The Investigation Of Jupiter's Magnetosphere

Jupiter is the largest planet in the Solar system,and it has the strongest magnetic field and the fastest rotation rate among the eight planets.The magnetized Solar wind modulates Jupiter's magnetosphere,which is similar to the magnetosphere of the Earth.The boundary of Jupiter's magnetosphere far exceeds the Galileo satellites'orbit,therefore the magnetospheric activity is not only associated with the solar wind,but also associated with satellite.Waves and reconnections in the magnetosphere produce energetic particles to bombard the Jupiter's atmosphere,which leads to the Jupiter aurora.The aurora region can be divided to three distinct regions based on their location and physical processes:the main oval emissions,the satellite footprint emissions,and the polar emissions.Now people belived that the main oval emissons is closely related to the corotating broken,the footprint reflect the interaction between magnetosphere and satellites,and the ploar emissions are more complex,they reflect the physical process in the middle and outer magnetosphere.The previous studies on the Jupiter's magnetosphere are introduced at the beginning of the thesis.We improves the stationary model,and investigates the Jupiter's magnetosphere based on such model.Although humans have the concepts that the polar aurora is caused by the plasma activities in the middle and outer magnetosphere,there remain debates on the detailed mechanisms.In this thesis,a simple but reasonable mechanism is proposed to explain the polar emissions.The polar emissions is caused by the distortion of corotated magnetic field lines in the outer magnetosphere.Analyses of numerical simulation based on the differential rotation theory show that the region in the outer magnetotail(about 54Rj to 59Rj)forms a voluted shape.It generates a current about several hundred thousand amperes which is injected into the polar ionosphere and interacts with neutral particles,resulting in bright spots in the auroral oval.Based on these results,it is suggested that disturbances in different regions generate different spots in the polar emissions,and the brightness of the spots are related to the amplitude of disturbances.The Europa's aurora also attracts us.The Europa embedded in Jupiter's magnetosphere interacts with the rapidly corotated intrinsic magnetic field,which forms the Europa's wake in the Jupiter's aurora.Therefore,the evolution of the associated flux tube can be traced by the Europa's wake.A numerically simulation is performed to explore the evolution of a Europa's perturbed flux tube.Because the scale of the flux tube is very small compared with the magnetosphere,the theory of thin filament is suitable in this study.The results of our simulation showed that dragged by the Europa for 720s,the upstream magnetic flux tube is transformed into a stretched magnetic flux tube which is rotated with an angle of about 4° in the equatorial plane.Then this flux tube is accelerated by the magnetic tension.It relaxes to the initial state during the following 2160s,with the induced current attenuating from 9×105A to 0.The results show the footprint of Europa occupied only about 1?2 longitudes,which is in consistent with the ultraviolet images taken with the space telescope imaging spectrograph.The total energy of Europa's wake is estimated to be around 2.3x1013J,one tenth of that of Io's wake.It explains why the wake of Europa is shorter than that of Io.Moreover,the flux tube in the Jupiter's magnetosphere shows a complex behavior due to the Solar wind pressure and centrifugal force.The origin of the no-load magnetic flux tube is identified in this thesis.We find Caudal's model is unstable in the outer magnetosphere.Caudal's model is consistent with observation with low magnetic latitude(?<50°),while it is misordered with high magnetic latitude(??50),especially in the distant tail.The nonconservation of entropy in space plasmas is caused by the change of magnetic reconfiguration as well as nonadiabatic processes.The entropy parameter PV5/3,where P is plasma pressure and V is the volume of a closed flux tube containing one unit of magnetic flux,is widely used to describe the plasma transport processes,and the stability and dynamics of the magnetosphere can be also reflected by the entropy parameter.In this thesis,the distribution of entropy parameter in the stable magnetosphere of Jupiter is figured out with the method which was used to analyze Earth's plasma sheet.The results show that the entropy parameter increases between 5 Rj to 55 Rj and then decreases slowly.It means that the magnetosphere is unstable beyond 55 Rj.The distribution of the entropy parameter including the effects magnetic reconnection directly caused by the solar wind pressure indicates that the tailward plasmoid and Jupiterward flux tube are caused by the local reconnection,which is related to the local plasmoid instability not to the solar wind pressure.The inconformity with the observation in the outer magnetosphere implies that Caudal's model needs to be improved.The model is modified with the coordinate transformation method to change the distribution of the magnetic vector potential so that the magnetic field lines can be stretched in the equatorial plane.Compared with the old model,the improved model is similar at the low magnetic latitude but more consistent with the observation at the high magnetic latitude.