Impact of a New Radiation Package, McRad, in the ECMWF Integrated Forecasting System

Abstract

A new radiation package, "McRad," has become operational with cycle 32R2 of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). McRad includes an improved description of the land surface albedo from Moderate Resolution Imaging Spectroradiometer (MODIS) observations, the Monte Carlo independent column approximation treatment of the radiative transfer in clouds, and the Rapid Radiative Transfer Model shortwave scheme. The impact of McRad on year-long simulations at T L 159L91 and higher-resolution 10-day forecasts is then documented.McRad is shown to benefit the representation of most parameters over both shorter and longer time scales, relative to the previous operational version of the radiative transfer schemes. At all resolutions, McRad improves the representation of the cloud-radiation interactions, particularly in the tropical regions, with improved temperature and wind objective scores through a reduction of some systematic errors in the position of tropical convection as a result of a change in the overall distribution of diabatic heating over the vertical plane, inducing a geographical redistribution of the centers of convection. Although smaller, the improvement is also seen in the rmse of geopotential in the Northern and Southern Hemispheres and over Europe. Given the importance of cloudiness in modulating the radiative fluxes, the sensitivity of the model to cloud overlap assumption (COA) is also addressed, with emphasis on the flexibility that is inherent to this new RT approach when dealing with COA. The sensitivity of the forecasts to the space interpolation that is required to efficiently address the high computational cost of the RT parameterization is also revisited. A reduction of the radiation grid for the Ensemble Prediction System is shown to be of little impact on the scores while reducing the computational cost of the radiation computations. McRad is also shown to decrease the cold bias in ocean surface temperature in climate integrations with a coupled ocean system.

Benefits of explicit urban parameterization in regional climate modeling to study climate and city interactions

“…In particular, it includes a new turbulence scheme with a 1.5-order prognostic scheme for the turbulence kinetic energy (Cuxart et al 2000); a new convection scheme including dry, shallow, and deep convection (Piriou et al 2007;Guérémy 2011); a new large-scale microphysics scheme with prognostic liquid/ solid cloud/rain variables based on the work of Lopez (2002) and a new radiative scheme for infrared radiation (RRTM, Rapid Radiative Transfer Model, Mlawer et al 1997). An updated version (6 bands) of the shortwave radiation scheme is used (Fouquart and Bonnel 1980;Morcrette et al 2008). Similarly to the version 5, the mixing length is nonlocal and based on Bougeault and Lacarrere (1989) and the PDF-based cloud scheme is based on Ricard and Royer (1993).…”

Evaluation of NWP results for wintertime nocturnal boundary‐layer temperatures over Europe and Finland

“…In addition, HIRLAM includes an ice tile and AROME a town tile. The radiation schemes applied in the four models vary from a simple, fast scheme (Savijärvi, 1990) applied in HIRLAM to the sophisticated RRTM scheme with the Monte Carlo Independent Column Approximation approach (Morcrette et al, 2008a) for cloud-radiation interactions, applied in IFS. The condensation schemes in IFS, HIRLAM and GFS are based on Sundqvist (1978), whereas AROME employs a subgrid scheme for warmphase and ice-phase clouds.…”

Dynamical kernel of the Aladin–NH spectral limited‐area model: Revised formulation and sensitivity experiments

“…It includes the long-wave radiation transfer scheme RRTM (Mlawer et al, 1997;Morcrette et al, 2001) and a short-wave radiation scheme with six spectral intervals (Fouquart and Bonnel, 1980;Morcrette, 1993). A maximum-random-overlap assumption is used and the cloud fraction and cloud optical thickness are two separate quantities.…”