Abstract
Efficiency of ensemble experiment is examined for the purpose of describing the time development of tropical atmospheric response to a sea surface temperature (SST) anomaly. An ensemble experiment with the test cases of 200 is carried out by the use of a simplified atmospheric general circulation model (AGCM). The surface boundary condition is idealized to have a local warm SST area placed on the equator of a sphere covered with an SST distribution symmetric around the equator and zonally uniform (“aqua-planet”).
It is shown that the ensemble mean operation effectively reduce the small-scale random noise caused by precipitation activity and the noise known as intraseasonal oscillation. It is demonstrated that the time-development of planetary scale responce to the warm SST area can be clearly extracted by the enesemble mean operation. It is found that the ensemble size of at least 64 is required to extract the time-development of pressure field.
