TY  - JOUR
A1  - Asari, Seiki
A1  - Wardinski, Ingo
T1  - On magnetic estimation of Earth's core angular momentum variation
JF  - Journal of geophysical research : Solid earth
N2  - We study systematically the estimation of Earth's core angular momentum (CAM) variation between 1962.0 and 2008.0 by using core surface flow models derived from the recent geomagnetic field model C(3)FM2. Various flow models are derived by changing four parameters that control the least squares flow inversion. The parameters include the spherical harmonic (SH) truncation degree of the flow models and two Lagrange multipliers that control the weights of two additional constraints. The first constraint forces the energy spectrum of the flow solution to follow a power law l-p, where l is the SH degree and p is the fourth parameter. The second allows to modulate the solution continuously between the dynamical states of tangential geostrophy (TG) and tangential magnetostrophy (TM). The calculated CAM variations are examined in reference to two features of the observed length-of-day (LOD) variation, namely, its secular trend and 6year oscillation. We find flow models in either TG or TM state for which the estimated CAM trends agree with the LOD trend. It is necessary for TM models to have their flows dominate at planetary scales, whereas TG models should not be of this scale; otherwise, their CAM trends are too steep. These two distinct types of flow model appear to correspond to the separate regimes of previous numerical dynamos that are thought to be applicable to the Earth's core. The phase of the subdecadal CAM variation is coherently determined from flow models obtained with extensively varying inversion settings. Multiple sources of model ambiguity need to be allowed for in discussing whether these phase estimates properly represent that of Earth's CAM as an origin of the observed 6year LOD oscillation.
KW  - Core
KW  - Earth rotation
KW  - Inversion
KW  - Geomagnetic field
KW  - rapid variations
KW  - Geodynamo
Y1  - 2015
U6  - https://doi.org/10.1002/2014JB011458
SN  - 2169-9313
SN  - 2169-9356
VL  - 120
IS  - 10
SP  - 6740
EP  - 6757
PB  - American Geophysical Union
CY  - Washington
ER  -