Comparison of the reaction of polar mesosphere winter echoes and polar mesosphere summer echoes to high-frequency heating in terms of modulated characteristics

In this work,for the first time,we have analyzed and compared the responses of polar mesosphere winter echoes(PMWE)and their summer counterpart,polar mesosphere summer echoes(PMSE),to high-frequency(HF)heating in terms of modulated characteristics(i.e.,backscatter intensity reduction,recovery,and overshoot).Both PMWE and PMSE observations were from the same site(Tromsφ,Norway;69.6°N,19.2°E)and radar(EISCAT[European Incoherent Scatter Scientific Association]very high frequency,224 MHz).The heating patterns of both PMWE and PMSE were found to be similar;however,PMSE was more greatly affected by HF heating.Polar mesosphere summer echoes showed recovery and overshoot more frequently than did PMWE.In addition,the mean recovery and overshoot of PMSE were greater than those of PMWE.The associated electron temperature enhancement was estimated for both PMWE and PMSE and showed that,compared with PMWE,the electron temperature enhancement was more significant in PMSE.The strong heating effects on PMSE may be due to the considerable increase in electron temperature.

On the radar frequency dependence of polar mesosphere summer echoes

Polar mesosphere summer echoes(PMSEs)are very strong radar echoes in the polar mesopause in local summer.Here we present the frequency dependence of the volume reflectivity and the effect of energetic particle precipitation on modulated PMSEs by using PMSEs observations carried out by European Incoherent SCATter(EISCAT)heating equipment simultaneously with very high frequency(VHF)radar and ultra high frequency(UHF)radar on 12 July 2007.According to the experimental observations,the PMSEs occurrence rate at VHF was much higher than that at UHF,and the altitude of the PMSEs maximum observed at VHF was higher than that at UHF.Overlapping regions were observed by VHF radar between high energetic particle precipitation and the PMSEs.In addition,highfrequency heating had a very limited impact on PMSEs when the UHF electron density was enhanced because of energetic particle precipitation.In addition,an updated qualitative method was used to study the relationship between volume reflectivity and frequency.The volume reflectivity was found to be inversely proportional to the fourth power of radar frequency.The theoretical and experimental results provide a definitive data foundation for further analysis and investigation of the physical mechanism of PMSEs.

Reflection Characteristics of Layered Media in Polar Mesopause Related to Polar Mesosphere Summer Echoes

Polar mesosphere summer echoes （PMSE） are very strong radar echoes from alti- tudes close to the polar summer mesopause. The data from sounding rocket campaigns indicate that the radar signal to noise ratio （SNR）, electron density and dust charge density of polar meso- sphere in summer show obvious layered structure. In this paper the theory of wave propagation in layered media is used to study the reflectance and SNR at each layer in polar mesosphere. The calculated SNR using theory of dusty plasma is found in good agreement with the experimental result, which may imply that the intensity of the radar echoes reflected by the layered structure in polar mesosphere where polar mesosphere summer echoes used to occur can interpret partially the phenomenon of PMSE. In other words, reflection may play an important role in the occurrence of PMSE.

Preliminary Study on Active Modulation of Polar Mesosphere Summer Echoes with the Radio Propagation in Layered Space Dusty Plasma

Radar echoes intensity of polar mesosphere summer echoes（PMSE） is greatly affected by the temperature of dusty plasma and the frequency of electromagnetic wave about the radar.In this paper,a new method is developed to explain the active experiment results of PMSE.The theory of wave propagation in a layered media is used to study the propagation characteristics of an electromagnetic wave at different electron temperatures.The simulation results show that the variation tendency of the reflected power fraction almost agrees with the results observed by radar in the European Incoherent Scatter Scientific Association（EISCAT）.The radar echoes intensity of PMSE greatly decreases with the increase of the radio frequency and the enhancement of the electron temperature.

