TOYODA Eizi (Grad. School of Mathematical Sciences, Univ.
Kensuke NAKAJIMA (Grad. School of Science, Kyushu Univ.)
Masaki ISHIWATARI (Grad. School of Environmental Earth Science, Hokkaido Univ.)
Yoshi-Yuki HAYASHI (Grad. School of Science, Hokkaido Univ.)
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.
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. The required ensemble size for extracting the time-development of pressure field is found to be around 64.
|Received 26 October 1999; accepted 2 November 1999|