The Madden-Julian Oscillation and Its Impact on Northern Hemisphere Weather Predictability

摘要

The Madden-Julian oscillation (MJO) is known as the dominant mode of tropical intraseasonal variability and has an important role in the coupled-atmosphere system. This study uses numerical model experiments to investigate the influence of the MJO activity on weather predictability in the midlatitudes of the Northern Hemisphere. The National Aeronautics and Space Administration (NASA) Goddard Laboratory for the Atmospheres (GLA) general circulation model was used in a 10-yr simulation with fixed climatological SSTs to generate a control dataset as well as to select initial conditions for active MJO periods and "Null" cases. Two perturbation numerical experiments were performed for the 75 cases selected [(4 MJO phases + Null phase) X 15 initial conditions in each]. For each alternative initial condition, the model was integrated for 90 days. Mean anomaly correlations and standardized root-mean-square errors in the midlatitudes of the Northern Hemisphere (20°-60°N) were computed to assess predictability characteristics. The analyses of 500-hPa geopotential height, 200-hPa streamfunction, and 850-hPa zonal wind component systematically show larger predictability (～2-3 days) during periods of active MJO as opposed to quiescent episodes of the oscillation. While further studies are necessary to investigate possible model sensitivity, the results shown here highlight the importance of the MJO in modulating weather variability and show the importance of improving the representation of the MJO in operational numerical weather forecast models.