二维电离层发电机理论模式及其初步应用

在地理坐标系下推导出二维电离层发电机理论方程,采用逐线迭代法求解得到全球二维电离层发电机电流函数,进而得到电离层发电机电流和电场.模式中使用的电导率是根据外部经验模式给出的背景大气和电离层参数,采用理论公式计算得出;输入的中性风场和磁场分别由HWM93和IGRF2000模型给出,该电离层发电机理论模式很好地给出了全球Sq电流形态及电离层E层发电机电场的基本特征.利用该模式研究了外部模式风场以及地磁场随高度的变化对模拟结果的影响,发现在90~180 km高度上,风场随高度变化对电流影响较大,而地磁场影响较小;重点模拟研究了地磁平静时期,Sq电流涡旋中心位置和总电流强度的变化规律,初步研究发现,电流中心位置在地理纬度±30°附近,不同的地方时电流随地磁纬度线平行移动,且南北半球两个电流涡中心电流强度之和变化不大.分析发现这种规律与发电机高度上的磁场总强度及地磁倾角的全球分布有很好的相关性.     

磁扰日的L电流体系

用电离层风发电机理论,对不同的电导率模型分别计算了磁静日和磁扰日期间不同月相的理论L电流体系。磁静日的L电流主要分布在纬度0°-60°之间的白天一侧,与平均太阴月的L电流相比,白天一侧的电流强度增大了1.2-1.7倍,而夜间减小到十分之一。磁扰日的L电流体系在高纬度区形成特征的电流分布（L^p）。磁扰日期间,极光带电导率的增大不仅影响极光带和高纬度地区的电流分布,而且使中低纬度的L电流增强了20-30％,使赤道电急流增强约20％,并使中低纬电流涡的焦点向高纬移动了4°左右。     

海洋和电离层发电机对佘山台L的影响

本文在文献[1]的研究基础上进一步分析海洋和电离层发电机对佘山台L的影响。资料分别按月、季节和年以及太阳活动性分组进行的细致分析,结果表明海洋发电机对Z分量的L有一稳定的影响,L的季节变化主要起源于电离层发电机。L的海洋部分不随太阳活动性改变,太阳活动对L的影响比对S的小。     

磁层-电离层-热层耦合的模式计算和分析

对磁层-电离层电动耦合和电离层发电机两种效应进行了模式计算,并对所得的一些耦合现象作了综合讨论.结果表明,在中低纬和赤道区的电离层和地磁研究中必须考虑磁层-电离层耦合效应向中低纬区的穿透和屏蔽;潮汐发电机效应对极光区（电导率增高时）的作用也值得重视.这两效应的特征和相对重要性随磁暴的发展阶段而异,在高低纬区也各不相同,但都有明显的晨昏不对称性.此外,弱磁扰对中低纬电离层形态的影响也不容忽视.     

磁层-电离层电动耦合的中纬电离层效应

本文通过对1982年磁扰期间琼中、北京两站地磁X分量变化的分析,证实了磁层-电离层电动耦合对中纬电离层电流的影响.分析发现:磁静、磁扰条件下的平均日变化中,两站X分量变化在白天有反向的趋势.这表明它们分处于与动力效应对应的电离层发电机电流圈中心之南北两侧.在磁暴主相期间,X分量变化形态与之明显不同,两站地磁南北分量有同向变化,且变幅相近,甚至有时北京站△X更大.对环电流能量增长指数R小于-25nT/h的21次事件所作的时序叠加分析（以R最负时为零时）进一步证明,这种同向变化是普遍存在的.两站零时之△X大小相近,相关系数高达0.98.该同向变化与R指数突然变负密切相关. 以上对比表明,与发电机电流造成两站X分量反向变化不同,同向变化是磁层源高纬扰动电流向中低纬直接穿透的结果.本文对动力和电动耦合两种过程的不同进行了初步讨论.     

电导率日夜不均匀性对磁层-电离层电场耦合过程的影响

本文用随时间变化的对流模式,讨论了电导率日夜不均匀性对磁层-电离层耦合过程及大尺度场向电流日变化形态的影响,以Senior-Blanc随时间变化的简单模式为基础,计入电导率日夜变化加以发展,对驱动势随时间变化为阶梯函数的情况进行了讨论。修正模式表明电导率日夜不均匀性对磁层-电离层弛豫过程产生影响,在不同地方时,二区场向电流发展状况不同,达到平衡时间也各异。在某些条件下,中午前后甚至可能达不到平衡。模式计算给出的电位及场向电流图象与观测基本特点相符。这说明S-B模式反映了电场耦合中的主要物理过程,也表明电离层电导率日夜变化的调制作用。     

