Simulation of Monsoonal Characteristics of the East Asian Climate during the Mid-Cretaceous in a Coupled Climate Model

Abstract:

To increase understanding of the future changes of the East Asian monsoon (EAM) under the current global warming background, we turn to investigate the EAM during the mid-Cretaceous (~90Ma), which is one of the warmest greenhouse climate episodes of the Phanerozoic. Utilizing the Community Earth System Model (CESM) version 1.03 from the National Center for Atmospheric Research (NCAR), we simulate the global climate in the mid-Cretaceous, and some results can well match with some geological evidences. New indices of monsoon based on the seasonal/annual precipitation ratios are defined, and they can represent modern EAM well. Upon these indices, the simulation results demonstrate that the East Asia has been a typical monsoon region during the mid-Cretaceous, and then the mid-Cretaceous EAM were analyzed and compared with the modern EAM. According to the spatial pattern of the EAM index, the EAM region was divided into two subregions: East Asian low-latitude monsoon (EALM) and East Asian mid-latitude monsoon (EAMM). The mid-Cretaceous EALM was comparable to the modern one, as well as the summer and winter monsoon intensities. However, the monsoon index was reduced obviously in the mid-latitudes of East Asia, which indicates that the mid-Cretaceous EAMM was not as significant as modern. Thorough the analysis on the climatology in the EAMM region, the mid-Cretaceous summer/annual precipitation ratio was smaller than modern, while the winter/annual precipitation ratio was greater. This difference between the mid-Cretaceous and modern EAMM shows that the summer and winter monsoon intensities both weaken and that the uneven distribution of precipitation in different seasons is alleviated in the mid-Cretaceous world, therefore the mid-Cretaceous EAMM is a weaker system.