Modes and mechanisms of sea surface temperature low-frequency variations over the coastal China seas

In this paper, low-frequency variability of annual-mean sea surface temperature in the coastal China seas is studied based on ocean and atmosphere reanalysis products. There are two distinct low-frequency modes: a basin mode and a north-south dipole mode. The former is characterized by a uniform warming over the entire coastal oceans, while the latter is characterized by a seesaw pattern over the shelf seas and the South China Sea. The basin mode is associated with global warming, but it is primarily attributed to oceanic advection, with surface heat flux playing a damping effect due to intensification of the latent heat loss. The dipole mode varies coherently with the Pacific Decadal Oscillation. In contrast to the basin mode, the dipole mode is broadly associated with the surface heat flux, with oceanic advection acting to damp sea surface temperature (SST) in the shelf seas but sustain SST in the South China Sea. A further analysis indicates that the basin mode and the dipole mode derived from the annual-mean SST remain robust in winter and summer, despite some differences in the governing processes. It is found that the summer dipole mode is associated with the Atlantic Multidecadal Oscillation. Therefore, SST over the coastal China seas may be used as a potential indictor of these global-scale climate changes.