2010 Vol. 30, No. 4

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Aspects of global magnetospheric processes
P. Song, V. M. Vasyliūnas
2010, 30(4): 289-311. doi: 10.11728/cjss2010.04.289
Abstract(2431) PDF 669KB(1418)
Magnetospheric global modeling is a method to link observations from distant regions via physical laws and has long played a unique and crucial role in space physics. It, different from computer simulations, represents the highest level of abstraction of the physical understanding of the processes that cause observed phenomena. It results in various specific models. While it appears in the form of cartoons, it is based on and has to be qualitatively consistent with physical laws. With the advancement of computer simulations, clues to the connection between physical laws and observation can be perceived much more easily than as ever before. However, computer simulation results are highly dependent on the used boundary conditions and numerical methods which may or may not represent the reality, even if the initial conditions are properly set. Therefore, simulations can easily mislead the investigations. Furthermore, a simulation result needs to be examined using diagnostic tools, such as field line tracing and streamline tracing programs. There are uncertainties in these diagnostic methods. The errors can be very large in certain areas under certain conditions. For example, a small error may link two different field lines or stream lines. The interpretations of the simulation results can be misled by these errors. The knowledge of global modeling can be useful in identifying the inconsistencies in the simulations and the flaws in the theoretical interpretation from the simulations. This review-tutorial article outlines the principles of the global modeling and discusses the successes and flaws of several global models.
Observations of magnetic reconnection in the magnetotail associated with substorms
Y. Miyashita
2010, 30(4): 312-320. doi: 10.11728/cjss2010.04.312
Abstract(2393) PDF 466KB(1147)
Magnetic reconnection is one of the most important, dynamic phenomena in the magnetotail in terms of magnetic field line configuration change and energy release. It is believed to occur in the distant magnetotail mainly during southward interplanetary magnetic field periods and in the near-Earth magnetotail in association with substorms. In the present paper, we discuss several important issues concerning magnetic reconnection in the magnetotail associated with substorms, such as reconnection signatures, location, timing, spatial scale, and behavior, from the macroscopic, observational point of view.
Electrodynamic coupling in the solar wind-magnetosphere-ionosphere system
Hu Youqiu, Wang Chi
2010, 30(4): 321-332. doi: 10.11728/cjss2010.04.321
Abstract(2337) PDF 321KB(1885)
This paper presents a brief summary of our recent work based on global MHD simulations of the Solar wind-Magnetosphere-Ionosphere (SMI) system with emphasis on the electrodynamic coupling in the system. The main conclusions obtained are summarized as follows. (1) As a main dynamo of the SMI system, the bow shock contributes to both region 1 Field-Aligned Current (FAC) and cross-tail current. Under strong interplanetary driving conditions and moderate Alfven Mach numbers, the bow shock's contribution may exceed more than fifty percent of the total of either region 1 or cross-tail currents. (2) In terms of more than 100 simulation runs with due southward Interplanetary Magnetic Field (IMF), we have found a combined parameter f = EswPswMA-1/2 (Esw, Psw, and MA are the solar wind electric field, ram pressure, and Alfven Mach number, respectively): both the ionospheric transpolar potential and the magnetopause reconnection voltage vary linearly with f for small f, but saturate for large f. (3) The reconnection voltage is approximately fitted by sin3/2θIMF/2, where θIMF is the IMF clock angle. The ionospheric transpolar potential, the voltage along the polar cap boundary, and the electric fields along the merging line however defined they may be, respond differently to θIMF, so it is not justified to take them as substitutes for the reconnection voltage.
