Multiscale dynamics of magnetotail reconnection and substorm

Magnetic reconnection is a fundamental and universal multiscale process in space plasmas, which is responsible for the conversion of magnetic energy into plasma heating, formation of fast plasma jets and acceleration of high-energy particles. Reconnection is responsible for explosive events in astrophysical plasmas and in the solar corona, operating in the solar wind and in planetary magnetospheres. In the Earths magnetosphere, reconnection leads to large-scale explosive perturbations in the magnetotail (substorms) that have various important effects for magnetosphere dynamics and profound consequences for the functioning of the human society known as Space Weather. In the Earths magnetosphere one has the unique possibility to investigate the reconnection process in space plasma in situ. Currently, the ambitious multispacecraft project MMS (Magnetospheric Multi-Scale mission) is in progress to address reconnection physics down to electron inertial scales which includes a complementary theoretical program with numerical simulations. Four identical MMS probes can distinguish spatial and temporal variations at unprecedentedly small scales using superior quality instruments. MMS new observational capabilities allow to develop semi-analytical and numerical models of the reconnection process and tools for its remote sensing, and also to investigate some of its important global substorm-related consequences. These are the goals of the current project where we suggest to combine theoretical analyses (analytical and PIC/MHD simulations) with experimental investigations using MMS and other available spacecraft observations to: (1) Develop the first semi-analytical multi-scale model of steady reconnection (covering electron, ion and MHD scales), test it on PIC simulation results and compare to MMS observations. (2) Based on this model, develop an algorithm of inverse problem solution to obtain/reconstruct basic parameters of the reconnection process from observations of spacecraft traversing through the reconnection region; validate the algorithm using the PIC simulation results and test it using MMS observations. (3) Study the processes near the reconnection separatrix far from the reconnection line to understand their relationship to the structure of the multi-scale reconnection region; investigate contributions to severe plasma sheet boundary motions from reconnection activity and from effects of the Substorm Current Wedge (SCW) system growing during substorms; develop methods to sense remotely basic reconnection parameters during distant separatrix crossings. (4) Investigate plasma sheet dynamics related to reconnection-produced flow bursts (BBFs) and substorm current systems on meso- and macro-scales using spacecraft observations and global MHD simulations, study flow braking and particle injections into the inner magnetosphere. (5) Investigate wave-particle interactions in reconnection-produced flow bursts which may provide electron heating and precipitation into the ionosphere and form an auroral image of the flow burst. (6) Provide a global context support of MMS reconnection studies, investigate multi-point multi- scale observations of magnetotail dynamics during intense substorms using adaptive magnetospheric modeling and ground-based monitoring tools, including a novel method to compute regional auroral electrojet characteristics.

Magnetic reconnection is a universal multiscale process in space plasmas, responsible for the conversion of magnetic energy into plasma heating, formation of fast plasma jets and acceleration of high-energy particles. Reconnection is responsible for explosive events in astrophysical plasmas, in the solar corona, operating in the solar wind and in planetary magnetospheres. In the Earth's magnetosphere, reconnection leads to large-scale explosive perturbations in the magnetotail (substorms) that have various important effects for magnetosphere dynamics and profound consequences for the functioning of the human society known as Space Weather. In the Earth's magnetosphere one has the unique possibility to investigate the reconnection process in space plasma in situ. Currently, the ambitious multispacecraft project MMS (Magnetospheric MultiScale mission) is in progress to address reconnection physics down to electron inertial scales which includes a complementary theoretical program with numerical simulations. Four identical MMS probes can distinguish spatial and temporal variations at unprecedentedly small scales using superior quality instruments. We used MMS' new observational capabilitiess to develop semi-analytical and numerical models of the reconnection process and tools for its remote sensing. In conjunction with Cluster, THEMIS and low-altitude spacecraft, as well as with ground magnetometer and all-sky imager observations we also investigated some of reconnection important global substorm-related consequences. Our main achievements are: (1) Construction of a pilot electron magnetohydrodynamic model of steady reconnection, and applied it to MMS data to reconstruct basic parameters of the reconnection process from observations of spacecraft traversing through the reconnection region. (2) Development of a remote sensing scheme as an alternative method to infer the temporal/spatial changes of the magnetotail reconnection, and applied the method to study the processes near the reconnection separatrix far from the reconnection line to understand their relationship to the structure of the multiscale reconnection region. (3) Identification of meso-scale flow bursts (BBFs) that are produced by reconnection and those related to ballooning-interchange instability, clarified their relation to the global magnetotail (re)configurations (global magnetotail dipolarization and local magnetic field minima), to the substorm current system (global R1/R2 current system and local contributions to the system) and to the specific auroral forms (beads, pseudo-breakups and substorm onset). (4) Investigation of wave-particle interactions in the flow bursts due to whistler waves, which appeared to play an important role in energy exchange between different parts of the electron distribution function and provide precipitation into the ionosphere. (5) Discovering the signatures of plasma sheet bubble intrusion into the inner magnetosphere in the form of strong step-like increases of energetic proton flux in the nightside auroral zone accompanied by depleted loss-cone of energetic electrons. (6) Studying the evolution of the active magnetotail current sheet and associated electron acceleration and field-aligned currents using conjugate multiscale multi-point (six spacecraft) Cluster-MMS observations.