Influences of the Madden Julian Oscillations on Temperature and Precipitation in North America during ENSO-Neutral and Weak ENSO Winters

1. Introduction A number of studies have shown that the Madden-Julian Oscillation (MJO) have a strong influence on the atmospheric circulation and precipitation patterns in the Recent studies also suggest that the MJO-related tropical forcing is linked to precipitation events along the west coast of the United State during the winter season (Mo and Higgins 1998; Higgins et al. 2000). Dynamical models generally simulate the MJO quite poorly, partly because of inherent difficulties in parameterizing tropical convection. Statistical prediction models have shown a modest skill relating subseasonal variations in tropical convection to week-2 prediction of wintertime rainfall in western North America (Whitaker and Weickmann 2001). Operational week two ensemble predictions show levels of skill that are comparable to the statistical forecasts. However, neither statistical or dynamical prediction models have demonstrated useful levels of skill in forecasting MJO-related impacts beyond week 2. We believe that improved monitoring and assessment of the MJO and its impacts on the atmospheric circulation and precipitation patterns will lead to better prediction. In this work we focus on ENSO-neutral and weak ENSO winters since the MJO is known to be quite active during those times. Velocity potential at 200-hPa has been used to construct a composite index for life cycles of the MJO (Knutson and Weickmann 1987). A similar approach is taken here. An extended Empirical Orthogonal Function (EEOF) analysis is applied to the bandpass filtered (25-87 days) pentad velocity potential at 200-hPa for ENSO-neutral and weak ENSO winters (November-April) during 1979-2000. The first EEOF is composed of ten time-lagged patterns. We construct ten