Climate Oscillations in Southern Bulgaria and Solar Activity: Analysis of Annual Rings of Needle Samples

Abstract

Abstract—The main subject of the study is an analysis of time series of the width of annual rings of spruce and pine (D) that were obtained during the implementation of a scientific project supported by the Institute of Astronomy of the Bulgarian Academy of Sciences and the Ministry of Agriculture and Food in 2012–2014. The project is a continuation of our previous study (Komitov and Kaftan, 2019). Of the 45 wood samples collected in the project, only four are Pinopsidae: one is spruce (Picea), and the other three are pine (Pinus). The age of the samples is in the range of 65–129 years. We used two methods to obtain statistically significant cycles of fluctuations in the width of annual rings: T-R periodogram algorithm and wavelet analysis. Statistically significant cycles lasting 10–11, 20–22, 25, 38, and 64–68 years were confidently identified. There are solar and geophysical analogs for all of these fluctuations. Statistically significant mutual correlation relationships that take into account the time shift in the range of 0–5 years between D pine samples, temperatures, and precipitation at neighboring meteorological stations were established. There are also secondary extrema of the correlation coefficients after the mutual displacement of time series by 20–25 years. This result seems to be additional evidence of the solar–geophysical origin of the obtained dependencies.