An Operational 3-D Magnetospheric B-Field Model

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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.