Study on the Relation Between the Reflectivity and Frequency in Dusty Plasma of the Polar Summer Mesopause

Relation between the volume reflectivity and frequency in view of the polar mesosphere summer echoes （PMSE） is studied using the small-scale structure of electron density caused by charged dust particles. A theoretical expression for the radar volume reflectivity is derived, which agrees with the statistical result. Both the theoretical and statistical results are confirmed with the data obtained from simultaneous observations at three frequencies. Hence the small-scale structure caused by charged dust particles may be a useful tool for the study on the generation mechanism of PMSE.

PMSE人工电子加热和过冲实验的初步研究

极区中层夏季回波(PMSE)是发生在极区中层顶附近的一种异常强大的雷达回波,它具有明显的分层现象,加热有时能引起过冲现象.电波环境特性及模化技术国家重点实验室从2006年开始开展PMSE加热实验,通过三年的PMSE观测及加热实验,观察到PMSE回波强度具有明显的分层现象,并且层数之间变化迅速.另外本文也得到PMSE加热特征曲线OCC(Overshoot Characteristic Curves)图,回波功率随高度变化的剖面图、回波强度随时间的变化图,存在明显的过冲现象.本文开展的PMSE加热实验研究,为将来我国独立开展PMSE研究打下了一定的基础.

GPS信号在极区中层顶PMSE尘埃层的衰减分析

极区中层夏季回波(PMSE,Polar Mesosphere Summer Echoes)是通过雷达在高纬当地夏季中层顶附近探测到的异常强大雷达回波,发生PMSE现象的区域属于尘埃等离子体范畴,现在已经在1290 MHz处用雷达观测到PMSE现象。GPS系统卫星的L2频率为1227.60 MHz,容易受到PMSE尘埃层的影响。GPS信号穿越极区中层顶时,其中的尘埃等离子体区域必然对信号产生影响。利用分层媒质方法结合ECT-02实验数据研究GPS系统L2载波信号经过尘埃层的吸收系数和信号的衰减程度,证实PMSE尘埃层能影响GPS通信。

PMSE dependence on frequency observed simultaneously with VHF and UHF radars in the presence of precipitation

Using PMSE （polar mesosphere summer echoes） observations in combination with particle flux measurements obtained with detectors onboard the Geostationary Operational Environmental Satellite （GOES） a special condition is shown for the occurrence of rare observed UHF PMSE. When electron flux observed from GOES satellites show a decrease, then after being in the presence of precipitation UHF PMSE occurs. The heating effect on PMSE is small when the UHF electron density is enhanced at 90 km due to particle precipitation. We analyzed and compared the frequency dependence of PMSE under the condition of high energy particle precipitation in July of 2004 and 2007 at well separated frequencies （224 and 930 MHz） at the same site, height, and time. The frequency index varies with height and time. At different heights, the maximum as well as the minimum value of volume reflectivity at VHF is greater than that at UHF with 2 to 3 orders of magnitude. A new qualitative method for the analysis of dust distribution is used by analyzing the relationship between volume reflectivity and frequency index. In agreement with the results of the model it is shown that dust particles of smaller size generally did not occur at the edges, instead they occurred in the middle PMSE regions.

Exploring the occurrence rate of PMSE-Es by Digisonde at Tromsø

Polar mesosphere summer echoes(PMSE)are observed simultaneously with Digisonde and EISCAT VHF radar.The phenomenon of irregular Es layers is called PMSE-like or PMSE-Es(Polar Mesosphere Summer Echoes-Es)and has some relationship with real PMSE.In this paper,the characteristics of irregular Es layers at 80–100 km were observed by Digisonde at Tromsøduring 2003–2014 are statistically analyzed with ionograms.The diurnal,day-to-day and year-to-year variations and discrepancies of occurrence rate between PMSE and PMSE-Es are compared with the statistical results observed by Esrange MST radar(ESRAD),and the reasons are discussed.The results show that the trends in the occurrence rate of PMSE-Es are similar to the trends in the occurrence rate of PMSE,but there are some notable differences.The occurrence rate of PMSE-Es is much lower than the occurrence rate of PMSE.The minimum value of PMSE-Es appears 1–2 hours earlier than the minimum value of the PMSE occurrence rate,while PMSE-Es appear earlier than PMSE in the year.In addition,there is a significant positive correlation between the annual average occurrence rates of PMSE and PMSE-Es.PMSEEs is a relatively important occurrence in the polar mesopause.Analysis of its characteristics can provide new ideas and methods for studying the formation mechanism of PMSE.

