Institute of Computer Science, Academy of Sciences of the Czech Republic

Period 7.8 years oscillatory modes in the monthly NAO index and temperature records and their possible phase relations

Recently, Gamiz-Fortis et al. (J. Geophys. Res. 107(D23) 4685, 2002) have detected, using the Monte Carlo Singular System Analysis (MCSSA), an oscillatory mode with the period around 7.7 years in the winter North Atlantic Oscillation (NAO) index.
Palus and Novotna (Phys. Lett. A 248 191-202, 1998) proposed an enhancement of MCSSA in which, in addition to the signal covariance structure, a complexity measure of the SSA modes is tested against surrogate data; and were able to detect a period 7.8 years oscillatory mode in long-term monthly near-surface air temperature records from several European locations.
We show that using the enhanced MCSSA the period 7.8 years oscillatory mode can be detected in the monthly NAO index, too. These modes are extracted from the raw data, their instantaneous phases are computed and their possible relations (phase synchronization and directionality of coupling, i.e., causality relations between the NAO and the temperature oscillatory modes) are studied.

This study is supported by the GA AS CR project No. IAA3042401.