基于三亚VHF雷达的场向不规则体观测研究:2.东亚低纬电离层E区准周期回波

中低纬电离层E区不规则体准周期雷达回波现象,在地球不同经度区被观测到并开展了有关研究.本文利用三亚(109.6°E,18.4°N)VHF相干散射雷达2011年2月6日的观测,第一次给出了中国低纬电离层E区准周期回波的发生和变化特征.观测结果表明:准周期回波发生在地方时夜间2100—2200LT的110km高度上,与连续性回波可同时发生;准周期回波斜纹在雷达探测的高度-时间-强度(HTI)图上可延伸5～20km,持续时间为5～15min,回波斜纹高度随时间以20～30m/s下降,斜纹在HTI图上彼此间隔10km和10min左右.此外,雷达回波多普勒谱和雷达干涉分析显示不同高度准周期回波的多普勒速度随高度-时间表现出不同的变化趋势,与回波条纹斜率无明显联系,不同高度准周期回波对应的不规则体在东西方向也表现出截然不同的运动特征.分析结果表明,三亚电离层E区准周期回波的发生可能并不是由散块Es随着中性风周期性的经过雷达探测区域所致,而可能和Es中的扰动结构相关.     

基于三亚VHF雷达的场向不规则体观测研究:4.太阳活动低年夏季F区回波

太阳活动低年夏季,低纬电离层F区场向不规则体表现出与太阳活动高年和其他季节明显不同的特征.本文利用我国三亚站(18.4°N,109.6°E,地磁倾角纬度dip latitude 12.8°N)VHF雷达、电离层测高仪、GPS闪烁监测仪和美国C/NOFS卫星观测数据,研究了太阳活动低年夏季我国低纬电离层F区场向不规则体的基本特征.分析发现无论磁静日还是磁扰日,夏季电离层F区不规则体回波主要出现于地方时午夜以后,回波出现的时间较短,高度范围较小,伴随着扩展F出现,但没有同时段的L波段电离层闪烁.太阳活动低年夏季午夜后的低纬电离层F区不规则体回波,可能并不总是与赤道等离子体泡沿磁力线向低纬地区的延伸相关,而可能由本地Es等扰动过程引起.     

基于三亚VHF雷达的场向不规则体观测研究：4.太阳活动低年夏季F区回波

太阳活动低年夏季,低纬电离层F区场向不规则体表现出与太阳活动高年和其他季节明显不同的特征.本文利用我国三亚站（18.4°N,109.6°E,地磁倾角纬度dip latitude 12.8°N）VHF雷达、电离层测高仪、GPS闪烁监测仪和美国C/NOFS卫星观测数据,研究了太阳活动低年夏季我国低纬电离层F区场向不规则体的基本特征.分析发现无论磁静日还是磁扰日,夏季电离层F区不规则体回波主要出现于地方时午夜以后,回波出现的时间较短,高度范围较小,伴随着扩展F出现,但没有同时段的L波段电离层闪烁.太阳活动低年夏季午夜后的低纬电离层F区不规则体回波,可能并不总是与赤道等离子体泡沿磁力线向低纬地区的延伸相关,而可能由本地Es等扰动过程引起.     

暴时低纬电离层不规则体响应特征的多手段观测

2010年10月11日发生了一次中等强度的磁暴.本文利用三亚(18.4°N,109.6°E)数字测高仪、VHF雷达和GPS TEC/闪烁监测仪数据以及120°E子午线附近我国漠河(53.5°N,122.4°E)、北京(40.3°N,116.2°E)和武汉(30.6°N,114.4°E)的数字测高仪和GPS TEC/闪烁监测仪数据,分析了磁暴期间我国中低纬地区电离层不规则体的响应特征.结果表明:这次磁暴触发了10月11日午夜前后两个时段低纬(三亚)电离层不规则体事件,而在较高的纬度地区(武汉及以北),并没有观测到电离层不规则体与闪烁.在午夜前,电离层不规则体的发生受磁暴主相期间快速穿透电场激发;在午夜后,电离层不规则体受磁暴恢复相的扰动发电机电场触发,该时段伴随行星际磁场北向翻转的过屏蔽穿透电场也可能是扰动源之一.此外,磁暴期间不同尺度的电离层不规则体会伴随发生.     

