
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发表时间：
2006-05
影响因子：
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通讯作者：
T. Ogawa;Y. Otsuka;M. Yamamoto
中科院分区：
文献类型：
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作者：
T. Ogawa;Y. Otsuka;M. Yamamoto
我们给出了来自日本滋贺县3.2米场向不规则体的准周期（QP）回波的多波束中高层大气（MU）雷达观测结果，这些不规则体与夜间中纬度散在E层（Es）中的等离子体斑有关，以给出QP回波特征的一个连贯视图。纬向尺度小于50千米的回波区域在约105千米高度向西移动，迹线速度为110 - 120米/秒，并相继穿过雷达波束。回波的多普勒频谱在时间、距离和方位上发生变化，主要呈现出多普勒速度在 - 200到 + 200米/秒之间的2型回波，偶尔由于双流不稳定性出现1型回波（“MU雷达首次探测到1型回波”）。我们发现漂移回波区域中部附近的频谱有两个2型峰，一个在正多普勒速度（远离雷达的运动）处，另一个在负多普勒速度（朝向雷达的运动）处，并且回波区域西部和东部的频谱分别在正和负多普勒速度处有单个2型峰。有趣的是，在固定波束上持续约4分钟的1型回波位于回波区域的中部附近。它们在250到320米/秒之间的多普勒频移与之前在其他中纬度地区的1型回波观测结果非常一致。偶尔，1型和2型回波在相同的距离门中同时存在。基于近期与QP回波相关的观测、理论和模拟，我们提出了一个Es等离子体斑的简单模型来解释这些观测结果。在该模型中，沿西北 - 东南方向拉长的、在斑内部和外部极性相反的极化电场在激发1型和2型回波方面起主要作用，并导致多种多普勒频谱。
[i] We present multibeam middle and upper atmosphere (MU) radar observations of quasi-periodic (QP) echoes from 3.2-m field-aligned irregularities associated with plasma patches in the nighttime midlatitude sporadic E (E s ) layers over Shigaraki, Japan, to give a cohesive view of the QP echo characteristics. Echo regions with zonal scales less than 50 km moved westward at altitudes near 105 km with trace velocities of 110-120 m s -1 and crossed the radar beams successively. Doppler spectra of the echoes changed in time, range, and azimuth and exhibited mostly type 2 echoes with Doppler velocities between -200 and +200 m s -1 and occasionally type 1 echoes due to the two-stream instability ("the first type 1 echo detection by the MU radar"). We find that the spectra near the middle of the drifting echo region have two type 2 peaks, one at positive Doppler velocity (motion away from the radar) and the other at negative one (motion toward the radar) and that the spectra in the west and east parts of the echo region have single type 2 peak at positive and negative Doppler velocities, respectively. Interestingly, the type 1 echoes lasting for about 4 min on a fixed beam were located near the middle of the echo region. Their Doppler shifts between 250 and 320 m s -1 are very consistent with those from previous type 1 echo observations at other midlatitude locations. Occasionally, type 1 and type 2 echoes coexisted in the same range gates. On the basis of recent observations, theories, and simulations related to QP echoes, we propose a simple model of an E s plasma patch to explain the observations. In the model, polarization electric fields with opposite polarity inside and outside the patch, elongated along the NW-SE direction, play a predominant role in exciting type 1 and type 2 echoes, and cause a variety of Doppler spectra.