An Operational 3-D Magnetospheric B-Field Model

这是NSF三年拨款的续期提案。我们建议建立一个可操作的三维磁层b场模型，以响应太阳风和行星际场条件的变化，以及磁尾和环流区域内等离子体条件的变化。新模型近似满足MHD平衡条件；它依赖于准静态时标。我们的目标是开发一个用户友好的FORTAN代码，可以根据要求被科学界使用。提出的工作是重要的，因为大多数可用的地球磁层三维b场模型相当有限：它们只代表“平均”磁层条件（例如，相对于Kp指数有序）。b场模型需要更灵活的模拟临界磁层情况，如亚暴扩展阶段后期高度拉伸的尾场线，或中性片重连事件后的“崩溃”磁尾场线。此外，场向的Birkeland电流和“开放”磁层的边界条件需要得到很好的表现。我们建议通过开发所谓的希尔默-福格特磁层磁场模型的第二代代码来实现这一目标。Hilmer 1989 !;该模型已经在之前的NSF资助下设计、编码和测试（也有其他资金的额外帮助）。Hilmer-Voigt模型的一个初步版本目前正与“Rice对流模型”和“磁层规格模型”结合使用。通过这些“应用”获得的经验使我们提出了一些主要的物理改进，其中包括：(1)用一种对太阳风撞击热压力作出反应的柔性形状取代现有的磁层顶。(2)包括“开放”磁层的磁层顶边界条件。(3)提供计算工具，包括场向Birkeland电流。(4)利用Stern的拉伸变换使磁尾和环电流近似符合准静态MHD力平衡的要求。我们提出的工作不是一个狭窄或有限的任务|我们声称，响应各种物理输入参数的用户友好的灵活b场模型是磁层物理学的一项重大成就，因为它为我们提供了数据分析和理论研究的多功能研究工具。

This is a renewal proposal for a three-year NSF grant. We propose to develop an operational three-dimensional magnetospheric B-field model for Earth's magnetosphere which responds to changes in the solar wind and interplanetary field conditions, and to changes in the plasma conditions within the magnetotail and ring-current regions. The new model approximately satisfies the MHD equilibrium condition; it is time-dependent on the quasi-static time scale. We aim at developing a user-friendly FORTAN code which can be used by the scientific community upon request. The proposed work is important, because most available three- dimensional B-field models for Earth's magnetosphere are rather limited: they represent only "average" magnetospheric conditions (e.g., ordered with respect to the Kp index). B-field models much more flexible are needed for simulating critical magnetospheric situations, such as highly stretched tail field lines in the late state of the substorm expansion phase, or "collapsed" magnetotail field lines following a neutral sheet reconnection event. Also, field-aligned Birkeland currents and boundary conditions of the "open" magnetosphere need to be well represented. We propose to achieve such a goal by developing a second- generation code of the so-called Hilmer-Voigt magnetospheric magnetic field model ?Hilmer, 1989!; that model has been designed, coded, and tested under the previous NSF grant (with the additional help from other funding as well). A preliminary version of the Hilmer-Voigt model is presently being used in connection with the "Rice Convection Model" and the "Magnetospheric Specification Model". The experience gained through those "applications" has led us to propose some major physical improvements which include the following: (1) Replace the existing magnetopause by a flexible shape which responds to the solar wind ram thermal pressures. (2) Include magnetopause boundary conditions for an "open" magnetosphere. (3) Provide the computational tools to include field-aligned Birkeland currents. (4) Use Stern's stretch transformations to make the magnetotail and ring currents approximately consistent with the requirement of quasi-static MHD force balance. The proposed work is not a narrow or limited task| We claim that a user-friendly flexible B-field model that responds to a variety of physical input parameters is a significant achievement for magnetospheric physics, in that it provides us with a versatile research tool for both data analysis and theoretical studies.