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.     

S_q发电机电流的逐日变化和S_q指数

用中国地磁台站的资料,研究了S_q逐日变化的形态学特征,用理论模型计算了磁层环电流、部分环电流、场向电流、磁尾电流、Chapman-Ferraro电流的地磁效应.在消除了这些磁层电流体系的影响之后,得到了电离层潮汐风发电机电流产生的磁场S_q变化.对1973年的资料研究表明,S_q发电机电流的逐日变化主要表现在强度上,即使在磁扰期间,也可以分离出形态稳定的S_q变化.由此提出了一种新的地磁指数——S_q指数,用来描述S_q发电机电流强度的逐日变化.     

An inspection of the long-term behaviour of the range of the daily geomagnetic field variation from comprehensive modelling

This paper attempts to reveal whether long-term trends in the ionosphere are reflected in the amplitude range of the geomagnetic daily variation recorded at ground level. The smooth and regular variation observed in the magnetograms on magnetically quiet days is induced by the ionospheric currents flowing in the dynamo region. So it is likely that trends in the conductivity or in the dynamics of this region could produce changes in the current densities, and consequently in the range of the geomagnetic variation. The crucial aspect is how to separate the changes produced by the geomagnetic activity itself, or by secular changes of the Earth's magnetic field, from the part of the variation produced by factors affecting trends in the ionosphere, which could have an anthropogenic origin. To investigate this, we synthesized for several geomagnetic observatories the daily ranges of the geomagnetic field components with a comprehensive model of the quiet-time, near-Earth magnetic field, and finally we removed the synthetic values from the observed ranges at those observatories. This comprehensive model accounts for contributions from Earth's core, lithosphere, ionosphere, magnetosphere and coupling currents, and, additionally, accounts for influences of main field and solar activity variations on the ionosphere. Therefore, any trend remaining in the residuals, assuming that all the contributions mentioned above are properly described and thus removed by the comprehensive model, should reflect the influence of other sources. Results, based on series of magnetic data from observatories worldwide distributed, are presented. Trends in the X and Z components are misleading, since the current system changes in form as well as in intensity, producing changes of the focus latitude in the course of a solar cycle and from one cycle to another. Some differences exist between the long-term trends in the Y component between the real and modelled ranges, suggesting that other non-direct solar causes to the amplitude changes of the solar quiet geomagnetic variation should not be ruled out. Nevertheless, the results also reflect some short-comings in the way that the comprehensive modelling accounts for the influence of the solar activity on the range of the daily geomagnetic variation.     

分层电离层模型中的L电流体系

本文分析了电离层风发电机理论中影响电流分布的几种主要因素,认为电离层电导率模型是最主要的影响因素。在计算太阴日变化（L）电流体系时,本文放弃了过去习惯采用的无限薄球壳的电导率模型,使用了分层电导率模型。考虑电导率随高度的变化以及电导率极大值的高度随纬度的变化,得到了与观测结果较为符合的理论L电流体系。本文的结果还指出,在处理某些全球性发电机理论问题时,不能简单地假定电离层为距地面等高度的无限薄球壳,而必须同时考虑大气潮汐振荡的特性及电导率随高度的变化。由此得出结论:发展三维电导率模型对于电离层风发电机理论是必要的。     

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.     

Polar regionSq

Geomagnetically quiet day variations in the polar region are reviewed with respect to geomagnetic field variation, ionospheric plasma convection, electric field and current. Persistently existing field-aligned currents are the main source of the polar regionSq. Consequently, the morphology and variability of the polar regionSq largely depend upon both field-aligned currents and ionospheric conductivity. Since field-aligned currents are the major linkage between the ionosphere and the magnetosphere, the latter is controlled by solar wind state, in particular, the interplanetary magnetic field, the polar regionSq exhibits remarkable IMF dependence.     

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.     

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.     

中低纬地区电离层对CIR和CME响应的统计分析

本文利用中低纬日本地区(131°E,35°N)GPS-TEC格点化数据,分析了2001—2009年间109个共转相互作用区(CIR)事件、45个日冕物质抛射(CME)事件引起的地磁扰动期间电离层的响应.结果表明,电离层暴的类型随太阳活动的变化而有不同的变化,CIR事件引发的电离层正相暴、正负双相暴多发生在太阳活动下降年,负相暴多发生在高年,负正双相暴多发生在低年;CME事件引发的电离层正相暴和负相暴多发生在高年.CIR和CME引发的不同类型的电离层暴的季节性差异不大,在夏季多发生正负双相暴.电离层暴发生时间相对地磁暴的时延大部分在-6~6h之间,但CIR引发的电离层暴时延范围更广,在-12~24h之间,而CME引发的电离层暴时延主要在-6~6h之间.中低纬的电离层暴多发生在主相阶段,其中CIR引发的双相暴也会发生在初相阶段.电离层负暴多发生在AE最大值为800~1200nT之间.CIR引起的电离层扰动持续时间较长,一般在1~6天左右,而CME引起的电离层扰动持续时间一般在1~4天左右.     

