Evidence of solar signals in tree rings of Smith fir from Sygera Mountain in southeast Tibet

Abstract

Solar activity is one of the most important driving forces of the global climate and environment change. However, little is known about how this force is influencing the earth's climate system due to short solar activity records. A tree-ring chronology of Abies georgei var. smithii at Sygera Mountain in southeast Tibet was developed and used to investigate solar activity signals by spectral, wavelet and cross-wavelet analyses. The results showed that fluctuations in tree-ring data coincided well with variations in sunspot numbers. Periodicities of 5.3–5.1, 11.2–11.1, 20.5, 73, and 204.1 years may be related to solar activity of the second harmonic of the Schwabe, Schwabe, Hale, Gleissberg, and Suess cycles. The cross-wavelet analysis between tree-ring data and sunspot numbers indicated that the cross power around the 11-year solar cycle is more significant during periods of high solar activity than low solar activity, and the significant 22-year solar cycle is also found. Cross-correlation analysis between these two series showed a significant relationship with a time lag of about 13 years and a non-stationary phase relationship. We therefore propose that solar activity modulated climatic conditions and tree growth by influencing surface temperature through variations in radiation energy and monsoonal precipitation on the Tibetan Plateau.