Monday, 12 January 2009: 2:00 PM
Extended-Range Predictions of Madden-Julian Oscillations with the Goddard Multi-scale Modeling System
Room 129A (Phoenix Convention Center)
It is well known that accurate prediction of tropical activity at sub-seasonal scales (~30 days) is crucial for extending the predictability of numerical weather prediction (NWP) beyond two weeks. Among the challenges in predicting tropical activity is the accurate forecasting of an MJO (Madden and Julian 1972, 1994), which is one of the most prominent large-scale features of the tropical general circulation with a 45-60 day time scale. It is typically characterized by deep convection originating over the Indian Ocean and subsequent eastward propagation into the Pacific Ocean. Current understanding (including theory and hypotheses) indicates that (1) moisture convergence (e.g., Lau and Peng 1987; Wang 1988), (2) surface heat and moisture fluxes (e.g., Emanuel 1987; Neelin et al. 1987), (3) cloud-radiation feedback (e.g., Hu and Randall 1994, 1995), (4) convection-water vapor feedback (e.g., Woolnough et al. 2000; Tompkins 2001), and (5) “discharge-recharge” associated with moist static energy build-up and release (e.g., Blade and Hartmann 1993) are important for the MJO's initiation, intensification, and propagation (see a review by Zhang 2005).
By taking advantage of existing global and cloud models, the so-called multi-scale modeling framework (MMF, e.g., Khairoutdinov and Randall, 2003; Tao et al., 2008) provides an innovative approach for understanding these multiple processes and multi-scale interactions. While the MMF approach has shown promising long-term simulations, its performance on short-term and/or extended range simulations is less understood. Compared to climate simulation, which is viewed as a boundary value problem, short-term weather simulation/forecasting is an initial-value problem. Therefore, it is argued that accurate sub-seasonal forecasts may depend on the accurate representation of both initial and boundary conditions, suggesting the importance of model initialization. In this case study, we will address the Goddard MMF's suitability for short-term and extended-range weather forecasts, which are aimed at improving the model's ability to simulate sub-seasonal weather systems.