Magnetic storm cessation during sustained northward IMF

Times of sustained strong northward IMF can interrupt the magnetic storm development and lead to lower levels of geomagnetic activity for many hours. During 1997–2000 we have found two events of this kind observed on November 8, 1998 and October 13, 2000. In both cases, the storms started as usual after arrival of ejecta with a southward IMF component from the Sun to the Earth, but ceased after several hours due to the onset of sustained northward IMF leading to the faster recovery process. After the passage of this so-called positive domain, the storm development started again. The heliospheric magnetic field intensity remained enhanced and nearly constant. The solar origins of the geomagnetic storm interruptions have been investigated. Tentatively they may be related to strong nonlinear Alfvйn type solitary waves excited by non-stationary coronal current variations with a characteristic time-scale of about a day.     

The auroral activity during the main phase of magnetic storms

The relationship of auroral activity indices (AE, Kp, SME) with interplanetary medium parameters during the main phase of magnetic storms is studied. For the period 1990–2020, 142 magnetic storms driven by (41) Sheath, (61) CIR, and (40) ICME events are selected. It is found that the correlation coefficient between average values of the SME index and the SW electric field for Sheath (r = 0.75) is close to correlation coefficients for CIR and ICME events. The correlation coefficient between Kp_aver&Esw_aver (r = 0.72) is higher than the correlation coefficient between AE_aver&Esw_aver (r = 0.63) at the main phase of magnetic storms induced by the Sheath events. It is shown that average values of SW dynamic pressure and IMF σB fluctuations correlate each other for all types of SW.     

Variations in polar rain flux according to IMF geometries observed by STSAT-1

We examined polar rain flux observed by STSAT-1 in the northern polar cap and compared it with solar wind parameters. We found that the differential energy spectrum of polar rain was similar to that of the solar wind for the energy range 100 eV – 1 keV, although we cannot rule out the possibility of a small amount of acceleration. On the other hand, the low-energy component of the solar wind showed no correlation and, naturally, the solar wind density had only a weak correlation with the polar rain flux. Polar rain flux in the northern hemisphere is most significant for the condition of the interplanetary magnetic field components Bz < 0, Bx < 0, and By > 0, and in this case it correlated well with the magnitude of By and Bz. For other interplanetary magnetic field conditions, the correlation was insignificant. The results are consistent with those reported previously.     

ULF wave index as magnetospheric and space-weather parameters

Waves in the Ultra Low Frequency (ULF) band owe their existence to solar wind turbulence and transport momentum and energy from the solar wind to the magnetosphere and farther down. Therefore an index based on ULF wave power could better characterize solar wind–magnetosphere interaction than K_P, Dst, AE, etc. indices which described mainly quasi-study state condition of the system. We have shown that the ULF wave index accurately characterize relativistic electron dynamics in the magnetosphere as these waves are closely associated with circulation, diffusion and energization of relativistic electrons in the magnetosphere. High speed solar wind streams also act as a significant driver of activity in the Earth’s magnetosphere co-rotating interaction region and are responsible for geomagnetic activities. In the present paper, we have analyzed various cases related with very weak (quiet) days, weak days, storm days and eclipse events and discussed the utility of the ULF wave index to explain the magnetospheric dynamics and associated properties. We have tried to explain that the ULF wave index can equally be useful as a space weather parameter like the other indices.     

1998年5月空间天气大事件的地磁场响应

地磁场与1998年5月空间大事件相对应的是5月1日至16日发生的大磁暴（k=8)。磁暴主相开始的几个小时伴随有丰富的Pc型地磁脉动，包括P c2,Pc3,Pc4等。在增暴的恢复相，甚至还有Pc5巨型脉动，在行星标磁场Bz由北向转向南向时，磁暴主相开始；南向分量达到最大值后大约2小时，地磁H分量达到最小值，恢复相开始，并且，这次磁暴与太阳风电场也存在一定的对应关系。     

关于IMF北向分量特强时的太阳风－磁层－电离层耦合

关于ＩＭＦ北向分量特强时的太阳风－磁层－电离层耦合沈长寿，资民筠（北京大学地球物理系，１００８７１）（中国艺术研究院，北京）关键词行星际磁场，太阳风－磁层能量耦合函数为检验Ａｋａｓｏｆｕ提出的能量融合函数“’在ＢＺ强北向时能否反映太阳风与磁层扰动间的...     

2000年7月空间天气大事件对地磁场的影响

2000年7月空间大事件对地磁场产生了巨大影响，7月15日至18日发生大磁暴(K=9)．磁暴为急始型，在我国地区初相期变幅有200—300nT，主相最大幅度有500—600nT，为多年来所罕见．在行星际磁场Bz由北向转向南向时，磁暴主相开始；南向分量达到最大值后大约2h，地磁H分量达到最小值，恢复相开始．并且，这次磁暴与太阳风也存在一定的对应关系。     

Statistics of the Interplanetary Magnetic Fields Observed at 0.72 AU And 1 AU

This paper presents the Interplanetary Magnetic Field (IMF) observations at 0.72 AU measured by Venus Express (VEX) and 1 AU by Advanced Composition Explorer (ACE) in 2007. The distributions of daily averages of $B$ are lognormal in both locations. The multiscale structure of the magnetic field fluctuations was described by studying the increments of $B$ over a range scales from 10 min to 21.3 hours. All the Probability Distribution Functions (PDFs) can be described quantitatively by Tsallis distribution function. On the ecliptic plane from 0.72 AU to 1 AU, the entropy index q increases with distance over all scales, indicating the intermittency of turbulence is growing. The widths of the PDFs at 0.72 AU are larger than those at 1 AU at all scales, which indicating the turbulence at 0.72 AU is more intense than that at 1 AU. This helps us understand the nature and development of the magnetic field fluctuations.