Seasonal Evolution of the Subtropical Anticyclones Simulated in FGOALS-s2

Abstract

Here, the simulation characteristics of the seasonal evolution of the subtropical anticyclones (SAs) in the Northern Hemisphere are documented using the Spectral version 2 of the Flexible Global Ocean–Atmosphere–Land System Model (FGOALS-s2) developed at LASG/IAP. We also address the understanding of the seasonal evolution of these SAs. Compared to the ERA-40 global reanalysis data, the general features of the SAs and their evolution were well simulated in both winter and summer, although a pronounced bias was found in the generation of the South Asia Anticyclone (SAA) in spring. It is found that condensation heating plays a dominant role in the seasonal development of the SAA and the Subtropical Anticyclone over the Western Pacific (SAWP) in the middle troposphere. The condensation heating biases in the model account for the biases of the establishment of the SAA in spring and the weaker strength of the SAA and the SAWP from spring to summer. Moreover, an overestimation of condensation heating was found to persist in the east-central tropical Pacific from winter to summer, with an underestimation found above the area from the South China Sea to the western Pacific from spring to summer. Such biases can generate an illusive anticyclonic gyre in the upper troposphere above the middle Pacific and delay the generation of the SAA over South Asia in April. Conversely, the two surface SAs in the eastern oceans during spring to summer were found to be controlled primarily by the surface sensible heating over the Eurasian and North American continents in the Northern Hemisphere; these anticyclones were simulated reasonably well, although their centers have been shifted westward relative to the observations owing to weaker longwave radiation cooling in the simulation, which was likely associated with much weaker local stratiform cloud. Further improvements in the parameterizations of physical processes are identified.