The Madden-Julian Oscillation in NCEP Coupled Model Simulation

This study doc u ments a de tailed anal y sis on the Mad den-Julian Os cil la tion (MJO) sim u lated by the Na tional Cen ters for En vi ron men tal Pre dic tion (NCEP) us ing the Global Fore cast Sys tem (GFS) model ver sion 2003 cou pled with the Cli mate Fore cast Sys tem model (CFS) con sist ing of the 2003 ver sion of GFS and the Geo phys i cal Fluid Dy nam ics Lab o ra tory (GFDL) Mod u lar Ocean Model V.3 (MOM3). The anal y ses are based upon a 21-year sim u la tion of AMIP-type with GFS and CMIP-type with CFS. It is found that air-sea cou pling in CFS is shown to im prove the co her ence be tween con vec tion and large-scale cir cu la tion as so ci ated with the MJO. The too fast prop a ga tion of con vec tion from the In dian Ocean to the mar i time con ti nents and the west ern Pa cific in GFS is im proved (slowed down) in CFS. Both GFS and CFS pro duce too strong intraseasonal con vec tive heat ing and cir cu la tion anom a lies in the cen tral-east ern Pa cific; fur ther, the air-sea cou pling in CFS en hances this un re al is tic fea ture. The sim u lated mean slow phase speed of east ward prop a gat ing low-wavenumber com po nents shown in the wavenumber-fre quency spec tra is due to the slow prop a ga tion in the cen tral-east ern Pa cific in both GFS and CFS. Er rors in model cli ma tol ogy may have some ef fect upon the sim u lated MJO and two pos si ble in flu ences are: (i) CFS fails to sim u late the wes ter lies over mar i time con ti nents and west ern Pa cific ar eas, re sult ing in an un re al is tic rep re sen ta tion of sur face la tent heat flux as so ci ated with the MJO; and (ii) ver ti cal east erly wind shear from the In dian Ocean to the west ern Pacific in CFS is much weaker than that in the observation and in GFS, which may adversely affect the eastward propagation of the simulated MJO.