Satellite Observation Of Turbulence In Collisionless Magnetic Reconnection

The space environment between the Earth and the Sun,known as the geospace environment,is the fourth environment beyond the natural surroundings.It is influenced by solar radiation and the Earth’s magnetic field,playing a crucial role in human survival and technological advancement.Intense space weather phenomena such as geomagnetic storms and solar flares directly impact communication and navigation systems,all closely associated with magnetic reconnection and turbulence.Magnetic reconnection and turbulence are two fundamental processes in space environments,often interacting and coupling with each other.Despite advancements in understanding magnetic reconnection and turbulence,their intricate relationship remains a focal point of research in space physics,with numerous unresolved inquiries.For instance,the evolution characteristics of magnetically-driven dynamic turbulence and its modulation on energy conversion,reconnection rate,and electron acceleration heating in magnetic reconnection remain a subject of inquiry.Moreover,what are the principal features of turbulence-induced magnetic reconnection and the corresponding dynamical properties of turbulence at kinematic scales?Furthermore,what role does magnetic reconnection play in energy dissipation and distribution within dynamic turbulence,and how does it influence multiscale coupling effects?In-depth studies of the fundamental properties and dynamical processes of turbulent reconnection are of significant importance for understanding energy release processes in the geospace environment.With the launch of the Magnetospheric Multiscale（MMS）satellite,high-precision,high-resolution data provided new opportunities for studying magnetic reconnection and turbulence.This doctoral dissertation primarily focuses on the characteristics of turbulence driven by magnetic reconnection and its influence on magnetic reconnection.By utilizing the detection data from the MMS satellites,the dissertation investigates the evolutionary nature of turbulent reconnection and its role in energy conversion and energy cascade.The following are the main research findings of this thesis:1.Evolution characteristics of reconnection-driven turbulence:We investigated the features of magnetic reconnection-driven turbulence,revealing a good correspondence between intermittent intensity and the peak velocity of rapidly evolving overall flows generated by reconnection.We also found that fully developed turbulence in the inertial range exhibits a multifractal scale,while weak intermittent turbulence shows a single-fractal scale.The intermittent dissipation of magnetic energy in turbulence mainly occurs in coherent structures.Electromagnetic Electron Cyclotron Waves（ECWs）were reported for the first time in the turbulent reconnection outflow region within the Earth’s magnetotail.We found that these waves primarily concentrate near integer multiples of the electron cyclotron frequency(f_ce)and have wavelengths of approximately 100 kilometers,equivalent to several electron cyclotron radii.These waves may be driven by the gradient distribution of energetic electron phase space density（（?）f/（?）v_⊥>0）and the excitation of Electron Cyclotron Maser Instability（ECMI）.We statistically analyzed the primary factors influencing the strength of turbulent reconnection in the magnetotail.We found that inflow conditions,such as inflow Alfvén velocity(V_A,in),inflowβvalue(β_in),inflow magnetic field perturbation(dB_in),and electric field perturbation(dE_in),are the main catalysts for the evolution of reconnection into turbulent reconnection.For solar wind conditions,only the interplanetary magnetic field（IMF）cone angle and solar wind dynamic pressure showed significant positive correlations with turbulent intensity,while there was no obvious dependence between geomagnetic activity and turbulent intensity.2.Roles of reconnection-driven turbulence in reconnection:Direct evidence provided for turbulence facilitating reconnection energy conversion.By comparing magnetotail reconnection events with the same upstream plasma parameters but different turbulent amplitudes,we found that stronger turbulence produces more and smaller spatial scale coherent structures in reconnection and provides stronger energy conversion.Furthermore,turbulence has little impact on particle heating but does affect the overall kinetic energy of ions.3.Cross-scale energy cascades in turbulent reconnection:Starting from first principles and employing a scale-filtering approach,we computationally estimated the local cross-scale energy cascade and energy conversion between scales in magnetic reconnection based on observations.We found that in magnetopause reconnection,the cross-scale energy cascade rate is highest in the electron diffusion region（EDR）,where magnetic and kinetic energy cascades across scales from ion to sub-ion scales remain positively cascaded,and electrons remain unheated.Additionally,we found that the EDR plays a crucial role in promoting dissipation-scale energy cascades.In summary,we have revealed the evolutionary characteristics of turbulence driven by reconnection in terms of intermittent intensity and fractal features.We reported the rare electromagnetic ECW phenomenon in the turbulent reconnection outflow region and identified key factors influencing the intensity of turbulent reconnection.Furthermore,we have provided direct evidence of turbulence promoting energy conversion in reconnection,revealing local cross-scale energy cascades and energy conversion between scales.We also pointed out the crucial role of reconnection EDR in promoting energy cascades at dissipation scales.These research findings deepen our understanding of the dynamical processes of collisionless magnetic reconnection and turbulence,particularly in terms of energy dissipation and particle acceleration.They also contribute to a deeper exploration of the origin and acceleration of solar coronal and solar wind phenomena.Moreover,these findings help us gain a more profound insight into the physical processes occurring in the geospace environment,providing an important foundation for modeling and accurately forecasting space weather.