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Variations in free core nutation (FCN) are connected with various processesin the Earth's fluid core and core-mantle coupling, which are also largelyresponsible for the geomagnetic field variations, particularly the geomagneticjerks (GMJs). A previous study (Malkin, 2013) revealed that the epochs of theobserved extremes in the FCN amplitude and phase variations are close to theGMJ epochs. In this paper, a new evidence of this connection was found. Thelarge FCN amplitude and phase disturbance occurred at the epoch close to thenewly revealed GMJ 2011. This event occurred to be the second large change inthe FCN amplitude and phase after the 1999 disturbance that is also associatedwith the GMJ 1999. Moreover, the long-time FCN phase drift had changed suddenlyin 1998--1999, immediately before the GMJ 1999, and seemed to change again atthe epoch immediately preceding the GMJ 2011. The FCN amplitude showed ageneral long-time decrease before GMJ 1999, and it subsequently grew until GMJ2011, and then seemed to decrease again. A smaller FCN change can be observedat the epoch around 2013, which is also suspected as the GMJ epoch. The latterconfirms the suggestion that a rapid change in the FCN amplitude and/or phasecan be used as an evidence of the GMJ that is not clearly detected from thegeomagnetic observations.

Free core nutation: new large disturbance and connection evidence with geomagnetic jerks