A LOFAR observation of ionospheric scintillation from two simultaneous travelling ionospheric disturbances
A LOFAR observation of ionospheric scintillation from two simultaneous travelling ionospheric disturbances
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DOI：
10.1051/swsc/2020010
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发表时间：
2020-03-20
影响因子：
3.3
通讯作者：
Zucca, Pietro
中科院分区：
文献类型：
--
作者：
Fallows, Richard A.;Forte, Biagio;Zucca, Pietro
本文介绍了使用低频阵列（LOFAR）的电离层闪烁的第一次观测的结果之一。观测是在2013年8月18日至19日夜间拍摄的强天然射电源仙后座A，在10-80 MHz的观测带宽内接收到的强度动态谱中显示出中等强度的散射效应。从第一个小时的观察延迟多普勒频谱（2-D FFT的动态频谱）显示两个离散的抛物线弧，一个陡峭的曲率和其他浅，这可以用来提供距离的估计，和速度的散射等离子体。对LOFAR“核心”中密集台站阵列接收到的数据进行互相关分析，发现闪烁模式中有两种不同的速度：主速度约为20-40 ms（-1），从西北向东南方向，与陡峭的抛物线弧和F区或更高的散射高度有关，二次速度约为110 ms（-1），方向为东北至西南，与浅弧和D区散射高度有关。当时中纬度地区的地磁活动很低，但在观测开始时，高纬度地区的一个弱亚暴达到了顶峰。对当时全球导航卫星系统和电离层探测仪数据的分析表明，可能是高纬度活动的结果，有一个较大规模的电离层扰动沿西北至东南方向传播，同时，有一个较小规模的电离层扰动沿东北至西南方向传播，这可能与大气重力波活动有关。LOFAR观测显示了来自两个TID的散射，在不同的高度和不同的方向传播。据我们所知，这是第一次报告这种现象。
This paper presents the results from one of the first observations of ionospheric scintillation taken using the Low-Frequency Array (LOFAR). The observation was of the strong natural radio source Cassiopeia A, taken overnight on 18-19 August 2013, and exhibited moderately strong scattering effects in dynamic spectra of intensity received across an observing bandwidth of 10-80 MHz. Delay-Doppler spectra (the 2-D FFT of the dynamic spectrum) from the first hour of observation showed two discrete parabolic arcs, one with a steep curvature and the other shallow, which can be used to provide estimates of the distance to, and velocity of, the scattering plasma. A cross-correlation analysis of data received by the dense array of stations in the LOFAR "core" reveals two different velocities in the scintillation pattern: a primary velocity of similar to 20-40 ms(-1) with a north-west to south-east direction, associated with the steep parabolic arc and a scattering altitude in the F-region or higher, and a secondary velocity of similar to 110 ms(-1) with a north-east to south-west direction, associated with the shallow arc and a scattering altitude in the D-region. Geomagnetic activity was low in the mid-latitudes at the time, but a weak sub-storm at high latitudes reached its peak at the start of the observation. An analysis of Global Navigation Satellite Systems (GNSS) and ionosonde data from the time reveals a larger-scale travelling ionospheric disturbance (TID), possibly the result of the high-latitude activity, travelling in the north-west to south-east direction, and, simultaneously, a smaller-scale TID travelling in a north-east to south-west direction, which could be associated with atmospheric gravity wave activity. The LOFAR observation shows scattering from both TIDs, at different altitudes and propagating in different directions. To the best of our knowledge this is the first time that such a phenomenon has been reported.