电离层不规则结构漂移的GPS测量及其初步结果

本文阐述了利用GPS接收机台阵测量到的闪烁和TEC变化率ROT快速起伏图样估计F层不规则结构漂移的原理和方法,并利用实测数据估计了静日和暴时电离层不规则结构的水平漂移速度.短间距台网和超短间距台链观测实例的计算结果表明,暴时武汉地区引起TEC快速起伏的电离层不规则结构沿纬圈向西漂移,21∶30至03∶00 LT,西向漂移速度在约40 m/s至130 m/s的范围内变化;在桂林地区,磁静日午夜前后引起L波段电波闪烁的电离层不规则结构沿纬圈向东漂移,漂移速度从约70 m/s下降到约55 m/s,磁扰日午夜前不规则结构向西漂移,速度从约150 m/s下降到约50 m/s,午夜后转为向东漂移,速度从约25 m/s上升到约65 m/s.文中还提出了由单站多卫星观测估计F层不规则结构漂移的设想.实例分析与计算结果表明,利用单站多卫星观测估计电离层不规则结构漂移是一种合理可行的方法.     

不同尺度低纬电离层不规则体漂移特性的观测研究

利用我国三亚站GPS短基线接收机阵以及VHF电离层相干散射雷达多波束扫描模式进行同时观测,对2011年10月22日至29日夜间两种不同尺度电离层不规则体的纬圈漂移速度进行比较研究.结果表明,两种不同手段观测的不同尺度不规则体漂移速度,在大小、变化趋势以及时间范围上基本一致.不规则体产生在20:00 LT(LT为北京时)左右,以100～250 m/s的速度东向漂移,并且速度幅值起伏较大;在不规则体发展中后期(21:00LT以后),东向漂移速度减低到50～150m/s,并延续至午夜.两种手段观测的漂移速度差异,一个重要原因可能来自于两者观测范围的不同.此外,GPS短基线接收机阵观测的400米尺度电离层不规则体通常比VHF雷达探测到的3米尺度电离层不规则体存在的时间要长.     

汶川地震同震电离层扰动研究

利用中国大陆陆态观测网(CMONOC)的下关、 昆明和庐州GPS台站, 对汶川地震引起的同震电离层扰动(CID)进行研究。 通过对GPS原始观测数据进行处理证实汶川地震存在5个明显的同震电离层扰动(CID)现象。 根据GPS TEC时间序列和走时, 得到在电离层高度CID的水平传播速度为1.1 km/s, 属于震中区地表抬升引起的声波在电离层中传播速度; 同时, 也得到次一级CID传播速度接近0.7 km/s, 认为可能是重力波。 在此基础上, 利用射线追踪模型寻找震中位置发现, 当CID水平传播速度为1000 m/s时, 发震时刻对应的标准偏差能达到最小值19.55 s, 相应的CID起源位置是30.8°N, 103.15°E, 距离实际震中西南方向33.6 km。     

利用COSMIC掩星探测分析120°E经线附近电离层E层闪烁指数变化

利用气象、电离层和气候卫.星联合观测系统COSMIC掩星2007-2013年探测资料,分析了120°E经线附近电离层E层区域(70~140km)闪烁指数的季节、地方时和空间变化.结果表明强电离层闪烁主要集中在磁纬度±30°内,夏季达到最大,冬季其次,春季最小.闪烁峰值大小与太阳辐射有关,但北半球夏冬季闪烁峰值大于南半球观测结果,秋半球闪烁峰值大于春半球观测结果.地磁高纬地区较强闪烁现象出现在地方时傍晚之后,午夜前后达到最大值.地磁中纬和低纬区域日出后即出现较为明显的闪烁现象,一直持续至夜间甚至凌晨,分别约在中午和傍晚前达到最大值.磁赤道区闪烁现象通常始于地方时日出后,最大值发生在傍晚1800LT左右.电离层E区的闪烁峰值大都集中110km高度,但高纬地区的峰值高度略有降低.此外,太阳和地磁活动的增强一定程度上会抑制E层闪烁现象.相关研究结果有利于分析E层不规则结构及物理形成机制,同时为电离层区域闪烁模型的建立提供有用的信息.     

基于中国中东部多站流星雷达的二维风场观测研究

全天空流星雷达广泛应用于中间层-低热层大气水平风场的观测,为研究该区域大气风场的变化特征提供了重要数据支持.目前流星雷达主要采用单站观测模式,没有水平分辨率,并且只能探测流星区域的大气平均水平风场.为了得到更加丰富且精准的中间层-低热层大气风场信息,本研究介绍了建设在中国安徽地区的多站流星雷达系统,该系统包括安装在蒙城（33.36°N, 116.49°E）的一台单站流星雷达和长丰（31.98°N, 117.22°E）的一台远程接收机,两地直线距离约为167km.相比于单站流星雷达,多站流星雷达系统探测到的前向散射流星数目增加了约70%,并且一般可以提供400 km×400km以上的水平观测区域.除此之外,多站流星雷达系统还可以提供更加丰富的流星观测角度.新多站系统可以实现中间层-低热层大气二维水平风场的观测,在获取平均水平风场以及风场水平梯度的同时,还可以估计水平风场的散度、相对涡度和拉伸、剪切形变信息.多站流星雷达能够提供更多的水平风场参数,对进一步研究中间层-低热层区域的大气动力学过程具有重要意义.不仅如此,未来即将建成的多站流星雷达观测网将会实现中国中东部地区上空的中间层-低热层...     