Characteristic analysis of layered PMSEs measured with different elevation angles at VHF based on an experimental case

Polar Mesosphere Summer Echoes(PMSEs)are very strong radar echoes observed at altitudes near the polar summer mesopause.One of the essential properties of these radar echoes is that they can give useful diagnostic information about the physics of the scattering process.In this paper,the related characteristics of PMSEs measured with the European Incoherent SCATter Very High Frequency(EISCAT VHF)224 MHz radar on 13–15 July 2010 are studied at different elevation angles from 78°to 90°.It is found that the PMSEs peak power and strongest PMSEs average power occur at the same elevation angles.Also interesting is that the strongest PMSEs occur at off-vertical angles when a PMSEs has a layered(multilayer)structure.And reflection may have more significant effects on PMSEs when there are double or multilayer PMSEs.Possible explanations regarding these observations are discussed.

极区中层夏季回波火箭探空观测的个例分析

利用仅发生极区中层夏季回波(Polar Mesosphere Summer Echoes,PMSE)现象时的ECT-02火箭探空数据,反演出电子数密度和尘埃电荷数密度。这些典型的极区中层顶的基本参量为研究PMSE提供了良好的数据基础。通过分析得出了极区中层顶区域属于弱电离、弱耦合尘埃等离子体的结论。根据电子数密度扰动分析PMSE现象发现,电子数密度的扰动与PMSE有密切的联系,扰动强烈的地方回波就强,扰动弱的地方回波就弱,或者不发生PMSE现象。

南极中山站DPS-4电离层测高仪的中层夏季回波统计分析

本文应用DPS-4型数字式电离层测高仪观测数据研究南半球极区中层夏季回波现象(PMSE)。通过对E层和Es层异常特征的分析,证实在南半球中频和高频频段能够观测到PMSE-Es现象,并发现其与北半球PMSE出现率的季节性变化、日变化及半日变化等规律性变化类似,但存在一定差异。最后分析讨论了这些差异,并通过极光卵图解释日变化及半日变化等规律性变化。

极区夏季中层顶尘埃分层的锐边界结构研究

火箭探空实验观测结果显示,极区夏季中层顶尘埃等离子体分层中存在着稳定的锐边界结构。本文采用了流体力学方程组和尘埃粒子自洽电荷变化模型,从尘埃等离子体电动力学的角度出发,利用数值模拟研究了尘埃分层结构中尖锐边界形成的物理过程。物理分析和数值模拟结果表明,中层顶区域存在的带电冰晶粒子在等离子体及电磁力等相互作用下,很容易形成一种在时间和空间上存在长时间,稳定的局域结构,这个结构可以用来解释我们观测到的一些实验现象。

极区中层夏季回波与频率关系的初步分析

研究不同频率的雷达体在不同时间和地点测量的极区中层夏季回波(Polar Mesosphere Summer Echoes,PMSE)体反射率,发现雷达体反射率与工作频率的4次方成反比,即产生PMSE回波的散射体的雷达散射截面与频率的4次方成反比,这种频率依赖关系不同于传统湍流理论.最后提出了PMSE实验和理论研究的新方法.

极区夏季中层顶区域尘埃粒子参数的研究

采用轨道受限运动方法研究了极区夏季中层顶区域的尘埃粒子电荷数与尘埃粒子半径。利用尘埃等离子体充电理论,建立了尘埃粒子充电方程模型,得到尘埃粒子充电时尘埃电荷数和半径的比值。然后结合ECT02实验数据,分析了发生极区中层夏季回波现象时极区中层顶区域尘埃粒子电荷数和半径的比值,并得到尘埃粒子的半径以及尘埃粒子所带电荷量。结果表明,极区中层顶区域的尘埃粒子平均所带电荷不到一个,它的半径约为20nm。

