Heat budget analysis in three typical warm periods simulated by FGOALS-s2

Abstract

This study compared basic warming patterns among three typical warm periods — the mid-Holocene (MH), Medieval Warm Period (MWP), and the twentieth century warming (20CW) — and carried out a comprehensive heat budget analysis using four experiments simulated by the Flexible Global Ocean–Atmosphere–Land System model, Spectral Version 2 (FGOALS-s2). The model simulates similar spatial warming patterns in all three warm periods, e.g. stronger warming appears in the high latitudes. However, changes in surface air temperature (SAT) over the tropical regions are different: a significant warming occurs in the 20CW and MWP but a significant cooling in the MH. The heat budget analysis suggested that SAT changes are mainly induced by the heat flux. In the MH, the insolation and positive snow and ice feedback are responsible for the warming in the Southern Ocean but the wind anomalies and decreased downward longwave radiation (DLR) induce the cooling in the tropics. In the 20CW, the decreased shortwave radiation and increased sea surface temperature dependency of evaporation dampen the warming in the tropics. In the MWP, the shortwave radiation induces the Southern Ocean warming, but the DLR and wind anomalies warm the SAT in the tropics. The simulated ocean temperature and ocean heat content anomalies are different in the upper ocean (above 1500 m), which are mainly induced by the wind stress changes, but similar in the deep ocean in all three warm periods.