Fanglin Yang1, Lisa Bengtsson2, Ligia Bernardet3 on behalf of the UFS physics
developers.
Editor: Krishna Kumar4
1 NOAA NCEP EMC, 2 NOAA ESRL PSL, 3 NOAA GSL, 4 EPIC
Improving forecasts of extreme weather, such as heavy precipitation, severe storms, heatwaves, and other
impactful weather, across various temporal/spatial scales, is of utmost importance for NOAA. Under the Unified
Forecast System’s Research to Operations Project, the development of NOAA’s next generation fully coupled global
Earth System models includes innovations in physics, dynamics, coupling, and initial condition generation, which
have been included in so-called “coupled prototypes” within the UFS in a stepwise manner. The Global Forecast System
(GFSv17) and its ensemble counterpart, the Global Ensemble Forecast System (GEFSv13) will be the first coupled
global applications to become operational under the Unified Forecast System infrastructure. For atmospheric physics,
incremental changes were introduced to the model physics during the prototype phases spanning from GFSv16 physics
suite to the forthcoming GFSv17/GEFSv13 physics suite. GFSv17 is targeted for medium-range weather forecasts at 9-km
horizontal grid-spacing. GEFSv13 is targeted for sub-seasonal forecasts at 25-km resolution. The model physics
developed for GFSv17/GEFSv13 is also the starting point for the atmospheric component of the UFS Seasonal Forecast
System (SFSv1), which will run for seasonal lead times at 50-km resolution.
The Unified Forecast System – Research to Operations (UFS-R2O) Project is a major ongoing undertaking at the NOAA’s Office of Science and Technology Integration in the National Weather Service (NWS), in collaboration with the Weather Program Office in the Office of Oceanic and Atmospheric Research (OAR). Within this project research scientists from the NOAA Environmental Modeling Center (EMC) and Research Laboratories – Physical Sciences Laboratory (PSL) and Global Systems Laboratory (GSL), in collaboration with the wider NWP community, undertook a unified physics parameterization approach under the UFS infrastructure performing multiple updates in many prototype versions, targeting the next upgrade of the operational systems. Importantly, all the new innovations, improvements and refinements have been carefully tested and integrated into a well tuned suite over several years of development (2020 to present). The updates have led to significant improvements in reduction of known biases and enhanced forecast skill (Figure 1)
Fig 1. Comparison of Northern Hemisphere 500-hPa Height Anomaly Correlations:This analysis compares the Northern Hemisphere 500-hPa height anomaly correlations in the winter of 2019/20 between the current operational model (GFSv16 at a 13-km grid resolution) and two experimental versions of GFSv17 (HR3b and HR4 at a 9-km grid resolution). GFSv16 is an atmospheric model initialized through data assimilation, while the experimental GFSv17 is a fully coupled atmos-ocean-ice-wave model initialized using replay initial conditions. All models were verified against the ECMWF IFS analysis. Hollow bars in the lower panel indicate differences between GFSv17 and GFSv16 that are statistically significant at the 95% level based on the Student’s t-test. (Plot produced by Lydia Stefanova, EMC).
Among the several physics updates for use in more than one UFS Application are: (i) introduction of improved cumulus convection parameterizations innovations (Bengtsson and Han, 2024), such as stochasticity, 3-dimensional sub-grid organizational effects, and a new prognostic closure to predict the evolution of convective clouds. These innovations improved tropical variability and tropical temperature/humidity biases leading to improvements in the prediction of the Madden Julian Oscillation (MJO), see summary in Fig 2 below, and Bengtsson et al. 2022. The updates to cumulus convection were also shown to improve forecasts of Convective Available Potential Energy (CAPE) forecasts as well as precipitation over the Contiguous United States (CONUS). (ii) A two-moment cloud microphysics scheme (Thompson et al. 2004) was introduced as a new scheme to unify development between global and regional applications. In the global applications the scheme improves the representation of super-cooled liquid clouds, radiative fluxes, cloud cover and precipitation. Additional developments of semi-Lagrangian sedimentation and inner-loop time-stepping was developed on top of the Thompson microphysics scheme to address challenges related to numerical stability when running the scheme with large time-steps (based on Juang and Hong, 2010). (iii) Improvements in Rapid Radiative Transfer Model for GCMs (RRTMG) radiation includes introduction of a new Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA2) climatology (Cheng and Yang, 2023), and refinements to address excessive large net short wave (SW) net to ocean at low sun angles. (iv) Improvements in surface layer, and planetary boundary layer schemes were introduced to address known biases in the stably stratified atmosphere and hurricane prediction (Han et al. 2024). (v) Introduction of a new land surface model (Noah-MP, Niu, G.-Y., et al. 2011) has helped address known GFSv16 biases in 2-m temperature, humidity and CAPE forecasts, (vi) advances to orographic and non-orographic Gravity Wave Drag (GWD), small-scale GWD and adding turbulence orographic form drag for improved atmospheric circulation, (vii) implementing aerosol-radiation and aerosol-cloud interactions using either the prescribed MERRA2 aerosol climatology or prognostic Goddard Chemistry Aerosol Radiation & Transport Model (GOCART) aerosols, (viii) introduction of fractional grid compositing albedo and emissivity for coupling stability and consistency along the coast lines and (ix) introduction of a positive-definite tracer transport scheme applied to the PBL and convection parameterizations (Yang et al. 2009, Bengtsson and Han, 2024). These physics innovations, along with infrastructure development to allow for coupling to a dynamic ocean (MOM6), sea ice (CICE6), and waves (WW3) have led to significant improvements in the latest prototypes of GFSv17/GEFSv13 compared to the atmosphere only current operational models.
