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航天局Themis使命的等离子体和磁场数据，结合其他各种各样的、可通过实验获得的数据，研究磁尾中的等离子体流动及其与各种地磁活动的联系。其主要目的是确定等离子体流的起始时间以及磁活动和极光活动的各种其他特征，并获得统计上可靠的事件时间序列，可用于推断引起不同类型活动的物理过程的顺序。为了实现这些目标，将为地磁活动期间已知发生的各种现象生成一些开始时间列表。这些包括伪分裂，亚暴发作，极向边界增强，准周期性亚暴（磁层事件），和稳定的磁层对流。对于每一种类型的磁活动的一些签名将被检查，包括极光增亮，极光激活，极光扩张，极磁亚暴的开始，Pi 2活动的开始，中纬度正海湾的开始，同步轨道上的场向电流的开始，以及同步偶极化的开始。每一个开始都将以一组参数为特征，如观测位置、初始扰动期间的变化幅度和太阳风的状态。不同的开始将被关联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延迟及其可变性。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学领域具有价值，因为它将有助于解决磁层物理学中关于哪种物理过程导致磁层亚暴爆发的悬而未决的争议。特别是它应该回答的问题，在亚暴开始后，在尾部扰动传播的方向。作为大量事件的统计研究，它将比以前的事件研究提供更大的结论置信度。这项工作还将有助于了解等离子体流动和尾部磁通量传输是如何以磁层对太阳风的不同响应方式组织起来的，该数据库将通过加州大学洛杉矶分校的虚拟磁观测台提供。 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.