Convectively Coupled Equatorial Wave Simulations Using the ECMWF IFS and the NOAA GFS Cumulus Convection Schemes in the NOAA GFS Model

Abstract

There is a longstanding challenge in numerical weather and climate prediction to accurately model tropical wave variability, including convectively coupled equatorial waves (CCEWs) and the Madden–Julian oscillation. For subseasonal prediction, the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS) has been shown to be superior to the NOAA Global Forecast System (GFS) in simulating tropical variability, suggesting that the ECMWF model is better at simulating the interaction between cumulus convection and the large-scale tropical circulation. In this study, we experiment with the cumulus convection scheme of the ECMWF IFS in a research version of the GFS to understand which aspects of the IFS cumulus convection scheme outperform those of the GFS convection scheme in the tropics. We show that the IFS cumulus convection scheme produces significantly different tropical moisture and temperature tendency profiles from those simulated by the GFS convection scheme when it is coupled with other physics schemes in the GFS physics package. We show that a consistent treatment of the interaction between parameterized convective plumes in the GFS planetary boundary layer (PBL) and the IFS convection scheme is required for the GFS to replicate the tropical temperature and moisture profiles simulated by the IFS model. The GFS model with the IFS convection scheme, and the consistent treatment between the convection and PBL schemes, produces much more organized convection in the tropics, and generates tropical waves that propagate more coherently than the GFS in its default configuration due to better simulated interaction between low-level convergence and precipitation.

Atmospheric tropical modes are important drivers of Sahelian springtime heatwaves

“…Besides, with the amelioration of weather observation networks, the increase of computational capacity and improvement of numerical models, tropical modes are now better represented and predicted (Dias et al 2018;Janiga et al 2018;Kim et al 2018;Bengtsson et al 2019). These skills can therefore be transferred to heatwave prediction at the intraseasonal scale and thus help to win time for preparedness actions.…”

“…The reason for the focus on tropical modes is the potential for predictability at intraseasonal lead times. Tropical modes are indeed good sources of predictability at these scales (Moron et al 2018b;Dias et al 2018;Bengtsson et al 2019;Li and Stechmann 2020;Judt 2020).…”

Skill of Global Raw and Postprocessed Ensemble Predictions of Rainfall in the Tropics

“…The coupling relies on a wave-induced modification of environmental conditions for convection such as convergence, stability, moisture availability, and shear (Schlueter et al 2019a,b). Although a relatively high level of intrinsic predictability has recently been shown for equatorial waves (Li and Stechmann 2020;Judt 2020), NWP models are known to lose wave energy too quickly and to misrepresent propagation, partly due to precipitation being triggered too easily by convective parameterization schemes (Lin et al 2008;Frierson et al 2011;Dias et al 2018;Bengtsson et al 2019).…”

Prediction skill of Sahelian heatwaves out to subseasonal lead times and importance of atmospheric tropical modes of variability

“…The main reason for this preference is that in most inter-model comparative studies, ECMWF has proved to be the most skilful (e.g. Janiga et al 2018;de Andrade et al 2019;Bengtsson et al 2019). In addition, national meteorological services in the Sahel can freely access some of the ECMWF high-resolution real-time forecast data (including 2 m temperature), thanks to a partnership between the African Centre for Meteorological Applications for Development (ACMAD) and the European Centre.…”