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

该项目的重点是利用美国宇航局Themis飞行任务中的等离子体和磁场数据，结合大量其他公开可用的数据，研究磁尾中的等离子体流动及其与各种类型的地磁活动的关系。主要目标是确定等离子体流的开始时间以及磁和极光活动的各种其他特征，并获得可用于推断引起不同类型活动的物理过程顺序的统计上可靠的事件时间序列。为了实现这些目标，将为地磁活动期间已知的各种现象生成一系列开始时间清单。这些包括伪分裂、亚暴开始、向极地边界加强、准周期亚暴(锯齿事件)和稳定的磁层对流。对于每种类型的磁活动，将检查一些信号，包括极光亮化、极光激活、极光扩张、极地磁亚风暴的开始、PI 2活动的开始、中纬度正海湾的开始、同步轨道上场向电流的开始和同步双极化的开始。每一次爆发都将由一系列参数来表征，如观测位置、初始扰动期间的变化幅度和太阳风的状态。不同的起点将被关联起来，以建立由一系列现象组成的离散事件。将使用不同起始时间之间的时间延迟的概率分布来确定典型的延迟及其变异性。所有这些延迟的组合提供了用于推断因果关系的重要时间序列。这项工作对磁层物理领域是有价值的，因为它将有助于解决磁层物理学中关于哪个物理过程导致磁层亚暴开始的悬而未决的争议。特别是，它应该回答在亚风暴爆发后尾部扰动传播的方向的问题。作为对大量事件的统计研究，它将比以前的事件研究对结论提供更大的信心。这项工作还将有助于理解尾部的等离子体流动和磁通量传输是如何以磁层对太阳风的不同响应模式组织起来的。该项目将涉及研究生和一名本科生研究助理。

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 howplasma 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.