Modeling the East Asian Climate During the Late Cretaceous (80 Ma)

In this study, the East Asian climate during the Late Cretaceous (ca 80 Ma) is examined by using the Community Climate System Model Version 2 (CCSM2) from the National Center for Atmospheric Research (NCAR) and the reconstructed palaeogeographic data. The simulation results indicate that the large-scale prevailing wind directions and pressure systems over East Asia showed a remarkable seasonal variation during 80 Ma, so that it can be inferred that there existed a monsoon circulation over East Asia at that time. Compared to the present climate, the atmospheric circulation systems over the Eurasian continent in the Late Cretaceous showed a stronger meridional feature, which was possibly correspondent to a smaller lateral extension of the Eurasian continent at that time. Moreover, under a warmer background in the Late Cretaceous, the winter and summer monsoons over East Asia showed a synchronous variation, with a stronger winter monsoon as well as a stronger summer monsoon. The pattern of annual mean precipitation was similar to that of the present climate, with the maximum precipitation appearing in the intertropical convergence zone (ITCZ) between 10°S and 10°N. There was also more precipitation over the eastern coasts of the continent adjacent to the western Pacific, with the central value exceeding 1200 mm, and there was less precipitation in the midlatitudes of the inland areas. Although a more precipitation belt also appeared near 30°N over the western Pacific, which was similar to the present climate, there was no high precipitation belt over the land of East Asia. This feature implies that the uplift of the Tibetan Plateau plays an important role in the formation of the present baiu (plum rains). Moreover, the simulated climate over East Asia during 80 Ma was warmer relative to the present and the surface air temperature was 2 °C higher at the same latitudes compared to the present climate. This simulation result is closer to the estimation from the geological evidences.