不同太阳活动及地磁条件下的电导率分布变化

电离层电导率在不同的太阳活动和地磁条件下会发生变化. 本文通过中性大气经验模式NRLMSISE_00（Neutral Atmosphere Empirical Model_2000，简称NRLMSISE_00）和电离层经验模式IRI_2001（International Reference Ionosphere_2001，简称IRI_2001）计算电离层的电子、离子碰撞频率以及电导率，并简要讨论了120 km和300 km高度上的电导率在不同季节、不同太阳活动和地磁指数下的经纬分布. 结果显示，电导率的分布与日照密切相关，且随太阳活动的变化而变化. 磁暴时电导率随地磁活动的变化相对于随太阳活动的变化要小，在120?km高度，磁暴期间电导率在低纬地区和高纬地区发生不同变化，且Pedersen电导率和Hall电导率变化趋势相反，向两极靠近，电导率变化幅度略有增长；在300?km高度上，磁暴对低纬地区和高纬地区电导率的影响要比120?km处大，Pedersen电导率和Hall电导率变化趋势相同，且越向两极靠近电导率的变化幅度越大.     

不同能谱沉降电子对极区电离层的影响

利用极区电离层自洽模型,考虑沉降电子引起的电离,计算了极区电离层的高度积分电导率和F层电子浓度,模拟了不同能谱分布的沉降电子对极区电离层的影响.研究发现不同能谱分布沉降电子对电离层电导率的影响不大,在能通量一定的情况下,平均能量是影响电导率大小的决定因素.而能谱对F层电子密度影响较大,随着平均能量的增加,能谱对电子浓度的影响越显著.在平均能量大于1 keV（甚至更低）时,修正的麦克斯韦分布谱能明显地增强F层电子浓度.     

Sq发电机电流的UT变异性及其地面磁场的重建

本文用不同经度的7对中低纬台站水平磁场分量H,求得1965年随世界时（UT）变化的S_q指数（一种描述S_q电离层发电机电流强度的地磁指数）.结果表明,S_q发电机电流不仅有显著的逐日变化,而且有很大的UT变化.UT变化主要表现在电流总强度的强弱和电流涡焦点纬度移动两方面,这意味着决定发电机过程的太阳潮汐风场和电离层电导率随UT而变.用求得的S_q指数重新构造出的S_q变化与观测值符合得较好,它不仅显示出S_q幅度逐日变化的特点,而且还能复现出S_q形态的某些逐日变异性.     

单层模型对GNSS海啸电离层扰动探测的影响分析

本文全面分析了电离层单层模型高度以及投影函数对GNSS海啸电离层扰动探测的影响.利用GNSS计算的电离层扰动绝对空间分布位置随单层高度变化而变化,但对同颗卫星而言,其相对空间分布位置随单层高度变化较小.采用投影函数将倾斜方向的电离层扰动转化到垂直方向上,可以消除海啸传播方向垂直平面外的不一致性;由于电离层扰动存在水平梯度,不能消除海啸传播方向垂直平面上的不一致性.为了减弱单层模型参数对GNSS海啸电离层扰动探测的影响,在数据处理时,除了选择最大电子密度高度作为单层模型高度,还应当对每颗卫星单独进行分析.     

A study on three-dimensional structures of the ionospheric dynamo currents induced by the neutral winds simulated by the Kyushu-GCM

Three-dimensional structures of the ionospheric dynamo currents are examined using the neutral winds in a general circulation model of the middle atmosphere at Kyushu University. A quasi-three-dimensional ionospheric dynamo model is constructed assuming an infinite parallel conductivity in the ionosphere. This model is able to simulate both the equatorial electrojet and the global Sq current system successfully. The simulated results reveal that the equatorial electrojet is confined in quite narrow latitudes around the equator accompanied with meridional current circulations and satisfies a non-divergent structure mainly within the E region. A vertically stratified double layered structure is seen in the east–west current density near the focus latitude of the global Sq current system. It is shown that the stratified structure mainly consists of the east–west Hall current associated with the eastward wind of zonal wavenumbers 1 and 2 in the lower altitudes and the westward wind of zonal wavenumber 2 in the upper altitudes. The day-to-day variation of the neutral winds can significantly vary the induced ionospheric dynamo current system, which is recognized as changes of the focus latitude and/or the maximum value of the equatorial electrojet.     

Influence of seasonal variation of neutral winds on the coupling between North and South Hemispheres in a realistic Earth main field

The neutral wind dynamo contributes significantly to the ionospheric electrodynamics, and the variation of the neutral winds thus affects the ionosphere. Here we study the effects of the seasonal variation of the winds in a realistic Earth main field. The two-dimensional ionospheric dynamo equation is expressed in the framework of a revision of the International Geomagnetic Reference Field (IGRF) under the assumptions of equipotential field lines and conservation of current. A revision of IGRF and typical u...     

