Improved MJO Forecasts Using the Experimental Global‐Nested GFDL SHiELD Model. Issue 6 (14th March 2023) - Zavadoff, Breanna L.
Abstract: Sitting at the crossroads of weather and climate, the Madden‐Julian Oscillation (MJO) is considered a primary source of subseasonal predictability. Despite its importance, numerical models struggle with MJO prediction as its convection moves through the complex Maritime Continent (MC) environment. Motivated by the ongoing effort to improve MJO prediction, we use the System for High‐resolution prediction on Earth‐to‐Local Domains (SHiELD) model to run two sets of forecasts, one with and one without a nested grid over the MC. By efficiently leveraging high‐resolution grid spacing, the nested grid reduces amplitude and phase errors and extends the model's predictive skill by about 10 days. These enhancements are tied to improvements in predicted zonal wind from the Indian Ocean to the Pacific, facilitated by westerly wind bias reduction in the nested grid. Results from this study suggest that minimizing circulation biases over the MC can lead to substantial advancements in skillful MJO prediction. Plain Language Summary: The Madden‐Julian Oscillation, a large‐scale system that moves west to east from the Indian Ocean to the Pacific Ocean over the course of 2–3 months, exerts significant influence on atmospheric circulation worldwide. Nestled somewhere between near‐term weather and long‐term climate, accurate prediction of the Madden‐Julian Oscillation can be used to extend forecasts into the subseasonal, or 3–4 weeks range. In this study the global‐scale System for High‐resolution prediction on Earth‐to‐Local Domains model is used to run two sets of forecasts, one with and one without an advanced grid integrated into the global model over and around Indonesia. This region, known as the Maritime Continent, is a troublesome area for Madden‐Julian Oscillation prediction in numerical models due to its complex environment, which makes it a prime target for the advanced grid. Integrating the advanced grid into the forecasts is shown to extend the skill of Madden‐Julian Oscillation predictions by about 10 days and improve their accuracy. These enhancements are tied to a better representation of the wind field in the advanced grid area, which suggests that substantial advancements in predicting the Madden‐Julian Oscillation can be made by simply minimizing circulation biases over the Maritime Continent in numerical models. Key Points: Integrating a nested grid over the Maritime Continent (MC) in SHiELD extends Madden‐Julian Oscillation (MJO) prediction skill by about 10 days with enhanced reliability Positive impacts imparted by the two‐way nested grid on the MJO extend beyond the confines of the nested region An improved representation of the mean circulation over the MC in the nested grid contributes to substantial advancements in MJO prediction