GEM: The Timing of Plasma Sheet Flows Relative to the Onset of Various Modes of Magnetospheric Response to the Solar Wind

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

This project focuses on the use of plasma and magnetic field data from the NASA Themis mission in conjunction with a large variety of other, publically available data to study plasma flows in the magnetotail and their association with various types of geomagnetic activity. The primary objective is to determine the onset times of plasma flows and a variety of other signatures of magnetic and auroral activity and to obtain a statistically reliable time sequence of events that can be used to infer the order of physical processes that cause different types of activity. To accomplish these goals a number of lists of onset times will be generated for a variety of phenomena known to occur during geomagnetic activity. These include pseudo-breakups, substorm onsets, poleward boundary intensifications, quasi-periodic substorms (sawtooth events), and steady magnetospheric convection. For each type of magnetic activity a number of signatures will be examined including auroral brightening, auroral activation, auroral expansion, onset of polar magnetic substorm, onset of Pi 2 activity, start of mid-latitude positive bays, start of field-aligned currents at synchronous orbit, and onset of synchronous dipolarization. Each onset will be characterized by a set of parameters such as location of observation, magnitude of change during initial perturbation, and state of the solar wind. Different onsets will be associated to establish discrete events consisting of a sequence of phenomena. Probability distributions of time delays between different onset times will be used to establish the typical delays and their variability. Combination of all of these delays provides the important time sequence used to infer causality. This work is of value to the field of magnetospheric physics because it would help resolve the outstanding controversy in magnetospheric physics about which physical process causes the onset of the magnetospheric substorm. In particular it should answer the question of which direction in the tail disturbances propagate after substorm onset. As a statistical study of a large number of events it would provide greater confidence in the conclusions than have previous event studies. The work would also help understand how plasma flows and magnetic flux transport in the tail are organized in different modes of response of the magnetosphere to the solar wind. The database will be made available through the Virtual Magnetic Observatory at UCLA. The project will involve graduate students and an undergraduate research assistant.