2004: The global response to tropical heating in the Madden-Julian Oscillation during Northern winter

• Main Authors: Brian J. Hoskins, Michiko Masutani
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Madden{Julian oscillation Extratropical intraseasonal variability Rossby wave re- sponse Equatorial; Southern Ocean
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.457.8743

A life cycle of the Madden-Julian oscillation (MJO) was constructed, based on 21 years of outgoing longwave radiation data. Regression maps of NCEP-NCAR reanalysis data for northern winter show statistically signicant upper-tropospheric equatorial wave patterns linked to the tropical convection anomalies, and extratropical wave patterns over the North Pacic, North America, the Atlantic, the Southern Ocean and South America. To assess the cause of the circulation anomalies, a global primitive equation model was initialised with the observed three-dimensional winter climatological-mean ow and forced with a time-dependent heat source derived from the observed MJO anomalies. A model MJO cycle was constructed from the global response to the heating, and both the tropical and extratropical circulation anomalies generally matched the observations well. The equatorial wave patterns are estab-lished in a few days, while it takes approximately two weeks for the extratropical patterns to appear. The model response is robust and insensitive to realistic changes in damping and basic state. The model tropical anomalies are consistent with a forced equatorial Rossby{Kelvin wave response to the tropical MJO heating, although it is shifted westward by approximately 20 Æ longitude relative to observations. This may be due to a lack of damping processes (cumulus friction) in the regions of convective heating. Once this shift is accounted for, the extratropical response is consistent with theories of Rossby wave forcing and dispersion on the climatological ow, and the pattern correlation between the observed and modelled extratropical ow is up to 0.85. The observed tropical and extratropical wave patterns accounts for a signicant fraction of the intraseasonal circulation variance, and this reproducibility as a response to tropical MJO convection has implications for global medium-range weather prediction.