North-South Asymmetry of the Interplanetary Magnetic Field Magnitude and the Geomagnetic Indices

Data of the daily interplanetary magnetic field (IMF), and the geomagnetic indices (aa, Ap, Kp, and DST) have been used to examine the asymmetry between the solar field north and south of the heliospheric current sheet, over the period (1975-2013). It important to note that during the positive polarity epochs: (T) refers to Toward the South of the heliospheric current sheet (Southern Hemisphere), and (A) refers to Away from North of the heliospheric current sheet (Northern Hemisphere). While, during the negative polarity epochs the opposite will be happened. The present study finds no clear indication of the presence of north-south asymmetry in the field magnitude, and also there is no magnetic solar cycle dependence that is evident. During the considered period, the north-south asymmetry for the considered parameters reaches maximum values around the declining phase or near to the minimum of the solar cycle. The geomagnetic indices have a clear asymmetry during the positive solar magnetic polarity period (qA > 0) and have a northern dominance during cycles (22 & 23) and southern dominance during cycles (21 & 24). From the power spectrum density, the considered parameters showed significant peaks which appeared in the north-south asymmetry but the 10.7 yr solar cycle was absent. In addition, the main periodicity of the asymmetry may be 5.2, 4.0 and 3.3 years that exist in the parameters with higher confidence levels. Finally, one can conclude that the asymmetry of the interplanetary parameters and the geomagnetic indices may provide multiple causes for producing the observed asymmetric modulations of cosmic rays.

An analysis of interplanetary sources of geomagnetic storm during November 7-8, 1998

We analyzed the properties of the solar wind appeared during November 7–8, 1998. Results show that the spaceship ACE spotted a shock (hereinafter referred to as the first shock) at 07:33 UT, November 7. The sheath appeared from the first shock to 22:00 UT November 7. A magnetic cloud-like (MCL) was observed during the period from 22:00 UT November 7 to 11:50 UT, November 8. Another shock was observed at 04:19 UT, November 8 (the second shock). It is apparent that the second shock has entered the rear part of the MCL (MCL_2), though the former part of the MCL (MCL_1) was not affected by the second shock. The main phase of the geomagnetic storm is split into three steps for the convenience of SYM-H index analysis. Step 1 covers the period from the sudden storm commence (SSC) at 08:15 UT, November 7 to the moment of 22:44 UT, November 7. Step 2 starts from 22:44 UT, November 7 and ends at 04:51 UT, November 8. The last step runs from 04:51 UT, November 8 to 06:21 UT, November 8. Step 2 has played a key role in the main development phase of the geomagnetic storm. Analysis of the solar wind properties associated with the main phase shows that the three steps in the main phase have sheath, MCL_1, and MCL_2 as their respective interplanetary source. Specifically, the sheath is covered by the solar wind data from 07:33 UT to 22:00 UT, November 7, MCL1 by the solar wind data from 22:00 UT, November 7 to 04:19 UT November 8, and MCL_2 by the solar wind data from 04:19 UT to 05:57 UT, November 8. MCL_1 had a strong and long lasting so UTh directed magnetic field, allowing it to play a key role in the development of the main phase. MCL_2 made a much smaller contribution to the main development phase, compared with MCL_1.

特大地磁暴的一种行星际源:多重磁云

20 0 1年 3月 31日观测到的大的多重磁云 (Multi MC)事件造成了第 2 3周太阳峰年 (2 0 0 0～ 2 0 0 1 )最大的地磁暴 (Dst=- 387nT) .通过分析ACE飞船的观测数据 ,描述了这个多重磁云在 1AU处的磁场和等离子体特征 .并且根据SOHO和GOES卫星的观测资料 ,认证了它的太阳源 .在这次事件中 ,由于多重磁云内部异常增强的南向磁场 ,使之地磁效应变得更强 ,它大大的延长了地磁暴的持续时间 .观测结果与理论分析表明 ,多重磁云中子磁云的相互挤压使磁云内的磁场强度及其南向分量增强数倍 ,从而加强了地磁效应 .因此 ,研究认为多重磁云中子磁云之间的相互压缩是造成特大地磁暴的一种机制 .此外 ,研究发现形成多重磁云的日冕物质抛射 (CMEs)

