NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Torque Balances on the Taylor Cylinders in the Geomagnetic Data AssimilationIn this presentation we report on our continuing effort in geomagnetic data assimilation, aiming at understanding and predicting geomagnetic secular variation on decadal time scales. In particular, we focus on the effect of the torque balances on the cylindrical surfaces in the core co-axial with the Earth's rotation axis (the Taylor cylinders) on the time evolution of assimilated solutions. We use our MoSST core dynamics,model and observed geomagnetic field at the Earth's surface derived via Comprehensive Field Model (CFM) for the geomagnetic data assimilation. In our earlier studies, a model solution is selected randomly from our numerical database. It is then assimilated with the observations such that the poloidal field possesses the same field tomography on the core-mantel boundary (CMB) continued downward from surface observations. This tomography change is assumed to be effective through out the outer core. While this approach allows rapid convergence between model solutions and the observations, it also generates sevee numerical instabilities: the delicate balance between weak fluid inertia and the magnetic torques on the Taylor cylinders are completely altered. Consequently, the assimilated solution diverges quickly (in approximately 10% of the magnetic free-decay time in the core). To improve the assimilation, we propose a partial penetration of the assimilation from the CMB: The full-scale modification at the CMB decreases linearly and vanish at an interior radius r(sub a). We shall examine from our assimilation tests possible relationships between the convergence rate of the model solutions to observations and the cut-off radius r(sub a). A better assimilation shall serve our nudging tests in near future.
Document ID
20040171523
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Kuang, Weijia
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Tangborn, Andrew
(Maryland Univ. Baltimore County)
Date Acquired
August 22, 2013
Publication Date
January 1, 2004
Subject Category
Geosciences (General)
Meeting Information
Meeting: American Geophysical Union Meeting
Location: Montreal
Country: Canada
Start Date: May 17, 2004
End Date: May 21, 2004
Sponsors: American Geophysical Union
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

Available Downloads

There are no available downloads for this record.
No Preview Available