Regional-scale surface air temperature and East Asian summer monsoon changes during the last millennium simulated by the FGOALS-gl climate system model

Abstract

The spatial patterns and regional-scale surface air temperature (SAT) changes during the last millennium, as well as the variability of the East Asian summer monsoon (EASM) were simulated with a low-resolution version of Flexible Global Ocean-Atmosphere-Land-Sea-ice (FGOALS-gl) model. The model was driven by both natural and anthropogenic forcing agents. Major features of the simulated past millennial Northern Hemisphere (NH) mean SAT variations, including the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA) and the 20th Century Warming (20CW), were generally consistent with the reconstructions. The simulated MCA showed a global cooling pattern with reference to the 1961–90 mean conditions, indicating the 20CW to be unprecedented over the last millennium in the simulation. The LIA was characterized by pronounced coldness over the continental extratropical NH in both the reconstruction and the simulation. The simulated global mean SAT difference between the MCA and LIA was 0.14°C, with enhanced warming over high-latitude NH continental regions. Consistencies between the simulation and the reconstruction on regional scales were lower than those on hemispheric scales. The major features agreed well between the simulated and reconstructed SAT variations over the Chinese domain, despite some inconsistency in details among different reconstructions. The EASM circulation during the MCA was stronger than that during the LIA The corresponding rainfall anomalies exhibited excessive rainfall in the north but deficient rainfall in the south. Both the zonal and meridional thermal contrast were enhanced during the MCA. This temperature anomaly pattern favored a stronger monsoon circulation.