2011年5月26日北京上空TeSL与Es、大气风场的同时观测

本文报道了北京延庆（116.0°E,40.5°N）钠荧光激光雷达在2011年5月26日夜间观测到的一例低热层钠层（lower thermospheric-enhanced sodium layer,TeSL）事例,从数据采集开始到观测结束,该低热层钠层持续存在且不断增强,峰值密度从250 cm^-3增加至1500 cm^-3,峰值高度却从111 km逐渐下降到100 km.同一时间相距28 km的测高仪也观测到了出现在106~117 km的Es层,平均强度4.5 MHz;对流星雷达设备观测到的75~100 km的纬向风风速进行拟合,得到100~125 km的风速,风剪切节点从122 km下降到108 km.Es层和纬向风剪切节点的演化趋势与TeSL事件呈现出极好的相关性.我们计算了离子垂直速度及辐射复合反应的生成率,对钠原子的出现高度和密度做出解释,推测风剪切汇聚的Na⁺与Es层中的电子中和,是形成当日TeSL的主要机制.     

Observations of 50-MHz type-II coherent echoes from within the polar cap

50-MHz type-II coherent echoes at geometrical aspect angles of 11.5○ have been observed in the northern polar cap during pre-noon hours. The echoes had an unusually large Doppler width of 1200–1400 m s⁻¹ and were well correlated with strong magnetic disturbances in the range 500–1000 nT. The dependence of intensity, spectral width and skewness versus radial velocity were similar to those known from previous experiments at lower latitudes and at small aspect angles. It is concluded that echo onset was due to the combination of several factors, including a highly conducting ionosphere, the presence of a very intense electric field, and strong radar wave refraction.     

Non-magnetic aspect sensitive auroral echoes from the lower E region observed at 50 MHz

Backscatter from E-region irregularities was observed at aspect angles close to 90° (almost parallel to the direction of the magnetic field) using the ALOMAR SOUSY radar at Andoya/Norway. Strong electric fields and increased E-region electron temperatures simultaneously measured with the incoherent scatter facility EISCAT proved that the Farley-Buneman plasma instability was excited. In addition, strong particle precipitation was present as inferred from EISCAT electron densities indicating that the gradient drift instability may have been active, too. Backscatter at such large aspect angles was not expected and has not been observed before. The characteristics of the observed echoes, however, are in many aspects completely different from usual auroral radar results: the Doppler velocities are only of the order of 10 m/s, the half-width of the spectra is around 5 m/s, the echoes originate at altitudes well below 100 km, and they seem to be not aspect-sensitive with respect to the magnetic field direction. We, therefore, conclude that the corresponding irregularities are not caused by the mentioned instabilities and that other mechanism have to be invoked.     

基于三亚VHF雷达的场向不规则体观测研究：3. 距离扩展流星尾迹回波

距离扩展流星尾迹回波 （RSTE,range spread trail echo）观测通常采用高功率大孔径雷达.本文利用三亚 （18.4°N,109.6°E） VHF雷达观测,分析研究了小功率VHF雷达观测的RSTE特征.结果表明,三亚VHF雷达在相干散射模式观测的RSTE,其发生和演化的主要形态特征类似高功率大孔径雷达的观测结果.通过2011年8月期间,三亚VHF雷达相干散射模式观测的RSTE,与同时的全天空流星模式观测的镜面流星尾迹（SE,specular trail echo）数据,统计分析了RSTE和SE随地方时以及高度的变化,发现短持续时间RSTE（小于等于15 s）与SE具有类似的时间-高度变化特征,而长持续时间RSTE（大于等于15 s）发生的峰值时间,相比SE和短持续时间RSTE向晨侧偏移,且长持续时间RSTE对高度的依赖性比短持续时间RSTE显著.此外,全天空流星模式观测SE 的数量远多于相干散射模式观测的RSTE数量,可能与不同模式下的观测角度、波束宽度等因素相关.     

Characteristics of very large aspect angle E-region coherent echoes at 933 MHz

The EISCAT UHF radar system was used to study the characteristics of E-region coherent backscatter at very large magnetic aspect angles (5–11°). Data taken using 60 s pulses during elevation scans through horizontally uniform backscatter permitted the use of inversion techniques to determine height profiles of the scattering layer. The layer was always singly peaked, with a mean height of 104 km, and mean thickness (full width at half maximum) of 10 km, both independent of aspect angle. Aspect sensitivities were also estimated, with the Sodankylä-Tromsø link observing 5 dB/degree at aspect angles near 5°, decreasing to 3 dB/degree at 10° aspect angle. Observed coherent phase velocities from all three stations were found to be roughly consistent with LOS measurements of a common E-region phase velocity vector. The E-region phase velocity had the same orientation as the F-region ion drift velocity, but was approximately 50% smaller in magnitude. Spectra were narrow with skewness of about –1 (for negative velocities), increasing slightly with aspect angle.     

