Simulated analysis of summer climate on centennial time scale in eastern China during the last millennium

Abstract

Using Lanczos filtered simulation results from the ECHO-G coupled ocean-atmosphere model, this study analyzes the spatiotemporal structure of temperature and precipitation on centennial time scale to examine how climate change in eastern China responded to external forcing during the last millennium. The conclusions are (1) eastern China experienced a warm-cold-warm climate transition, and the transition from the warm period to the cold period was slower than the cold to warm transition which followed it. There was more rainfall in the warm periods, and the transitional peak and valley of precipitation lag those of temperature. The effective solar radiation and solar irradiance have significant impacts on the temporal variation of both temperature and precipitation. Volcanic activity plays an important role in the sudden drop of temperature before the Present Warm Period (PWP). There is a positive correlation between precipitation and volcanic activity before 1400 A.D., and a negative relationship between the two thereafter. The concentration of greenhouse gases increases in the PWP, and the temperature and precipitation increase accordingly. (2) The spatial pattern of the first leading empirical orthogonal function (EOF) mode of temperature on centennial time scale is consistent with that on the inter-annual/inter-decadal (IA-ID) time scales; namely, the entirety of eastern China is of the same sign. This pattern has good coherence with effective solar radiation and the concentrations of greenhouse gases. The first leading EOF mode of precipitation on centennial time scale is totally different from that on the IA-ID time scales. The first leading mode of centennial time scale changes consistently over the entirety of eastern China, while the middle and lower reaches of the Yangtze and Yellow Rivers are the opposite to the rest of eastern China is the leading spatial pattern on IA-ID time scale. The distribution of precipitation on centennial time scale is affected by solar irradiance and greenhouse gas concentrations.