行星际磁场（IMF）By分量对磁正午前后区极光嘶声发生率的调制

利用南极极点站（磁纬约７５°）１９８６年３１－３８ｋＨｚ频率的ＶＬＦ波数据和卫星观测的ＩＭＦＢｙ分量数据，分析研究了ＩＭＦ晨昏分量Ｂｙ对高纬ＶＬＦ极光嘶声统计发生率周日分布的影响。结果发现，Ｂｙ对极光嘶声的统计发生率的磁地方对（ＭＬＴ）分布有明显的调制作用。磁正午前后的ＶＬＦ统计发生率不对称，Ｂｙ为正，午后发生率大于午前，Ｂｙ为负，午前发生率大于午后，Ｂｙ极性对夜侧ＶＬＦ发生频次的磁地方时分布也有     

航天简讯

1990年7月25日入轨的美航宇局和美国空军合作的一颗“播撒和观测辐射效应”卫星(CRRES)在空间把24个管装的化学元素(钡和锂),在磁层中释放,同太阳等离子体激励发生作用,特殊云区产物类似人们在两极看到的极光。为了精确观测此现象,曾用探空火箭向马绍尔群岛空间探测。当卫星上化学元素播撒后,在中美、北美和加勒比海上空出现彩色纷呈的光亮,这些彩     

极光带电急流产生声重波的效率

对大气中声重波的产生源的效率作了分析计算。结果显示,不同源的效率相差很大,而且还随频率、离原的距离和方向,以及不同的波动参量而变。对于极光带电急流产生声重波的源,即洛伦兹力和焦耳加热两个源来说,产生近场声重波的效率以洛伦兹为高、对于沿极光带电急流平面的运场区声重波而言,焦耳加热的效率高得多。但对垂直于极为带电流平面的速度波动则洛伦兹力的产生效率高得多;对于沿极光带电急流平面的法向的远场区内的所有声重波参量而言,洛地兹力的产生效率高得多。      

超声激励薄液膜Faraday波形成机理

针对35 kHz超声激励薄液膜形成的Faraday波,采用实验和有限元仿真,对Faraday波的形成机理进行探究。建立超声激励下的两相流计算模型,采用计算流体力学（CFD）方法对Faraday波的形成过程进行有限元仿真,通过分析相图和流线图,探讨Faraday波的形成机理,得到Faraday波的振动频率约为超声激励频率的1/2。液体惯性的存在,导致超声激励与液体表面波存在不断变化的相位差,相位差变化周期约等于2个超声激励周期。通过35 kHz超声激励薄液膜实验,在薄液膜表面观察到排列整齐的Faraday波图案,通过测量Faraday波的波长,得出实验获得的Faraday波频率约为超声激励频率的1/2,与有限元仿真结果一致。      

用场向电流的观测结果研究高纬电离层电场

本文从Triad卫星观测到的场向电流日变化的统计结果出发, 利用场向电流日变化的付里叶级数展开和简单模式法分别求出电导率均匀时和极光带电导率增强时高纬电离层电位的分析解.结果表明, 电场集中在极光区是由2区场向电流引起的.在本文所用的场向电流分布形式下, 加上Pederson电导率的升高。极光区Hall电导率的增大反而有助于电场向中纬穿透.|AL|≥100γ时, 场向电流分布对对流圈位置西向旋转起一定作用, 但极光带Hall电导率的变化是造成大角度旋转的主要原因.Perdson电导率的增大, 对旋转角无影响.结果还表明, 在不考虑电导率日夜不均匀时, 由于场向电流复杂的日变化, 也可出现对流圈的晨昏不对称性.以上的电场分布形态, 与观测的电场形态基本相符。      

基于U-net的紫外极光观测极光卵形态提取

极光卵形态提取是极光研究的重要手段.如何提高强干扰背景下的紫外极光图像极光卵形态提取精度,目前仍是一个难题.本文提出一种基于深度学习语义分割模型U-net的方法,实现了对极光卵形态的高精度提取.在Polar卫星紫外极光观测数据的实验结果表明,该方法相比于已有算法精度更高,对完整型极光卵和缺口型极光卵图像均能得到更加精确...     

