North Pacific - North American Circulation and Precipitation Anomalies Associated With the Madden-Julian Oscillation

摘要

The Madden-Julian Oscillation (MJO) has been associated with extreme precipitation events in western North America. However, the mechanisms for, and predictability of these associations are not clear. We have examined the influence of the MJO on North Pacific - North America (NPNA) circulation and precipitation anomalies. We constructed composites of MJO events determined from the Wheeler RMM1/RMM2 index of MJO activity. Our analyses were based on NCEP reanalysis data. We focused our investigations on the impacts on NPNA circulation and precipitation of: (1) the location and amplitude of the MJO; (2) the season of MJO occurrence; and (3) concurrent El Ni o (EN) or La Ni a (LN) events. We found that the NPNA response to MJO activity is sensitive to the location of both the convective and subsidence components of the MJO, the season of MJO occurrence, and the existence of concurrent EN or LN events. EN or LN events affect the extratropical response to the MJO by altering the equatorial Rossby-Kelvin wave response to the MJO. This affects the anomalous extratropical wave trains initiated by the MJO, and alters the resulting NPNA precipitation anomalies. Our results provide a foundation for improving extended range forecasts of NPNA circulation and precipitation.