On the collocation between dayside auroral activity and coherent HF radar backscatter

The 2D morphology of coherent HF radar and optical cusp aurora has been studied for conditions of predominantly southward IMF conditions, which favours low-latitude boundary layer reconnection. Despite the variability in shape of radar cusp Doppler spectra, the spectral width criterion of 220 m s^–1 proves to be a robust cusp discriminator. For extended periods of well-developed radar backscatter echoes, the equatorward boundary of the 220 m s^–1 spectral width enhancement lines up remarkably well with the equatorward boundary of the optical cusp aurora. The spectral width boundary is however poorly determined during development and fading of radar cusp backscatter. Closer inspection of radar Doppler profile characteristics suggests that a combination of spectral width and shape may advance boundary layer identification by HF radar. For the two December days studied the onset of radar cusp backscatter occurred within pre-existing 630.0 nm cusp auroral activity and appear to be initiated by sunrise, i.e. favourable radio wave propagation conditions had to develop. Better methods are put forward for analysing optical data, and for physical interpretation of HF radar data, and for combining these data, as applied to detection, tracking, and better understanding of dayside aurora. The broader motivation of this work is to develop wider use by the scientific community, of results of these techniques, to accelerate understanding of dynamic high-latitude boundary-processes. The contributions in this work are: (1) improved techniques of analysis of observational data, yielding meaningfully enhanced accuracy for deduced cusp locations; (2) a correspondingly more pronounced validation of correlation of boundary locations derived from the observational data set; and (3) a firmer physical rationale as to why the good correlation observed should theoretically be expected.     

昆明全天空流星雷达观测中高层大气温度

利用昆明电波观测站（25.6°N,103.8°E）两台不同工作频率的全天空流星雷达在2011年特殊联合观测试验期间的数据,基于Hocking的方法利用不同的温度梯度,在确定了昆明地区中层顶位于流星峰值高度之上的情况下,反演了昆明地区上空88 km和85 km高度的大气温度,并与Aura卫星观测的温度进行比较.对比研究发现,两台流星雷达可以分别正确获得88 km和85 km高度的大气温度,但其中由全球温度梯度模式反演得到的大气温度与卫星观测温度相关性不是很好,而利用卫星观测的温度梯度,两台雷达反演出的大气温度与卫星观测温度存在很好的相关性.结果表明了准确的温度梯度在流星雷达观测大气温度过程中是至关重要的.     

Ozone concentration at meteor heights determined from forward-scatter radar echoes

The ozone concentration has been measured in the meteor zone using a method of radar echo duration distribution suggested by Jones and Šimek (1995). Data obtained by the forward-scatter system during the Lyrid meteor shower period in five consecutive years 1992–1996 agree with the Solar Mesosphere Explorer results for the same heights of 95 km. The mean value of the ozone concentration [O₃]=(1.56±0.05)×10¹⁴ m⁻³ has been derived from a total of 6596 radar meteor echoes with duration ≥1 s. The results for individual years indicating a possible decrease in [O₃] are discussed.     

中山站高频雷达回波的日变化特征及地磁活动的影响

利用新建中山站高频雷达2010年4月到2011年2月的观测数据,研究了中山站高频雷达回波的日变化特征以及地磁活动的影响. 研究结果表明,中山站高频雷达回波具有明显的日变化特征且受地磁活动影响较大. 雷达回波发生率的峰值在地磁活动较小时处于日侧;随着地磁活动的增强,峰值减小并向夜侧移动. 另外,平均多普勒视线速度具有明显的昼夜分布,夜侧主要为正向速度,即朝向雷达,日侧主要为负向速度,即远离雷达;随着地磁活动的增强,平均回波强度和平均多普勒视线速度的峰值都会增加,而多普勒谱宽则会减小.     

Midlatitude type 1 echoes observed with the Chung-Li 52 MHz radar

This paper presents observational characteristics of midlatitude ionospheric E region type 1 echoes measured with a 52 MHz Doppler radar located at the National Central University, Chung-Li, Taiwan. Two events, on August 13 and October 15, 1997, are considered which show clear evidence of type 1 echo occurrence with peak Doppler velocities at about −300 m/s and +270 m/s, respectively. On the other hand, interferometry measurements indicate that the drift motion of the scattering region is eastward in both events, at about 80–100 m/s.