تحليل چرخه هاي ميانگين دماي سالانه شهر زنجان

Analyzing the Cycles of Medium Annual Temperature of Zanjan City

Latent, gradual and slow cycles in different apparent and latent frequencies are one of the various types of climatic changes .some of these oscillations in a fixed period e.g. one year, are determined as monthly or seasonally mediums, some others occur as latent cycles in climatic time series. Spectral analysis is one of useful tools for searching and evaluating such these climatic changes. This method of studying the climatic changes has a considerable and wide spread acceptance in the world. However it hasnʹt used by Iranian climatologist in detail. Exploring climatic cycles particularly temperature cycles will provide the planning based on temperature-climatic data. In this paper, while introducing Spectral analysis as an accepted and efficient method for tracing latent cycles, it is tried to study and review the latent cycles in medium annual temperature of Zanjan city during the statistical period of 1956-2005(50 years). Therefore by using autocorrelation function, temperature spectrum and temperature cycles of Zanjan city were extracted. Based on the data obtained through this research, Zanjan temperature has a cycle of 2.5 years. These cycles have been in coordination with the other discovered cycles in climatic elements of other parts in the world. As the other scientists have found, the power generating this oscillation is probably the result of vertical transition of jolter from tropsfer to stratsfer with irregular return periods of 2-3 years. Keywords: Cycle, Oscillation, Spectral Analysis, Temperature, Zanjan City.