On the 18-day quasi-periodic oscillation in the ionosphere

The presence and persistence of an 18-day quasi-periodic oscillation in the ionospheric electron density variations were studied. The data of lower ionosphere (radio-wave absorption at equivalent frequency near 1 MHz), middle and upper ionosphere (critical frequencies f₀E and f₀F2) for the period 1970–1990 have been used in the analysis. Also, solar and geomagnetic activity data (the sunspot numbers Rz and solar radio flux F10.7 cm, and a_N index respectively) were used to compare the time variations of the ionospheric with the solar and geomagnetic activity data. Periodogram, complex demodulation, auto- and cross-correlation analysis have been used. It was found that 18-day quasi-periodic oscillation exists and persists in the temporal variations of the ionospheric parameters under study with high level of correlation and mean period of 18–19 days. The time variation of the amplitude of the 18-day quasi-periodic oscillation in the ionosphere seems to be modulated by the long-term solar cycle variations. Such oscillations exist in some solar and geomagnetic parameters and in the planetary wave activity of the middle atmosphere. The high similarities in the amplitude modulation, long-term amplitude variation, period range between the oscillation of investigated parameters and the global activity of oscillation suggests a possible solar influence on the 18-day quasi-periodic oscillation in the ionosphere.     

Geomagnetic signatures of sudden ionospheric disturbances during extreme solar radiation events

We performed a comparative study of geomagnetic variations, which are associated with sudden ionospheric disturbances (SIDs) caused by great X-class solar flares on July 14, 2000 (Bastille flare) and on October 28, 2003 (Halloween flare). Intense fluxes of solar X-rays and EUV radiation as well as solar energetic particles (SEP) were considered as sources of abundant ionization of the ionosphere and upper atmosphere. Flare-initiated SIDs are revealed as transient geomagnetic variations, which are generated by enhanced electric currents flowing mainly in the bottom-side ionosphere. Those so-called solar flare effects (SFEs) were studied by using of geomagnetic data from INTERMAGNET worldwide network of ground-based magnetometers. In subsolar region the SFE is mainly controlled by the flare X-rays and/or EUV radiation. We found that in the Halloween flare the contribution of X-rays was comparable with the EUV, but in the Bastille flare the EUV flux was dominant. The ionization at high latitudes is generated by the SEP, which energy flux is comparable and even exceeds the solar electromagnetic radiation in that region. It was shown that in the Halloween event the pattern of SFE is formed by a two-vortex current system, which is similar to the quiet day Sq current system. However, during the Bastille flare, the pattern of induced currents is quite different: the northern vortex shifts westward and southern vortex shifts eastward such that the electroject is substantially tilted relative to the geomagnetic equator. From numerical estimations we found that at middle latitudes the SEP-initiated geomagnetic effect becomes comparable with the effects of solar electromagnetic radiation. It was also shown that the SEP contribute to the SFE in the nightside hemisphere. The revealed features of the SEP impact to the ionosphere were found in a good agreement with the theory of energetic particle penetration to the bottom-side magnetosphere.     

Geomagnetic and sunspot activity associations and ionospheric effects of lightning phenomena at Trivandrum near dip equator

From a study of thunder/lightning observations in Trivandrum (near dip equator) for selected years between 1853 and 2005, we could find an inverse relation of the same with sunspot activity and associations with enhancements in diurnal range of local geomagnetic declination. The results seem to suggest lightning-associated modulation of E-region dynamo currents in the equatorial ionosphere and the thunderstorm activity near dip equator probably acts as a moderator to regulate electric potential gradient changes in the global electric circuit due to solar activity changes.     

中低纬度区变化地磁场的结构分析

用自然正交分量法（MNOC）分析了我国部分地磁台的变化磁场资料,得到了组成中低纬度地区变化磁场的几种主要成分,它们是电离层风发电机电流产生的S_q变化,磁扰电流产生的S_D变化,与UT有关的D_UT变化.这些成分的相对大小随季节而变,场的变幅有特定的纬度分布.     

