Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Free core nutation: new large disturbance and connection evidence with
  geomagnetic jerks   Variations in free core nutation (FCN) are connected with various processes
in the Earth's fluid core and core-mantle coupling, which are also largely
responsible for the geomagnetic field variations, particularly the geomagnetic
jerks (GMJs). A previous study (Malkin, 2013) revealed that the epochs of the
observed extremes in the FCN amplitude and phase variations are close to the
GMJ epochs. In this paper, a new evidence of this connection was found. The
large FCN amplitude and phase disturbance occurred at the epoch close to the
newly revealed GMJ 2011. This event occurred to be the second large change in
the FCN amplitude and phase after the 1999 disturbance that is also associated
with the GMJ 1999. Moreover, the long-time FCN phase drift had changed suddenly
in 1998--1999, immediately before the GMJ 1999, and seemed to change again at
the epoch immediately preceding the GMJ 2011. The FCN amplitude showed a
general long-time decrease before GMJ 1999, and it subsequently grew until GMJ
2011, and then seemed to decrease again. A smaller FCN change can be observed
at the epoch around 2013, which is also suspected as the GMJ epoch. The latter
confirms the suggestion that a rapid change in the FCN amplitude and/or phase
can be used as an evidence of the GMJ that is not clearly detected from the
geomagnetic observations.

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The categories of this paper are: stat
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
4
The categories of this paper are: cond-mat