Satellite Observations Of Magnetic Reconnection And Turbulence In Space Plasma

There are full of space plasma in the solar-terrestrial environment. Magnetic reconnection and turbulence are two basic physical plasma processes. Magnetic reconnection can transfer magnetic energy into plasma thermal and kinetic energy in short time period, and changes the topology of magnetic field, thus it is suggested as related many explosive phenomena, such as solar flare, magnetosphere substorm. Turbulence is an universal phenomena in the astrophysical physics, and play important role in the plasma transport and energy dissipation. Turbulence is widely believed as the important source of solar wind heating, and important effect that affect the transport of energetic particle. There are close relationship between magnetic reconnection and turbulence. Magnetic reconnection can drive turbulence and lead it full development, while turbulence play dissipation role during magnetic reconnection, and can form the topology of magnetic field and plasma condition to trigger magnetic reconnection. The study of magnetic reconnection and turbulence can help us to understand the different physical process in solar-terrestrial environment, and provide background for the modeling and prediction in space weather.The study of dynamic and structures of magnetic reconnection is critical to understand reconnection. There are rich activities, and wave-particle interaction in the reconnection region. Which wave dominates in the different reconnection region? What’s role the waves play during reconnection, trigger or mediate the reconnection process? Energetic electrons are the important offspring of magnetic reconnection. Where and how the electrons are accelerated during reconnection? What are the properties of related structures, and what their roles that they play for reconnection? Dipolarization front is believed as the new regime of reconnection. What are kinetic structures, wave properties, and scales of dipolarization front? Turbulence is universal phenomena in space plasma. What are properties of turbulence that is related magnetic reconnection? What’s the role that turbulence plays in the reconnection process? What the properties at the ion scale and electron scale turbulence? Are there breakpoints at the electron scale? Below the electron scale, what’s the scaling of spectra? Is it exponential or power law spectra? What’s the mechanism that energy dissipate at the electron scale? All these questions need us to answer. Based on Cluster data, we investigate some questions as shown above in this thesis.In the first chapter, we introduce the solar wind, terrestrial magnetosheath and magnetotail in the solar-terrestrial environment, summarize the research advancements related to magnetic reconnection and turbulence, and point the remaining questions to be resolved.In the second chapter, we introduce the instruments and analysis methods. We give a reference to Cluster spacecraft and onboard instruments, and describe the analysis methods in this thesis.In the third chapter, we study the dynamic and related structures for magnetic reconnection. Firstly, we report the wave properties in reconnection diffusion region with high β and weak guide field. We find the wave vectors are high perpendicular to the ambient magnetic field, and the observed dispersion relation is close to Alfven-whistler mode that is deduced from hot two fluid model and kinetic theory, which confirms the theory predication, in the high β and weak guide field reconnection diffusion region. Secondly, we study the electron acceleration during magnetic reconnection. We analyze two magnetic island and thin current sheet, where density depletions are in the core region of the islands and intense currents therein. Energetic electrons are only observed in the thin current sheet and in the second magnetic island. The greatest enhancement is near the core of the second island. These energetic electrons may have been first accelerated in the thin current sheet, and then trapped and further accelerated in the magnetic island by betatron and Fermi acceleration. Using Cluster observations, we identify an asymmetric reconnection exhaust with a moderate guide field in the sheath of ICME. The features of reconnection exhaust are consistent with fast reconnection predictions and previous observations. We observe enhancement of energetic electron fluxes with energy up to400keV at one pair of separatrices in the higher density hemisphere. Finally, we show the investigation of the structures related to reconnection, including flux rope and dipolarization front. We analyze two consecutive flux ropes in the same reconnection diffusion region, and suggest that the core field inside flux rope is formed by the compression of such preexisting local ambient magnetic field By, has the same direction of local By. We study multiple dipolarization fronts (DFs) were observed by Cluster spacecraft in the magnetotail, and investigate kinetic structures and wave properties. It is found that DF is thin current sheet with the scale of ion gyroradius. The magnetic energy is mainly dissipated by electrons in the DF layer. There are intense electric field and strong current in the DF. The wave activities include waves around ion gyrofrequency and high frequency whistler wave. We discuss generation mechanism of these waves. According to the DF shape, we analyze three typical DF events, and find the dawn-dusk scale with value of>3.2Re, which are much larger than the scale of BBF and the scale of DF that is estimated by Nakamura et al.[2005]. In addition, we report the tailward propagating negative DF near a reconnection region. This DF shows a transient small positive increase in the Bz component before it increases sharply, opposite to the positive DF in the earthward flow. We analyzed the structures, wave and particle around this DF.In the fourth chapter, we report the study of turbulence in different region and different scales. Firstly, we show the observations of turbulence in the high speed reconnection jet in the presence of large guide field. We found that magnetic spectrum follows Kolmogorov spectrumf5/3in the low frequency, while in the dissipation range, the spectrum has steepen scalingf-2/8. The turbulence is intermittent below the proton scale. The wave vectors of turbulence are quasi-2D in the wave vector space, and the observed dispersion relation is consistent with Alfven-whistler mode deduced from Vlasov kinetic theory. The electric field due to the anomalous resistivity provide by turbulence is close to the typical reconnection electric field in the magnetotail, which is much larger than the case without guide field. Secondly, we make statistical study solar wind turbulence at ion scale. The results prove that the turbulence is strongly anisotropic in wave vector space within universal solar wind condition. The Alfven-whistler wave mode is dominant in the solar wind turbulence. There is a clear breakpoint around ion gyroradius scale in the k spectra. A transition range is between the inertial and dissipation range. Thirdly, we use the Cluster-Search Coil (SCM) data to study the electron scale turbulence. We choose ten years solar wind data when SCM are in the burst mode, and the statistical results show that there are breakpoints in the Doppler shifted frequency fρe of electron gyroradius. Below fρe the power laws have narrow distribution, and the center is around～2.8, while above fρe, the power laws have wide distribution with the peak around-3.8, consistent with the previous observations and theory predication. We choose magnetosheath events among six years data, and investigated magnetosheath turbulence at the electron scale statistically. The results clearly prove that there are clear breakpoints at the electron gyroradius in the magnetosheath turbulence. Below the electron gyroradius, there is a new power law spectrum with slope～-5.24. All these work show the universal properties of turbulence at the ion scale and electron scale. Combined earlier observations that showed exponential-like scaling with the reported wide distribution of the slopes here, it indicates that the physics of the electron scales is possibly not universal.In the seventh chapter, we conclude the work in this thesis, and make an outlook for future work.