Synchronization between the North Sea-Caspian pattern (NCP) and surface air temperatures in NCEP

摘要

In this study, synchronous linkages of the North Sea-Caspian pattern (NCP), associated with large-scale surface air temperature series selected from National Centers for Environmental Prediction-National Center of Atmospheric Research reanalysis (NCEP-NCAR) for the region over 50 degrees W- 120 degrees E and 0- 80 degrees N are investigated via teleconnection patterns based on phase synchronization. Phase synchronization is the process by which two or more cyclic systems (or subsystems) tend to oscillate with a repeating sequence of relative phase angles. Phase synchronization is usually applied to two waveforms of the same frequency with identical phase angles in each cycle. However, the notion of phase synchronization has been introduced as an extension of classical Huygens' synchronization in the case of interacting chaotic systems if there is an integer relationship of frequency, such that the cyclic systems share a repeating sequence of phase angles over consecutive cycles. The results of the phase synchronization method are compared with those of the classical cross-correlation method in cases in which cross-correlation method shows linear spatial cross-dependency, but the phase synchronization yields nonlinear spatial phase dependency. In the analyses, teleconnection patterns derived from phase synchronization are first calculated for raw and de-seasoned data (by removing periodic components in the surface air temperature series) in year-month scale and then for the data in seasonal-scale (namely, winter, spring, summer and autumn). Teleconnection patterns calculated by phase synchronization improve the experiential intra-phase relationships between the NCP Index (NCPI) and large-scale surface air temperature series, and ensures that the major modes of mid and high Northern Hemisphere variability in climate are characterized. Statistically significant phase synchronization patterns related to geopotential dipole heights of the NCPI extending over Greenland, the Balkans, Caspian Sea basin, eastern Mediterranean, Turkey and the Middle East, and further phase synchronization patterns over the circumpolar mode, which are utilized by phase interaction of Arctic oscillation (AO) with NCP, are obtained. In addition, significant phase synchronization patterns are also obtained over Tibetan plateau-Mongolia (Gobi Desert) interacting with the Siberian high, Asiatic monsoon and the intertropical convergence zone. Copyright (C) 2007 Royal Meteorological Society