Analyses of relationship between Loess Plateau erosion and sunspots based on wavelet transform

Abstract. Loess Plateau is one of the worst soil erosion regions in the world, which may resulted from various factors such as precipitation, land cover and land use, soil, vegetation, human intervention, as well as solar activities. The purpose of this study is to find the relationship between soil erosion and sunspot activity on the Loess Plateau, through analyses of the sunspot relative number and the long-term sediment discharge series in Longmen station in the Yellow River based on the Morlet wavelet method. In this paper, annual sediment discharge series from 1919–2008 in Longmen station and the sunspot relative number were decomposed with Complex Morlet wavelet. The results of real part, modulus and the second power of modulus showed an obvious periodic variability in sediment discharge, with 25–40 years, about 10 years, and less than 10 years scales. There are six centers of energy. From the wavelet variance, 6, 12, and 35 years periods were detected within 50-year scale, and the 35-year period is the most significant one. Similar analyses were conducted for the sunspot relative number during the same period of 1919–2008. The sunspot series showed an 11-year periodic variation, and two energy center. Then, the correlation analyses for 11-year scale were computed. From a long-term period (1919–2008) view, there is no significant correlation between the sediment discharge and the sunspot relative number; however, it is evident that the correlations exist in short-term periods. The results also indicate that the relationships between solar activities and the erosion of the Loess Plateau are complicated.