Another goal for the UFS-R2O physics development team has been to unify physics across scales to the extent possible to accelerate the Research to Operations (R2O) transition of physics innovations maintaining operational efficiency. With this in mind, several physics updates were also incorporated in the regional applications such as HAFS v1 and v2 (5.4/1.8 km), RRFSv1 (3-km) and AQMv7 (12 km). All innovations have been incorporated into the CCPP public code repository on GitHub, with a subset of them being supported to the community via the CCPP v7 public release issued in September 2024.
Acknowledgements:
UFS physics development is a community effort, primarily funded by NWS OSTI
and OAR WPO, through institutional base funds, and various initiatives, including UFS-R2O, JTTI, DRSA and IRA
projects etc.
References:
Bengtsson,
L., L. Gerard, J. Han, M. Gehne, W. Li, and J. Dias, 2022: A Prognostic-Stochastic and Scale-Adaptive Cumulus
Convection Closure for Improved Tropical Variability and Convective Gray-Zone Representation in NOAA’s Unified
Forecast System (UFS). Mon. Wea. Rev., 150, 3211–3227, https://doi.org/10.1175/MWR-D-22-0114.1.
Bengtsson, L., and J. Han, 2024: Updates to NOAA’s Unified Forecast System’s cumulus convection parameterization scheme between GFSv16 and GFSv17. Wea. Forecasting, 39, no. 11. https://doi.org/10.1175/WAF-D-23-0232.1.
Cheng, A., and F. Yang, 2023: Direct Radiative Effects of Aerosols on Numerical Weather Forecasts—A Comparison of Two Aerosol Datasets in the NCEP GFS. Wea. Forecasting, 38, 753–772, https://doi.org/10.1175/WAF-D-22-0060.1.
Han, J., J. Peng, W. Li, W. Wang, Z. Zhang, F. Yang, and W. Zheng, 2024: Updates in the NCEP GFS PBL and Convection Models with Environmental Wind Shear Effect and Modified Entrainment and Detrainment Rates and Their Impacts on the GFS Hurricane and CAPE Forecasts. Wea. Forecasting, 39, 679–688, https://doi.org/10.1175/WAF-D-23-0134.1.
Henry Juang, H., and S. Hong, 2010: Forward Semi-Lagrangian Advection with Mass Conservation and Positive Definiteness for Falling Hydrometeors. Mon. Wea. Rev., 138, 1778–1791, https://doi.org/10.1175/2009MWR3109.1.
Niu, G.-Y., et al. (2011), The community Noah land surface model with multiparameterization options (Noah-MP): 1. Model description and evaluation with local-scale measurements, J. Geophys. Res., 116, D12109, doi:10.1029/2010JD015139.
Thompson, G., R. M. Rasmussen, and K. Manning, 2004: Explicit Forecasts of Winter Precipitation Using an Improved Bulk Microphysics Scheme. Part I: Description and Sensitivity Analysis. Mon. Wea. Rev., 132, 519–542, https://doi.org/10.1175/1520-0493(2004)132<0519:EFOWPU>2.0.CO;2.
Yang, F., S. Moorthi, M. Iredell, H. Juang, S. Lord, J. Sela, R. Treadon, J. Jung, and H.-L. Pan, 2009: On the negative water vapor in the NCEP GFS. Sources and Solutions. 23rd Conference in Weather Analysis and Forecasting/19th Conference on Numerical Weather Prediction, Omaha, NE.