The correlation between the variation in ionospheric conductivity and that of the geomagnetic Sq field

Effects of the solar activity on the geomagnetic Sq field were studied by examining the correlation of the Sq amplitude in the Y-component with the sunspot number or height integrated Pedersen and Hall conductivities of the ionosphere at Kakioka, Chambon La Foret and Port Moresby for a period of 21 years. It was found that solar activity dependence of the Sq amplitude is almost explained by the effect of the local ionospheric conductivity if the month is fixed. That is, the solar activity dependence in each month is mainly caused by the local conductivity. However, the amplitude is clearly small in winter for the same conductivity value. This is probably due to the seasonal difference of the neutral winds driving ionospheric dynamo currents or to the magnetic effect of the field-aligned currents connecting both hemispheres driven by the asymmetric dynamo action in the ionosphere.     

电离层S_q发电机理论的研究和数值模拟

本文回顾了近百年来（１８８９－１９９０）电离层发电机理论中Ｓｑ电流体系的研究进展，分别阐述了Ｓｑ电流体系的研究意义、获得Ｓｑ等效电流体系的正演和反演方法、给出了主要代表学者的研究成果及方法，并对Ｓｑ发电机理论存在的问题和需要进一步研究的课题进行了讨论，可以看出Ｓｑ等效电流体系研究虽然取得了很大进展，二维理论也在日渐完善，但三维发电机研究无论在理论上和计算方法上都还有改进的余地，如何最大程度上合理地解释Ｓｑ的变化规律，并与磁层物理和大气动力学联合起来综合考虑是今后三维理论工作所必须解决的问题。     

Numerical analysis of global ionospheric current system including the effect of equatorial enhancement

A modeling method is proposed to derive a two-dimensional ionospheric layer conductivity, which is appropriate to obtain a realistic solution of the polar-originating ionospheric current system including equatorial enhancement. The model can be obtained by modifying the conventional, thin shell conductivity model. It is shown that the modification for one of the non-diagonal terms (Σ_θφ) in the conductivity tensor near the equatorial region is very important; the term influences the profile of the ionospheric electric field around the equator drastically. The proposed model can reproduce well the results representing the observed electric and magnetic field signatures of geomagnetic sudden commencement. The new model is applied to two factors concerning polar-originating ionospheric current systems. First, the latitudinal profile of the DP2 amplitude in the daytime is examined, changing the canceling rate for the dawn-to-dusk electric field by the region 2 field-aligned current. It is shown that the equatorial enhancement would not appear when the ratio of the total amount of the region 2 field-aligned current to that of region 1 exceeds 0.5. Second, the north-south asymmetry of the magnetic fields in the summer solstice condition of the ionospheric conductivity is examined by calculating the global ionospheric current system covering both hemispheres simultaneously. It is shown that the positive relationship between the magnitudes of high latitude magnetic fields and the conductivity is clearly seen if a voltage generator is given as the source, while the relationship is vague or even reversed for a current generator. The new model, based on the International Reference Ionosphere (IRI) model, can be applied to further investigations in the quantitative analysis of the magnetosphere-ionosphere coupling problems.     

磁暴期间太阳风-磁层-电离层间的耦合过程

本文用行星际和地面磁场以及电离层资料,讨论了三次磁暴期间高、中纬电离层电场对太阳风和磁层内变化的响应。 分析表明,当IMF的B_x分量由北向转为南向时,太阳风驱动的磁层对流变化能直接反映出高纬电离层电位的变化。但持续南向的B_x再次增强时,太阳风输入的主要能量耗损于内磁层过程;电离层的响应表现为一个弛豫过程。当B_x由南转北时,环电流的消失对电离层的作用同样有弛豫的特点。此时,驱动电位已撤消,环电流是维持电离层电位的唯一外源。 本文用电路类比及简单模式法结论对上述几种实测情况进行了讨论。     

Global electrical currents

Summary The atmospheric electrical structure of the earth is postulated to be controlled by a motivating force in the lower ionosphere which is produced by interaction between neutral atmosphere tidal circulations and the ionospheric plasma in the presence of the earth's magnetic field. Associated electric fields power the dynamo currents through the Hall effect with a resulting development of a gross electric potential distribution in the lower ionosphere. Asymmetries in these hemispheric potential distributions result in exospheric current flows in lowL-shells and larger differences in potential produced by dynamo return current flows in high magnetic latitudes result in strong currents through highL-shells between auroral zones. Vertical thunderstorm currents with their associated lightning discharges effectively connect the earth to a low potential region of the dynamo circuit and thus supply the earth with an average negative charge which motivates a leakage tropospheric electrical circuit. In addition, the dynamo currents maintain the magnetic polar regions at different potentials with a resulting electrical exchange with the solar wind through the earth's near space. These considerations indicate that observed electrical and variable magnetic phenomena near the earth are all part of a single comprehensive electrical current system.This paper was read byH. Dolezalek in an abbreviated form supplied by the author.