Core Angular Momentum Change Data: Excess length of day in milliseconds over standard day of 86400 seconds - Jackson et al. data
Entry ID: IERS_GGFC_SBC_CAM_LOD_JACKSON

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Summary
Abstract: [Adapted from "http://www.astro.oma.be/SBC/data1.html"]

Core angular momentum (CAM) is estimated by Jackson et al. using
modelling hypotheses applied to magnetic data. CAM is then
transformed into change in the length of day (LOD). Data is expressed
as excess length of day in milliseconds over a standard day of 86400
seconds.

Modelling hypotheses:
The zonal toroidal t_1^0 and t_3^0 components of a fully
time-dependent geostrophic flow constructed under the frozen flux
hypothesis are used to estimate the core angular momentum (CAM) using
the hypothesis of Jault Gire and LeMouel (1988). The flow is
constructed using a basis of B-splines with knot spacing of 2.5
years. The CAM is then transformed into an equivalent change in the
length of the day as seen on the solid Earth by conservation of
angular momentum. The predictions only give relative changes in the
lod, therefore an arbitrary offset should be chosen in order that the
predictions agree reasonably well with the lod series from
astronomical observations. A value of 3.25 milliseconds has been added
to the predictions to give the values presented here. Three different
series are given rough, intermediate and smooth - they have different
misfits to the magnetic data. The smooth model is the preferred one.

Description of the data used for model computation :
The magnetic field and its rate of change at the core-mantle
interface was computed at 2.5 year intervals from field model ufm1 of
Bloxham & Jackson (1992)

Related URL
Link: GET DATA
Description: Excess length of day in milliseconds over standard day of 86400
seconds data in ASCII format


Link: VIEW PROJECT HOME PAGE
Description: IERS GGFC Special Bureau for the Core home page.


Parent DIF
This data set description is a member of a collection. The collection is described in
IERS_GGFC_SBC_CAM_LOD


Data Set Citation
Dataset Originator/Creator: Jackson, A., J. Bloxham and D. Gubbins
Dataset Title: Data of Core Angular Momentum Changes
Dataset Publisher: Special Bureau for the Core, GGFC, IERS
Data Presentation Form: Table
Online Resource: http://www.astro.oma.be/SBC/data1.html


Temporal Coverage
Start Date: 1840-01-01
Stop Date: 1990-12-31


Location Keywords
SOLID EARTH > CORE


Data Resolution
Temporal Resolution: 1 year


Science Keywords
SOLID EARTH >GRAVITY/GRAVITATIONAL FIELD >ROTATIONAL MOTION/VARIATIONS    [Definition]


ISO Topic Category
GEOSCIENTIFIC INFORMATION


Project
SBC >Special Bureau for the Core, GGFC, IERS    [Information]


Access Constraints
No constraints


Use Constraints
Please cite data provider.

Reference to be mentioned when data are used:
Jackson A., 1997. Time-Depency of geostrophic core surface
motions, Phys. Earth Planet. Int., 103, pp 293-311.


Keywords
CORE
ANGULAR MOMENTUM
ROTATION
LOD
LEGNTH OF DAY
IERS


Data Set Progress
COMPLETE


Data Center
Global Geophysical Fluids Center, International Earth Rotation Service    [Information]
Data Center URL: http://bowie.gsfc.nasa.gov/ggfc/

Data Center Personnel
Name: BENJAMIN F. CHAO
Email: chao at bowie.gsfc.nasa.gov
Contact Address:
Space Geodesy Branch, Code 926
NASA's Goddard Space Flight Center (GSFC)
City: Greenbelt
Province or State: Maryland
Postal Code: 20771
Country: USA



Distribution
Distribution_Media: Online (HTTP)
Distribution_Format: ASCII
Fees: None


Personnel
GENE R. MAJOR
Role: DIF AUTHOR
Email: gsfc-gcmduso at mail.nasa.gov


ANDREW JACKSON
Role: INVESTIGATOR
Contact Address:
Department of Earth Sciences
University of Leeds
Leeds LS2 9JT
UK


JEREMY BLOXHAM
Role: INVESTIGATOR
Phone: (617) 495-9517
Fax: (617) 495-7660
Email: jeremy_bloxham at harvard.edu
Contact Address:
Department of Earth and Planetary Sciences
Harvard University
20 Oxford Street
City: Cambridge
Province or State: MA
Postal Code: 02138
Country: USA


DAVID GUBBINS
Role: INVESTIGATOR
Contact Address:
Department of Earth and Planetary Sciences
Harvard University
20 Oxford Street
City: Cambridge
Province or State: MA
Postal Code: 02138
Country: USA


Publications/References
Reference to be mentioned when data are used: Jackson A., 1997. Time-Depency of geostrophic core surface motions, Phys. Earth Planet. Int., 103, pp 293-311.

Related reference:
Bloxham J. & Jackson A., 1992. Time-dependent mapping of the magnetic field at the core-mantle boundary, J. Geophys. Res., 97, pp 19537-19563.

Creation and Review Dates
DIF Creation Date: 2003-10-16
Last DIF Revision Date: 2003-10-17
Future DIF Review Date: 2004-10-16

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