极区Hall电流经度差异特征的统计学研究:CHAMP卫星观测

本文利用2001至2010年间CHAMP(CHallenging Minisatellite Payload)卫星标量磁力仪(Overhauser Magnetometer)观测的磁场数据,反演得到电离层霍尔(Hall)电流,并且对极区电离层Hall电流的特征进行了统计学研究.研究主要关注平静期,即重联电场小于2 mV·m~(-1)条件下,在磁纬60°至90°范围内的Hall电流在不同太阳活动、季节、磁经度、磁地方时等条件下的变化特征.研究发现:Hall电流具有明显的经度差异,在南北半球呈现显著一波经度结构,而且南北半球反相,即北半球电流密度呈现峰-谷-峰结构,而南半球呈现谷-峰-谷结构.Hall电流密度的经度结构与太阳活动紧密相关,太阳活动高年经度差异最大,太阳活动中年经度差异次之,太阳活动低年经度差异最小.研究发现,在磁地方时为10-14MLT的白天,影响Hall电流的因素主要是太阳辐射;而磁地方时为21-03MLT的夜晚,除了电导率的影响之外,可能存在其他的重要的物理过程影响着Hall电流的经度分布.本文还研究了与电流相关的焦耳热的经度分布情况,发现其在南北半球分别呈现单峰、单谷结构,经度差异亦十分明显.     

非迁移潮作用下的电离层赤道异常区单峰现象及其经度分布

当喷泉效应较弱而双峰结构发展不充分的时候,可能在赤道异常区仅能够观测到一个电子密度的峰值,称之为单峰现象.本文利用CHAllenging Minisatellite Payload卫星在2001-2010年的电子密度数据给出了单峰的发生规律,单峰在地方时早上08：00-10：00和下午16：00-19：00发生率高,发生位置在经度上呈现多波数分布,尤其在10：00-18：00明显：在分季时多呈现四波,而在冬至季时以三波为主.单峰发生多的经度,正好对应着双峰的结构特征较弱之处.究其原因,是非迁移潮的DE2和DE3分量调制了背景风场和大气发电机电场,在电场和喷泉效应减弱的经度,双峰结构难以形成时,就会表现为单峰结构.本文扩展了对单峰现象的地方时、季节和经度分布等规律的了解,明确了非迁移潮在其中施加的影响,由此,单峰同双峰现象一样可以用于研究非迁移潮对热层-电离层的作用.     

Solar cycle variations in the ionospheric Alfven resonator 1985–1995

Based on long-term observations of the resonance structure in the electromagnetic background noise spectrum (resonance spectrum structure, RSS), recorded in the frequency range 0.1–10 Hz over one complete solar cycle (11 years, from 1985 to 1995), it was found that the resonance conditions for Alfven waves in the ionosphere (ionospheric Alfven resonator) are determined at midlatitudes by the level of solar activity. RSS are regularly observed in years of minimum solar activity, and are practically absent in years of maximum solar activity. It is shown that consideration of the ionospheric Alfven resonator explains the dependence of the RSS on solar activity.     

Sq指数的周期变化分析

利用1960-1980年中国北京和广州的地磁场X分量小时值数据,根据徐文耀(1992)提出的用来描述每日Sq变化幅度的地磁活动指数的方法,计算并分析了Asq指数的周期变化特征.结果表明:Asq指数具有11年、年和半年变化等主要周期成分,与F107指数傅氏谱主要周期成分存在对应关系,表明Asq指数的周期变化与太阳辐射密切相关.然而互相关分析表明,日变幅dSq与F107的相关关系略强,这是由于Asq指数计算中每月平均ΔS_q(t)携带了部分Sq场的周期变化信息.     

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.     

Morphology of slowly-varying geomagnetic external fields — a review

The morphology of slowly-varying geomagnetic external fields (such as Sq, L, and Dst) and the production mechanisms of electric current systems for those fields are briefly reviewed to provide background knowledge of the present state of research regarding the source fields for scientists concerned with the electromagnetic induction within the earth. It is concluded that both the Sq and Dst fields seem to have sources both in the magnetosphere and the ionosphere, while the classic idea of L-field production solely in the ionosphere by the wind dynamo is still acceptable.     

激发态氮分子N*2在电离层中的作用的模拟研究

激发态氮分子N*2在电离层F区中起着重要的作用,它使F区占主导地位的O+离子的损失率增大,从而使该区的电子浓度减少. 本文利用理论电离层数值模型,通过考虑与不考虑N*2的作用,对包括1990年6月、1997年5月、1998年5月以及2000年4月磁暴事件在内的时间区间的电离层响应情形进行模拟研究,并与实测结果进行对比. 结果表明,N*2对电离层电子浓度的影响在太阳活动高年非常明显,在太阳活动低年虽有些影响,但效果并不明显,其程度远不如高年. 在太阳活动高年,不仅是磁暴期间,在较宁静期间也必须考虑N*2的影响. 而且,在考虑N*2的作用时,还与激发态振动温度Tν有关,在采用Tν=Tn（其中Tn为背景中性大气的温度）的简化处理时,所得结果与观测结果的符合程度不如对Tν进行精确计算时所得的结果好. 模拟结果还表明,太阳活动高年,N*2作用的结果主要是使150km高度以上的F区电离层电子浓度减少,而对150km以下高度的电离层电子浓度则影响不大. 另外,N*2基本不影响F2层峰高hmF2的值.