极区中层夏季回波反射特性随频率变化的研究

极区中层夏季回波(PMSE)是发生在夏季极区中层顶的一种异常强大的雷达回波。在极区中层顶区域存在大量的带电尘埃粒子,并出现明显的分层结构。采用分层介质波传播理论,分别分析频率在53.5 MHz,224 MHz,931 MHz情况的信噪比。结果表明,利用分层介质理论得到的信噪比在53.5 MHz得到的结果与实验结果非常类似,并且随频率的增加,雷达信噪比明显减弱,与实验统计结果一致,可见利用分层介质理论是解释PMSE产生机制的又一重要理论结果。

极区中层夏季回波与偶发E层关系的初步研究

极区中层夏季回波(PMSE,Polar Mesosphere Summer Echoes)是发生在当地夏季极区中层顶附近的一种异常强大的雷达回波。利用电离层测高仪观测到的频高图来确定极区中层夏季回波偶发E层(PMSE-Es,Polar Mesosphere Summer Ech-oes-Sporadic E)PMSE-Es现象,进而研究南北半球PMSE现象。利用南极中山站数据结合新的统计方法给出了1999至2003年PMSE-Es出现率季节性变化,与北极对应年的PMSE出现率对比发现:它们的结果趋于一致,特别是在2002年,它们的出现率均明显偏低。这表明PMSE-Es与PMSE现象可能具有一定的相关性,将来可以利用电离层测高仪观测PMSE,监测全球变暖的环境问题。

极区中层冬季回波在224MHz的统计特性分析

基于224 MHz欧洲非相干散射甚高频雷达(European incoherent scatter very high frequency radar,EISCAT VHF radar)在2003—2014年间所观测的极区中层冬季回波(polar mesosphere winter echoes,PMWE)数据,分别从出现率、持续时间、高度分布、日变化、季节变化方面分析讨论了PMWE的平均时空特征,并对国际上PMWE与太阳和地磁活动的相关关系理论中存在的一些问题进行了讨论.结果表明:PMWE出现的几率非常低且持续时间普遍较短,其平均出现率为3.26%,每次出现的平均持续时间为67 min;高度分布范围主要在62~70 km,且在66~67 km高度范围内出现率最高;PMWE大多出现在白天,极少出现在夜晚,且11月份的出现率较高,12月份的出现率非常低.本文的研究为解释PMWE形成的物理机制提供了有价值的参考.

基于新型数据分析软件的极区中层强雷达回波研究

该文利用极区中层异常回波及云粒子数据提取分析软件(PMEC_DEAS)处理雷达回波及云粒子数据集,并进行回波特性研究。以通过PMEC_DEAS分析的短期和长期极地中层夏季回波(polar mesosphere summer echoes,PMSE)和极地中层云(polar mesospheric clouds,PMC)数据为例,研究了PMSE出现率与PMC之间的相关性。研究发现短期的PMSE出现率和PMC之间的相关性不显著,长期的双层PMSE出现率与PMC之间呈正相关关系。这表明双层PMSE与PMC密切相关,这与现有的结论一致。以此可以看出,PMEC_DEAS可以有效地适应所研究事件的复杂特征变化,并具有良好的鲁棒性。此外,利用PMEC_DEAS软件分析所得的数据具有更好的稳定性和兼容性,与目前的主流数据分析软件相比更具便捷性和实用性。

双麦克斯韦分布下极区中层尘埃粒子带电研究

在大功率微波照射下,极区中层夏季回波(PMSE)会立刻消失,该现象被称为极区中层加热现象.在大功率微波照射极区中层时,电子在微波电场加速下产生的定向运动速度与热运动速度可以比拟,极区中层的尘埃等离子体服从双麦克斯韦分布.基于双麦克斯韦分布下尘埃粒子充电理论给出极区中层尘埃粒子的电荷分布,比较了大功率微波对极区中层加热前和加热时,尘埃粒子电荷以及极区中层电子浓度的变化.结果表明,采用大功率微波装置加热极区中层会影响电子对尘埃粒子的充电进而导致电子浓度变化,这对解释极区中层加热现象具有重要意义.