Atmospheric radiation in the ICON weather and climate forecast model: current state and development prospects

In the presentation, we discuss the results of studies of the radiative effects of atmospheric aerosol, several greenhouse gases, and clouds obtained in numerical experiments, using Russian ICON-Ru configurations of the non-hydrostatic ICON model, which is applied in short-term numerical weather forecasting within the COSMO-Ru system of the Hydrometeorological Center of Russia. The ICON weather and climate forecast model has recently become one of the most accurate and popular models in the world. As a result, further improvement of the quality of modeling the components of the net radiation in the atmosphere is an urgent task, contributing to the improvement of the forecast of important meteorological characteristics. The calculations were performed using a grid system (including nested grids) with increments from 13 km (for the global configuration) to 1 km.

For clear sky conditions, radiative effects, and anthropogenic radiative heating rate of the most important anthropogenic constituents over the past 20 years were estimated relative to their pre-industrial levels for different seasons of the year on the example of the Moscow region. We analyzed vertical profiles of radiative forcing in the shortwave and longwave spectral ranges and their values at the lower and upper boundaries of the atmosphere, depending on solar angle and surface albedo. The influence of the aerosol vertical structure on radiation is shown in comparison with the measurement data. 

For cloudy conditions, we evaluate the effectiveness of describing the three-dimensional (3D) radiation effects of clouds, when using the SPARTACUS algorithm in the ECRAD autonomous radiation scheme, as well as the account of the additional cloud state. The physical mechanisms of the revealed patterns are discussed. We present the results of modeling solar radiative fluxes in the ICON forecast model using different methods for calculating atmospheric radiation in various cloudy conditions. 

The influence of indirect aerosol effects on cloud cover and their effect on solar radiation is considered. We show that an increase in condensation nuclei in a cloud can lead to a decrease in solar radiation near the Earth's surface by 10-12%. At the same time, the main reason for the discrepancy between measurements and model calculations is an inaccurate description of the spatial structure of clouds and the proportion of direct solar radiation. 

Additionally, the features of reproducing abnormally high values of the long-wave balance and its relationship to the forecast of air temperature at the surface are discussed. The most important factors influencing the formation of this phenomenon are considered.

We also evaluate the influence of radiative effects on the forecast of surface air temperature. We show the estimates of the quality of shortwave and longwave radiation simulations. The causes of uncertainties and the prospects for the development of radiative schemes in the ICON-Ru configurations are discussed. The study was conducted as a part of the research work of Roshydromet, registration number 125032004255-7 and the MSU  research work №121051400081-7.