Preferential Acceleration of Coherent Magnetic Structures and Bursty Bulk Flows in Earth's Magnetotail

Observations indicate that the magnetotail convection is turbulent and bi-modal, consisting of fast bursty bulk flows (BBF) and a nearly stagnant background. We demonstrate that this observed phenomenon may be understood in terms of the intermittent interactions, dynamic mergings and preferential accelerations of coherent magnetic structures under the influence of a background magnetic field geometry that is consistent with the development of an X-point mean-field structure.Comment: 12 pages, 5 Postscript figures, uses agums.st

Relativistic electrons generated at Earth's quasi-parallel bow shock.

Plasma shocks are the primary means of accelerating electrons in planetary and astrophysical settings throughout the universe. Which category of shocks, quasi-perpendicular or quasi-parallel, accelerates electrons more efficiently is debated. Although quasi-perpendicular shocks are thought to be more efficient electron accelerators, relativistic electron energies recently observed at quasi-parallel shocks exceed theoretical expectations. Using in situ observations at Earth's bow shock, we show that such relativistic electrons are generated by the interaction between the quasi-parallel shock and a related nonlinear structure, a foreshock transient, through two betatron accelerations. Our observations show that foreshock transients, overlooked previously, can increase electron acceleration efficiency at a quasi-parallel shock by an order of magnitude. Thus, quasi-parallel shocks could be more important in generating relativistic electrons, such as cosmic ray electrons, than previously thought

The Electron Losses and Fields Investigation

The Electron Losses and Fields Investigation, or ELFIN, is a 3U+ space weather CubeSat that will be launching into Earth orbit in 2017. ELFIN got its start in 2012 as a participant in the University Nanosatellite Program\u27s NS8 round, funded by the AFRL. The mission was then picked up by CSLI/ElaNa and awarded joint funding from NASA/NSF in 2014, helping provide the push to prepare ELFIN for development and launch. The primary goal of the mission is to explore the mechanisms responsible for the loss of relativistic particles from Earth\u27s magnetosphere by characterizing their properties as they enter the atmosphere. ELFIN will complete this goal by measuring for the first time the full energy distribution and pitch angle resolution of precipitating electrons using a UCLA built Energetic Particle Detector. Additionally, ELFIN will fly a 3-axis Fluxgate Magnetometer to take sensitive measurements of Earth\u27s magnetic field, allowing for the detection Electromagnetic Ion Cyclotron (EMIC) waves, thought to be the primary contributor to particle losses. A strategic use of ELFIN data in conjunction with data from equatorial space weather missions (THEMIS, MMS, etc.) will allow for the development of higher fidelity space weather models to be used for the protection of ground and space assets. ELFIN has been secured a ride along with ICEsat 2 to a polar orbit, currently scheduled for launch in Fall 2017. Currently the team is rapidly finalizing designs, performing environmental tests, and executing component integration in efforts to begin the Flight Model build and get ELFIN ready for delivery

The Relationship of Magnetotail Flow Bursts and Ground Onset Signatures

It has been known for decades that auroral substorm onset occurs on (or at least near) the most equatorward auroral arc, which is thought to map to the near geosynchronous region. The lack of auroral signatures poleward of this arc prior to onset has been a major criticism of flow-burst driven models of substorm onset. The combined THEMIS 5 spacecraft in-situ and ground array measurements provide an unprecedented opportunity to examine the causal relationship between midtail plasma flows, aurora, and ground magnetic signatures. I first present an event from 2008 using multi-spectral all sky imager data from Gillam and in-situ data from THEMIS. The multispectral data indicate an equatorward moving auroral form prior to substorm onset. When this forms reaches the most equatorward arc, the arc brightens and an auroral substorm begins. The THEMIS data show fast Earthward flows prior to onset as well. I discuss further the association of flow bursts and Pi2 pulsations, in the con text of the directly-driven Pi2 model. This model directly links flows and Pi2 pulsations, providing an important constraint on substorm onset theories

Formation of Foreshock Transients and Associated Secondary Shocks

Upstream of shocks, the foreshock is filled with hot ions. When these ions are concentrated and thermalized around a discontinuity, a diamagnetic cavity bounded by compressional boundaries, referred to as a foreshock transient, forms. Sometimes, the upstream compressional boundary can further steepen into a secondary shock, which has been observed to accelerate particles and contribute to the primary shock acceleration. However, secondary shock formation conditions and processes are not fully understood. Using particle-in-cell simulations, we reveal how secondary shocks are formed. From 1D simulations, we show that electric fields play a critical role in shaping the shock's magnetic field structure, as well as in coupling the energy of hot ions to that of the shock. We demonstrate that larger thermal speed and concentration ratio of hot ions favor the formation of a secondary shock. From a more realistic 2D simulation, we examine how a discontinuity interacts with foreshock ions leading to the formation of a foreshock transient and a secondary shock. Our results imply that secondary shocks are more likely to occur at primary shocks with higher Mach number. With the secondary shock's previously proven ability to accelerate particles in cooperation with a planetary bow shock, it is even more appealing to consider them in particle acceleration of high Mach number astrophysical shocks.Peer reviewe