南海磁场特征研究

建立客观的磁力△T异常,获得可信的磁力△Z_⊥异常、居里面成果,在此基础上开展综合地质地球物理研究,对于解决南海资源等相关的地质、地球物理问题意义重大.本文汇集我国历年在南海取得的磁力实测资料,重新处理、校正、整合,特别是追溯南海周边的国际地磁台的日变资料进行日变改正,形成的南海磁力△T异常,其资料品质得到了极大提高.采用全磁纬变倾角化极技术,获得磁力△Z_⊥异常,其与实测证实的磁性海山、海岛有非常好的匹配关系,建立起可以直接用于反演处理解释的南海磁力△Z_⊥异常.选择磁力△Z_⊥异常的小波多尺度分解四阶逼近,采用单一磁性界面反演技术进行深度反演,获得居里面又称磁性底界面.建立了认识、解释南海的磁场基础体系,证实了南海基性岩浆岩分布区与磁力△Z_⊥异常的正磁异常高密切相关,区域性的磁力△Z异常负磁异常区可能与居里面深度相关.

行星际磁场B_y分量对磁尾场向电流的控制作用

利用Cluster卫星的磁场探测数据及ACE卫星的行星际磁场(IMF)探测数据,研究了IMF B_y分量(IMF|B_y|<10nT)对磁尾等离子体片边界层(PSBL)区场向电流发生率和密度的影响.研究显示:与IMF B_y分量为负时进行比较,IMF B_y分量为正时场向电流的发生率更高,约55.6%;当IMF|B_y|>4nT时场向电流发生率占总发生率的77.4%;场向电流发生率随IMF|B_y|的增大而增大,且具有很好的线性相关关系,当IMF B_y分量为正时,相关性更好;场向电流密度也随IMF|B_y|的增大而增大,同样具有很好的线性相关关系,当IMF B_y分量为正时,相关性更好.以上结果表明,IMF B_y分量对磁尾场向电流的产生和变化具有很强的控制作用,并且昏向IMF变化与场向电流变化的关系更加密切.

磁暴主相多阶发展行星际起因的初步分析

本文利用1998-2006年与磁云有关的80起中强磁暴（Dst＊≤-50nT），对其主相期间不同发展阶数磁暴的行星际起因进行了统计分析．重点研究了鞘区磁场单独作用、磁云本体单独作用、鞘区与磁云共同作用以及其他复杂行星际结构在磁暴主相多阶发展中的相对重要性，并对导致磁暴主相增加一阶的行星际起因做了初步分析．统计结果表明：（1）有一半以上的中强磁暴主相具有多个发展阶段，其中一阶磁暴和多阶磁暴（包括二阶和二阶以上磁暴）在中等磁暴（-100nT％Dst＊≤-50nT）中所占比例分别为53．8％和46．2％，在强磁暴（Dst＊≤一100nT）中所占比例分别为42．6％和57．4％；（2）随着磁暴主相发展阶数的增加，磁暴主相的平均持续时间也随之延长；（3）鞘区磁场单独作用、磁云本体单独作用、鞘区与磁云共同作用、磁云与其他行星际结构共同作用都可能引起磁暴主相的多阶发展；（4）有46．5％的多阶磁暴是由鞘区磁场与磁云本体共同作用引起，有34．9％的多阶磁暴是由鞘区磁场单独作用和磁云本体单独作用引起，其余的多阶磁暴是由其他复杂行星际结构引起；（5）在鞘区磁场单独作用的事件中，鞘区磁场结构是影响磁暴主相多阶发展的重要因素之一；（6）磁暴主相的多阶发展与晨昏电场Ey、行星际磁场Bx南向分量的发展密切相关，随着Ey和Bx阶段性的发展，磁暴主相也呈现多阶发展的趋势，且每阶Dst’极小值与该阶Eymax和Bxmin有很好的线性相关性，线性耦合方程分别为Dst＊min=-34．62—11．89×Eymax和Dst＊min=-5．90＋8．50×Bxmin。