Diverse Mechanism of the Tibetan Plateau Effect on the North Atlantic Deep Water Formation on Seasonal Timescale

SHAO Xing1, YANG Haijun2,†

1. Laboratory for Climate and Ocean-atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871; 2. Department of Atmospheric and Oceanic Sciences, Fudan University, Shanghai 200438; † Corresponding author, E-mail: yanghj@fudan.edu.cn

Abstract Using the fully coupled model CESM1.0, the seasonal difference of the Tibetan Plateau (TP) effect on the North Atlantic deep water (NADW) formation mechanism is investigated qualitatively by comparing the sensitivity test without the TP and the control test with realistic topography. The result shows that the TP effect on the mechanism of the NADW formation varies with the seasons. The NADW formation decreases when the TP is removed, the significant increase of net surface heat flux in cold season (October to March of two consecutive years in the Northern Hemisphere) dominates the prominent decrease of the NADW formation, however, the significant increase of freshwater flux due to the mass of sea ice melting leads to the remarkable decrease of the NADW formation in warm season (April to September of the same year). The TP has a more significant effect on the NADW formation in the low resolution coupled model. The main difference of the TP effect on the NADW formation mechanism in different seasons is that the presence of TP topography increases the sea surface heat loss of the NADW formation region in cold season, also leads to decrease of the freshwater input from the northern sea ice in warm season. Key words Tibetan Plateau; North Atlantic deep water (NADW) formation; seasonal timescale; freshwater flux; heat flux