Observational Study Of The Dipolarization Fronts In The Earth's Magnetotail

The Earth's Magnetotail is an important ingredient of the magnetosphere.Many phenomena happened in the magnetotail,such as substorms,have greatly influence on human life.Dipolarization fronts(DFs)are crucial ingredients of substorms as they may dissipate energy and accelerate particles.In this paper,we conduct a multi-faceted study of the DFs through the satellite observations.The full text is divided into six chapters.The first chapter mainly introduces the structure and related background of the magnetosphere,the characteristics of the DFs and the coordinate system commonly used in the magnetic layer physics.The second chapter mainly introduces the Cluster satellites and MMS satellites,as well as the calculation methods we need to use,Minimum Variance Analysis(MVA)and Timing method.The third chapter mainly studies the small-scale structure of the DFs by the observation data of the Cluster satellite.Previous studies suggest that DF is about 1-3RE wide in the dawn-dusk direction.Recent kinetic simulations suggest that DFs may break up into small-scale structures as it propagates toward Earth.Motivated by this simulation,we revisited the scale size of DFs in the dawn-dusk direction by using Cluster observations in the years of 2001-2004,when the inter-distance among Cluster spacecraft was between 200 and 2000 km.We chose DFs that were detected by more than one spacecraft and estimated the radii of these DFs by a simple geometry analysis,which is based on the difference among the DF normals observed by different spacecraft.We found a few DFs whose dawn-dusk sizes are only a few ion inertial lengths.These values are much smaller than the values obtained from the previous studies.We suggest that these small-scale DFs were either formed as a result of breaking up of large-scale DFs,or observed at their initial phase when the DFs were only a few ion inertial lengths in the dawn-dusk direction.The fourth chapter mainly studies the different acceleration mechanisms at the DFs by the observation data of the MMS satellites.In this section,we analyze the 156 DFs observed by the MMS satellites at the Earth's magnetotail,statistically study the electron betatron acceleration and Fermi acceleration at these DFs,and quantify the contribution of different acceleration mechanisms to electron acceleration.The fifth chapter mainly explores the vertical current sheet(CSs)through the observation data of the MMS satellites at the magnetotail.Some vertical CSs were a few electron inertial lengths thick and were converting energy from magnetic field to plasma.The study of these electronic inertia length vertical CSs is very important for fast flow related energy conversion.The sixth chapter summarizes the work of the full text.