磁化等离子体中斜传播的离子孤波

近几年卫星空间电场测量经常证认出局地非线性离子静电波,它们可能与极光粒子加速有直接关系。这些静电波被认为或者是离子声波模的演化,或者是静电离子逥旋波模的演化结果。本文研究了磁场中斜传播小振幅离子非线性波的演化,得到非线性Schrodinger方程。结果表明离子声孤波和离子迴旋孤波都是可能的。计算结果与卫星S(3-3)电场测量比较,可以很好说明部分测量结果。      

带有平行电场的Alfven激波样结构——极光粒子加速机制

动力Ａｌｆｖｅｎ波在邓散和反演耗散作用下,非线性化成类似激波样的结构,它携带的平行电场为极光粒子加速提供了新机制,Ｆｒｅｊａ卫星观测到相似的孤立Ａｌｆｖｅｎ结构。     

质子辐射带辐射中心区域模型

利用AP-8和CRRESPRO质子辐射带模式数据库, 比较了二者在磁赤道面上计算结果 的差异并给出其差异原因. 利用AP-8模式数据库数据, 建立起质子辐射带函数形式的辐射中心区域模式, 包括各能道全向微分通量峰值所对应的L值(L_c) 随能量E的变化模式以及各能道全向微分通量峰值J_max随能量E的变化模式. 利用RBSP A卫星REPT望远镜在磁赤道面上的高能质子观测数据, 分别与 AP-8模式、CRRESPRO模式及本文所得辐射中心区域模式计算结果进行比较, 发现在78.9, 102.6和208MeV三个能道上, RBSP A卫星观测所得各能道全向微分 通量明显偏大, 而L_c与AP-8或本文辐射中心模式所得结果基本一致; RBSP A卫星也观测到CRRESPRO Quiet模式所得的隐性第二质子辐射带结构.      

大气行星波对LF和VLF无线电波传播的影响

本文采用最大熵谱估计方法,对1985-1987年三个冬天,在东半球(20°S—65°N、13°E—141°E)白天观测的LF和VLF电波相位、幅度、卫星观测的Ly-α射线通量及高纬上空的行星波活动等大量资料,进行了熵谱分析。观测及分析结果表明:(1)LF和VLF电波的相位具有2—2.2天、3—4天、6—12天、12—20天、20—32天周期范围的行星尺度扰动.Ly-α射线辐射通量主要具有20—32天周期范围内的波动.(2)发现在中纬地区冬天观测的LF电波幅度大的扰动与高纬60°N上空观测的行星波H_1的变化规律非常一致. 波形结构的主要峰和谷几乎完全对应,仅在时间上前者约滞后3—4天.计算给出两者的相关系数在0.65—0.85之间.根据观测事实和谱分析结果对比,作者认为LF和VLF电波相位、幅度周期在20天以上的扰动主要受太阳Ly-α辐射通量变化的控制.冬天其周期在2—20天范围内的扰动,主要受来自对流层和下平流层中激发的大气行星波的影响.     

Broadband electrostatic noise and low-frequency waves in the Earth’s magnetosphere

Broadband electrostatic noise (BEN) is commonly observed in different regions of the Earth’s magnetosphere, eg., auroral region, plasma sheet boundary layer, etc. The frequency of these BENs lies in the range from lower hybrid to the local electron plasma frequency and sometimes even higher. Spacecraft observations suggest that the high and low-frequency parts of BEN appear to be two different wave modes. There is a well established theory for the high-frequency part which can be explained by electrostatic solitary waves, however, low-frequency part is yet to be fully understood. The linear theory of low-frequency waves is developed in a four-component magnetized plasma consisting of three types of electrons, namely cold background electron, warm electrons, warm electron beam and ions. The electrostatic dispersion relation is solved, both analytically and numerically. For the parameters relevant to the auroral region, our analysis predict excitation of electron acoustic waves in the frequency range of 17 Hz to 2.6 kHz with transverse wavelengths in range of (1–70) km. The results from this model may be applied to explain some features of the low-frequency part of the broadband electrostatic noise observed in other regions of the magnetosphere.     