Global hybrid simulation of magnetic reconnection in the magnetosheath
Pang Ye, Lin Yu, Deng Xiaohua
2010, 30(4): 333-342. doi: 10.11728/cjss2010.04.333
Abstract(2559) PDF 455KB(1369)
A three-dimensional (3-D) global hybrid simulation is carried out for the generation and structure of magnetic reconnection in the magnetosheath due to interaction of an interplanetary Tangential Discontinuity (TD) with the bow shock and magnetosphere. Runs are performed for solar wind TDs possessing different initial half-widths. As the TD propagates through the bow shock toward the magnetopause, it is greatly narrowed by a two-step compression processes, a "shock compression'' followed by a subsequent ``convective compression''. In cases with a relatively thin solar wind TD, 3-D patchy reconnection is initiated in the transmitted TD, forming magnetosheath flux ropes. Multiple components of ion particles are present in the velocity distribution in the magnetosheath merging, accompanied by ion heating. For cases with a relatively wide initial TD, a dominant single X-line appears in the subsolar magnetosheath after the transmitted TD is narrowed. A shock analysis is performed for the detailed structure of magnetic reconnection in the magnetosheath. Rotational Discontinuity (RD)/Time-Dependent Intermediate Shock (TDIS) are found to dominate the reconnection layer, which and some weak slow shocks are responsible for the ion heating and acceleration.
Comparison of BBFs observed by single and multi satellites
Cao Jinbin, Cheng Chao, Ma Yuduan, Cai Chunlin
2010, 30(4): 343-348. doi: 10.11728/cjss2010.04.343
Abstract(2349) PDF 297KB(1228)
This paper, using the data of three Cluster satellites, compares the observations of Bursty Bulk Flow (BBF) by single satellite with those by multi satellites. The results indicate that there exists remarkable difference between observations of BBF by single satellite and multi satellites. The observations of BBF by a single satellite depend on its position relative to the flow channel. The difference is caused by the localization characteristics of fast flows in the plasma sheet, and can lead to diverging views about substorm and causal relations among substorm phenomena.
Auroral electrojet event associated with magnetospheric substorms
Zou Ziming, Cao Jinbin, Li Yi
2010, 30(4): 349-355. doi: 10.11728/cjss2010.04.349
Abstract(2309) PDF 214KB(1220)
The auroral electrojet index is an important index in monitoring and predicting substorms. A substorms usually includes auroral breakup, auroral electrojet event marked by AE increase, energetic particle injection at geosynchronous orbit, mid-low latitude Pi2, etc. However the question whether an auroral electrojet event corresponds to a substorm remains unanswered. Using the auroral electrojet index in 2004, we analyzed five auroral electrojet events and studied their relation with substorms. The results show that there are three kinds of auroral electrojet events: (1) simultaneous rapid increase of westward auroral electrojet and eastward auroral electrojet; (2) rapid increase of westward auroral electrojet and almost unchangeable eastward auroral electrojet; (3) rapid increase of eastward auroral electrojet and almost unchangeable westward auroral electrojet. Most of auroral electrojet events correspond to substorms. However a few auroral electrojet events are not accompanied by substorms. This situation most often occurs for the auroral electrojet event in which eastward auroral electrojet dominates.
Statistics of the interplanetary magnetic fields observed at 0.72 AU and 1 AU
Li Xiaoyu, Zhang Tielong
2010, 30(4): 356-361. doi: 10.11728/cjss2010.04.356
Abstract(2368) PDF 248KB(1353)
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.
A Review of the Ionospheric Investigations in China: Progress During 2008—2010
Wan Weixing
2010, 30(4): 362-381. doi: 10.11728/cjss2010.04.362
Abstract(2127) PDF 255KB(1360)
In the ionospheric research, various progresses have been made during the last two years. This paper reviews the recent works of Chinese scientists. For convenience, the contents include: ionospheric storms and space weather; ionospheric irregularities and scintillation; ionospheric variability; ionospheric disturbances; ionospheric response to solar eclipses; ionospheric coupling with atmosphere and lithosphere; ionospheric climatology; ionospheric modeling; and ionospheric prediction and application.
Development of the Chinese Meridian Project
Wang Chi
2010, 30(4): 382-384. doi: 10.11728/cjss2010.04.382
Abstract(2282) PDF 144KB(1544)
The Meridian Project is a ground-based network program to monitor Solar-Terrestrial space environment, which consists of a chain of ground-based observatories with multiple instruments including magnetometers, ionosondes, HF and VHF radars, Lidars, IPS monitors, sounding rockets etc. The chain is mainly located in the neighborhood of 120$^\circ$E meridian, and is thus named the Meridian Project. The Meridian Project has officially been approved and supported by the Chinese government and will be finished by the end of 2010. This report gives an overview of the Meridian Project, and reports the recent development since 2008.