A 50-MHz radio Doppler experiment for midlatitude E region coherent backscatter studies: System description and first results
A 50-MHz radio Doppler experiment for midlatitude E region coherent backscatter studies: System description and first results
复制标题
用于中纬度 E 区域相干反向散射研究的 50 MHz 无线电多普勒实验：系统描述和初步结果
DOI：
10.1029/93rs01373
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发表时间：
1993
期刊：
影响因子：
1.6
通讯作者：
K. Schlegel
中科院分区：
文献类型：
--
作者：
C. Haldoupis;K. Schlegel
与赤道和极光电喷流等离子体相反，中纬度E区域场向不规则体对VHF波散射的研究有限，对该现象的物理学也没有很好的理解。在本文中，我们首先提供了一个更新的主题，然后提出了一个新的实验，表示为零星E散射实验（SESCAT），设计用于高时间分辨率相干后向散射测量3米E区域的不规则性从中纬度位置。该技术多年来在极光纬度地区成功使用，能够在固定范围内非常准确地测量回波信号的多普勒频谱。该实验是最先进的双基地连续波多普勒雷达，工作频率为50.52 MHz，发射和接收阵列向北发射到E区峰值处垂直于地球磁场的区域。观测区域由窄波束交叉图案和不规则性的场对准特征确定，固定在约15×40平方公里，位于爱琴海南部30.8°不变磁纬度（L = 1.35）。第一个结果表明，50 MHz的后向散射事件，信噪比高达25分贝，寿命为几分钟到一个多小时，确实存在于中纬度地区，根据以前的实验，这些回波零星E层。除了下午早些时候的情况外，观察到的事件发生在当地午夜前后几个小时的黑暗时间内。后向散射可以是连续的，但在某些情况下，发现准周期行为，周期在2到10分钟之间。与后向散射相关的是对称的窄多普勒频谱，平均速度在±80 m s-1范围内，平均宽度约为30到60 m s-;1。在频谱宽度方面，中纬度E区域的回波不比较低速2型回波中观察到的赤道和极光电射流。最后，非常强的流星引起的后向散射突然发病和短寿命长达3分钟也被检测到。这些回波在开始时具有相对较大的速度，在一个例子中，在320 m s−1处短暂地看到了离子声速分量，这表明Farley-Buneman不稳定性有时也可能在中纬度E区域起作用。
Contrary to equatorial and auroral electrojet plasmas, studies on scattering of VHF waves from midlatitude E region field-aligned irregularities are limited, and the physics of the phenomena is not well understood. In this paper we provide first an update of the subject and then present a new experiment, denoted as Sporadic E Scatter Experiment (SESCAT), designed for high-time resolution coherent backscatter measurements of 3-m E region irregularities from a middle latitude location. The technique, which is used successfully in auroral latitudes for years, is capable of measuring the Doppler spectrum of the echoing signal at a fixed range with great accuracy. The experiment is a state of the art bistatic CW Doppler radar operating at 50.52 MHz with the transmitting and receiving arrays beaming northward to a region perpendicular to the Earth's magnetic field at the E region peak. The viewing area, determined by the narrow beam intersecting patterns and the field-aligned character of the irregularities, is fixed at about 15×40 km2 and located over the southern Aegean at 30.8° invariant magnetic latitude (L = 1.35). First results show that 50-MHz backscatter events, with snrs as large as 25 dB and lifetimes of several minutes to more than an hour, do exist at midlatitudes in accordance with previous experiments which related these echoes to sporadic E layers. The observed events, except for an early afternoon case, occurred during dark hours in the period between a few hours before and after local midnight. The backscatter can be continuous but in some events a quasi-periodic behavior was found with periods between 2 and 10 min. Associated to the backscatter are symmetric narrow Doppler spectra with mean velocities in the ±80 m s−1 range and mean widths about 30 to 60 m sminus;1. In terms of spectrum width, the midlatitude E region echoes do not compare to the low-velocity type 2 echoes observed in the equatorial and auroral electrojets. Finally, very strong meteor-induced backscatter with abrupt onsets and short lifetimes up to 3 min were also detected. These echoes have relatively large velocities at onset and in one case an ion acoustic velocity component was seen briefly at 320 m s−1, suggesting that the Farley-Buneman instability may also be functioning at times in the midlatitude E region.