Impulsive plasma waves observed by DE-1 in the magnetosphere

Impulsive plasma waves (1–9 kHz) with durations less than 100 msec have been found in DE-1 wide-band electric field data (650 Hz – 40 kHz) received at Kashima, Japan. The waves are associated with a strong narrow-band ELF hiss, and were observed at geocentric distances from 3.1 to 4.9 Re (earth's radius) in the low-latitude nightside magnetosphere. Local electron densities and plasmapause locations estimated suggest that the waves were observed outside the nightside plasmapause. The waves are discussed in terms of Landau resonant trapping of magnetospheric electrons by the associated whistler-mode ELF hiss.     

Auroral Electrojet Event Associated With Magnetospheric Substorms

The auroral electrojet index is an important index in monitoring and predicting substorms. A substorms usually includes auroral breakup, auroral electrojet event marked by AE increase, energetic particle injection at geosynchronous orbit, mid-low latitude Pi2, etc. However the question whether an auroral electrojet event corresponds to a substorm remains unanswered. Using the auroral electrojet index in 2004, we analyzed five auroral electrojet events and studied their relation with substorms. The results show that there are three kinds of auroral electrojet events: (1) simultaneous rapid increase of westward auroral electrojet and eastward auroral electrojet; (2) rapid increase of westward auroral electrojet and almost unchangeable eastward auroral electrojet; (3) rapid increase of eastward auroral electrojet and almost unchangeable westward auroral electrojet. Most of auroral electrojet events correspond to substorms. However a few auroral electrojet events are not accompanied by substorms. This situation most often occurs for the auroral electrojet event in which eastward auroral electrojet dominates.      

午后极光强度与太阳风-磁层耦合函数的相关

利用1997年和1998年南极中山站多通道扫描光度计的地面观测数据和Wind卫星在弓激波上游对行星际磁场和太阳风参数的观测数据,对午后高纬极光强度与太阳风-磁层耦合函数之间的相关性进行定量研究.研究表明,午后630.0nm极光强度与太阳风-磁层耦合函数间有很好的相关,而557.7nm的相关性差一些;在考察的所有耦合函数中,午后极光受太阳风电场和能量的影响更直接;同时,行星际磁场的时钟角对午后极光也有很强的控制作用.      

黄河站和Tromso站亚暴期间热层风场观测结果

中高层大气风场探测对研究大气物理过程具有极为重要的意义，尤其是在极地地区，风场对大气结构的影响更为剧烈.针对亚暴期间中国北极黄河站和日本Tromso站上空OI557.7nm气辉层（低热层）中性风场，利用全天空法布里-珀罗干涉仪（all-sky Fabry-Perot Interferometer，all-sky FPI）探测气辉谱线的多普勒频移，反演气辉层的大气风场信息.结果表明，低热层风场平均水平在100m·s-1左右，热层风场在极地地区更为剧烈，纬度相对较低的Tromso站探测到的风速整体小于同期黄河站上空的风速.结合离子风数据，分析离子拖拽和焦耳加热对中性风的影响过程，发现极光亚暴不仅对低热层风场有增强作用，也有明显的抑制效果，但整体风向都垂直于极光弧变化.      

Planetary radio astronomy from voyager

The Planetary Radio Astronomy instruments on Voyager 1 and 2 provided new, highly detailed measurements of several different kinds of strong, nonthermal radiation generated in the inner magnetospheres and upper ionospheres of Jupiter and Saturn. At Jupiter, an intense decameter-wavelength component (between a few tenths of a MHz and 39.5 MHz) is characterized by complex, highly organized structure in the frequency-time domain and by a strong dependence on the longitude of the observer and, in some cases, of Io. At frequencies below about 1 MHz there exists a (principally) kilometer-wavelength component of emission that is bursty, relatively broadbanded (typically covering 10 to 1000 kHz), and strongly modulated by planetary rotation. The properties of this component are consistent with a source confined to high latitudes on the dayside hemisphere of Jupiter. A second kilometric component is narrow-banded, relatively weak and exhibits a spectral peak near 100 kHz. The narrowband component also occurs periodically but at a repetition rate that is a few percent slower than that corresponding to the planetary rotation rate. This component is thought to originate at a frequency near the electron plasma frequency in the outer part of the Io plasma torus (8 to 10 R_J) and to reflect the small departures from perfect corotation experienced by plasma there.The Voyager instruments also detected intense, low frequency, radio emissions from the Saturn system. The Saturnian kilometric radiation is observed in a relatively narrow frequency band between 3 kHz and 1.2 MHz, is elliptically or circularly polarized, and is strongly modulated in intensity at Saturn's 10.66-hr rotation period. This emission is believed to be emitted in the right-hand extraordinary mode from regions near or in Saturn's dayside, polar, magnetospheric cusps. Variations in intensity at Saturn's rotation period may correspond to the rotation of a localized magnetic anomaly into the vicinity of the ionospheric footprint of the polar cusp. Variations in activity on time scales of a few days and longer seem to indicate that both the solar wind and the satellite Dione can also influence the generation of the radio emission.     

