Simulations of the tropical intraseasonal oscillation by the atmospheric general circulation model of the beijing climate center

The performance of BCC (Beijing Climate Center) AGCM 2.0.1 (Atmospheric General Circulation Model version 2.0.1) in simulating the tropical intraseasonal oscillation (TIO) is examined in this paper. The simulations are validated against observation and compared with the NCAR CAM3 (Community Atmosphere Model version 3) results. The BCC AGCM2.0.1 is developed based on the original BCC AGCM (version 1) and NCAR CAM3. New reference atmosphere and reference pressure are introduced into the model. Therefore, the original prognostic variables of temperature and surface pressure become their departures from the reference atmosphere. A new Zhang-McFarlane convective parameterization scheme is incorporated into the model with a few modifications. Other modifications include those in the boundary layer process and snow cover calculation. All simulations are run for 52 yr from 1949 to 2001 under the lower boundary conditions of observed monthly SST. The TIOs from the model are analyzed. The comparison shows that the NCAR CAM3 has a poor ability in simulating the TIO. The simulated strength of the TIO is very weak. The energy of the eastward moving waves is similar to that of the westward moving waves in CAM3. While in observation the former is much larger than the latter. The seasonal variation and spatial distribution of the TIO produced by CAM3 are also much different from the observation. The ability of the BCC AGCM2.0.1 in simulating the TIO is significantly better. The simulated TIO is evident. The strength of the TIO produced by the BCC AGCM2.0.1 is close to the observation. The energy of eastward moving waves is much stronger than that of the westward moving waves, which is consistent with the observation. There is no significant difference in the seasonal variation and spatial distribution of the TIO between the BCC model simulation and the observation. In general, the BCC model performs better than CAM3 in simulating the TIO.