On detection of the free inner core nutation from VLBI data

TL;DR

This study attempts to detect the free inner core nutation (FICN) in VLBI data using spectral and wavelet analysis, but finds no definitive FICN signal, highlighting the need for improved theoretical period estimates.

Contribution

The paper explores VLBI CPO series for FICN detection and discusses the challenges and potential signals, emphasizing the need for better theoretical predictions.

Findings

Multiple periodic signals near expected FICN period

No definitive FICN detection in VLBI data

Identification of a stable 800-day oscillation

Abstract

Several attempts to discover the FICN signal in VLBI nutation series made during last years failed. In this paper, we present some results of our further steps in this direction, unfortunately not successful either. We investigated several VLBI CPO series by means of spectral and wavelet analysis. It has been shown that there are several periodic signals with close amplitude around the expected FICN period without any prevailing one that can be reliably associated with the FICN. The most interesting for further analysis is a relatively stable oscillation with period of 800 days, which is, however, beyond the intervals predicted in other studies cited above. It seems to be necessary to improve theoretical estimates of the FICN period to make its search in the observational data more promising.