1953—2014年丽水日照时数周期演变规律

利用丽水市1953—2014年逐月日照资料，采用趋势分析方法对年代际、年际和季节日照时数变化趋势进行分析，利用Morlet小波分析和多窗口谱 (Multi Taper Method) 研究日照时数的周期特征，并重建显著周期信号，分析日照时数不同时间尺度显著周期的演变规律。结果表明：丽水日照时数呈极显著下降趋势，每10 a减少35%。夏季日照时数最多，且减少趋势最明显，其次是秋季。Morlet小波和多窗口谱分析结果均显示：年代际尺度准12 a周期最为显著，年际尺度6 a和2～4 a周期也较明显。最显著的准12 a周期信号，其振幅随时间变化具有3个明显的缓变包络。

Periodic Variation of Sunshine Duration from 1953 to 2014 in Lishui

Based on the monthly sunshine dataset from the Lishui observation station from 1953 to 2014, the trend analysis method is used to analyze the inter annual, decadal and seasonal trends of sunshine duration, and then the Morlet wavelet transform and MTM (Multi Taper Method) are applied to study the periodic characteristics of sunshine duration, and the significant periodic signals are reconstructed by MTM, to further study the less significant periods on different time scales with the oscillation time of evolution. The results show that sunshine duration exhibits very significant decline trend in Lishui, with a rate of 3.5 percent per 10 years. The maximum sunshine duration is in summer, followed by that in autumn. The Morlet wavelet and MTM analysis results show that quasi 12 year cycle is the most significant in the whole time domain, with regular alternating positive and negative oscillations and the maximum spectral density; in addition, the cycles of 6 years and 2 to 4 years cycle are also apparent. The MTM reconstruction analysis indicates that the amplitudes of quasi 12 year periodic signals vary with time, and there are three distinct and slowly varying envelopes.