Nonlinear atmospheric variability in the winter northeast Pacific associated with the Madden-Julian oscillation

Abstract

The Madden-Julian Oscillation (MJO), the primary mode of large-scale intraseasonal variability in the tropics, is known to relate to the mid-latitude atmospheric variability. Using neural network techniques, a nonlinear projection of the MJO onto the precipitation and 200-hPa wind anomalies in the northeast Pacific during January-March shows asymmetric atmospheric patterns associated with different phases of the MJO. For precipitation, the strength of the nonlinear effect to the linear effect was 0.94 (in terms of the squared anomalies and averaged over all phases of the MJO), indicating strong nonlinearity, while for the 200-hPa wind, the ratio was 0.55, indicating moderate nonlinearity. In general, anomalous winds blowing from the north or from land were associated with negative precipitation anomalies, while winds from the south or from the open ocean, with positive precipitation anomalies. The nonlinear effects generally induced positive precipitation anomalies during all phases of the MJO. Copyright 2005 by the American Geophysical Union.