极光场线上上行氧离子(O+)束驱动的静电离子迥旋波和离子声波不稳定性

本文研究了由背景热电子、背景冷质子(H+)和强各向异性氧离子(O+)束组成的模型等离子体中静电O+迴旋波和离子声波不稳定性.结果表明,低频(|ω|<σ_p,σ_p表示质子迴旋频率)静电O+迴旋波和离子声波可以由极光场线上上行O+束来激发.上行O+束可能是极光场线上低频静电不稳定性一个重要的自由能源.      

Auroral structures at Jupiter and Earth

This paper compares global structures of the aurora observed at Jupiter and Earth and our understanding of the mechanisms that produce these structures. Both planets have permanent, magnetically conjugate auroral ovals, although produced by quite different mechanisms. Both are multispectral, having been observed at X-ray, ultraviolet, visible, infrared, and radio wavelengths. The brightest structures are produced by downward accelerated electron fluxes associated with upward Birkeland (magnetic-field-aligned) currents. At both planets, the auroral forms are time variable, especially at highest latitudes. The main power source for auroral emissions is planetary rotation at Jupiter, and the solar wind interaction at Earth. Thus Jupiter's auroral structures tend to be fixed with respect to magnetic (System III) longitude while Earth's are fixed with respect to local time. Earth's auroral structure is strongly dependent on the direction of the interplanetary magnetic field (IMF). At Jupiter, no IMF dependence is known, but observations have not been sufficient to show such a dependence if it exists. A unique feature of Jupiter's auroral structure, with no counterpart at Earth, is the signature of the large (Galilean) satellites and, in the case of Io, even the corotational wake of the satellite.     

Stimulation of plasma waves in the magnetosphere using satellite JIKIKEN (EXOS-B)

The stimulated plasma wave experiment (SPW) has been successfully carried out in the plasmasphere and the magnetosphere along the JIKIKEN (EXOS-B) satellite orbit where the plasma parameters indicate wide variety of the combination of the electron number density, ranging from 1/cc to 10⁴/cc, and the electron cyclotron frequency, ranging from 6 kHz to 200 kHz.The upper hybrid resonances F_UHR usually persists for long periods up to 125 msec and the electron cyclotron resonances nF_H are stimulated at frequencies with the very high harmonic number n; sometimes, the nF_H resonance takes place for n=47.All the features of the resonances including F_On reflect the characteristics of the magnetospheric plasma that contains the energetic and non-Maxwellian components of the particles. The measurement of the plasma resonance contributes to the detection of the local electron density and the magnetic field intensity. The mode of the propagating radio waves is also determined being compared with the observed local plasma resonance frequency F_p.     

极光强扰动对中低纬电离层的影响

本文考查了120°E附近的五个中低纬电离层观测站在极光强扰动下的f₀F₂行为。共考查了从1966—1970年五年资料中AE>1400日及1969年中AE>1000日的f₀F₂行为。研究得出了与印度站链有所不同特征——在极光强扰动下120°E中低纬五站之f₀F₂均有不同程度的减小,而不是增加,并且在中纬较高纬度的满州里站之f₀F₂减小比北京站要显著。扰日后效在中、低纬区不同,低纬之武昌、广州和海南岛三站均呈现扰动过后次日上午段的f₀F₂增加,中纬较高纬度的满洲里站仍呈现f₀F₂减少。我们认为这是由于低纬区主要受赤道喷泉效应改变的影响,而中纬及亚极光纬区主要受极光强扰时产生的环球电场的直接作用结果,它反映了纬向电场耦合传递的影响。当然极光扰动时对中性大气层的能量输入亦对观测到的现象有贡献。