极隙区粒子和电流的观测和研究

处于高纬向日面的极隙区是太阳风能量、动量和质量可以直接进入地球磁场并到达地球的近地空间的区域。本文简要介绍了极隙区的观测和研究，综述了极隙区的粒子沉降、场向电流、等离子体对流和电离层电流的特征。     

Application of the Linear Prediction filters in equatorial electrojet studies

Wiener filters are derived from the horizontal field data of two adjacent equatorial electrojet stations, Adis Ababa and Trivandrum from several sequences of quiet days. The time invariant property of the filter is established and the filter is applied to conditions marked by afternoon counter electrojet events. The prediction efficiency is shown to be consistently high. Possible uses of this technique in studies related to generating mechanisms of counter electrojet events and the day-to-day variability in electrojet currents are indicated. Inter-relationships and day-to-day variability of different components of the fields at the two stations are highlighted.     

The complex-image method for calculating the magnetic and electric fields produced at the surface of the Earth by the auroral electrojet

For studying the auroral electrojet and for examining the effects it can produce in power systems on the ground, it is useful to be able to calculate the magnetic and electric fields that the electrojet produces at the surface of the Earth. Including the effects of currents induced in the Earth leads to a set of integral expressions, the numerical computation of which is complicated and demanding of computer resources. An approximate solution can be achieved by representing the induced currents by an image current at a complex depth. We present a simple derivation of the complex-image expressions and use them to calculate the fields produced by the auroral electrojet at the surface of an earth represented by layered conductivity models. Comparison of these results with ones obtained using the exact integral solution show that the errors introduced are insignificant compared to the uncertainties in the parameters used. The complex-image method thus provides a simple, fast and accurate means of calculating the magnetic and electric fields.     

Calculating Auroral Oval Pattern by AE Index

The relationship between the auroral oval pattern, i.e., location, size, shape, and intensity, and the auroral electrojet activity index （AE index） is studied. It is found that the maximal auroral intensity is elliptically distributed, and the lengths of semimajor and semiminor axes are positively correlated to AE. The intensity along the normal of the auroral oval can be satisfyingly described by a Gaussian distribution, and the maximum and the full width at half maximum of the Gaussian distribution ave both positively correlated to AE. Based on these statistical results, a series of experimental formulas as a function of AE are developed to calculate the location, size, shape, and intensity of the auroral oval. These formulas are validated by the auroral images released by SWPC/NOAA.     

Global distributions of storm-time ionospheric currents as seen in geomagnetic field variations

To investigate temporal and spatial evolution of global geomagnetic field variations from high-latitude to the equator during geomagnetic storms, we analyzed ground geomagnetic field disturbances from high latitudes to the magnetic equator. The daytime ionospheric equivalent current during the storm main phase showed that twin-vortex ionospheric currents driven by the Region 1 field-aligned currents （R1 FACs） are intensified significantly and expand to the low-latitude region of-30~ magnetic latitude. Centers of the currents were located around 70~ and 65~ in the morning and afternoon, respectively. Corresponding to intensification of the R1 FACs, an enhancement of the eastward/westward equatorial electrojet occurred at the daytime/nighttime dip equator. This signature suggests that the enhanced convection electric field penetrates to both the daytime and nighttime equa- tor. During the recovery phase, the daytime equivalent current showed that two new pairs of twin vortices, which are different from two-cell ionospheric currents driven by the R1 FACs, appear in the polar cap and mid latitude. The former led to enhanced north- ward Bz （NBZ） FACs driven by lobe reconnection tailward of the cusps, owing to the northward interplanetary magnetic field （IMF）. The latter was generated by enhanced Region 2 field-aligned currents （R2 FACs）. Associated with these magnetic field variations in the mid-latitudes and polar cap, the equatorial magnetic field variation showed a strongly negative signature, produced by the westward equatorial electrojet current caused by the dusk-to-dawn electric field.     

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.     

地球内磁层场向电流的统计特征

利用ISEE－1和ISEE-2飞船观测的磁场数据，分析了地球内磁层场向电流的统计特征，包括场向电流的空间（L值和地方时）分布；流进和流出电离层的场向电流随地方时的变化；场向电流发生率与地磁活动水平（以AL指数表征）、行星际磁场（IMF）Bz的关系，电流强度和密度随地磁活动水平的变化等．发现，场向电流大都发生在夜间，且集中在L为6-10区域内，场向电流发生率，强度和密度随地磁活动增强而增大，行星际磁场南向时的发生率远远高于北向时的发生率．这些结果表明，内磁层场向电流的产生是太阳风和磁层、电离层间电动耦合增加的结果．     

内磁层电流体系的地磁效应

对Ⅱ区场向电流及其伴随的部分环电流和电离层电流组成的内磁层三维电流体系（PRFI电流系）的磁场效应进行了数值计算.这一三维电流体系在中低纬度地面产生的磁场呈现出特殊的纬度分布:X分量几乎不随纬度变化,Y分量随纬度增高近似呈线性变化.这些特征明显不同于对称环电流的磁场分布特征（X∝ cosφ,φ是纬度,Y=0）,也不同于DP2、S_q、L等电流体系的磁场分布特征.利用这一特征我们可以从地磁台子午链观测到的磁场扰动中分离出PRFI电流系的贡献.用1989年3月磁暴的实例检验了上述模型,观测结果与理论结果符合得很好.分析结果还表明,最大的D_st指数并不一定对应着最强的对称环电流.