The influence of cloud-radiation interaction on the calculation of positive net longwave radiation and temperature in the ICON model under conditions of warm air advection to a snow surface
D.A. Piskunova1, N.E. Chubarova1, M.V. Shatunova1,2, Yu.O. Shuvalova1,2, N.A. Petrov1
1Lomonosov Moscow State University, Moscow, Russia
2Hydrometeorological Centre of Russia, Moscow, Russia
Keywords: longwave radiation, cloud-radiation interaction, three-dimensional effects, ecRAD, ICON, temperature sensitivity
Abstract
To study the influence of three-dimensional cloud effects on the forecast of longwave radiation and air temperature during warm air advection onto a snow surface for the Moscow region, experiments were conducted with the ICON v.2025.04 model using various algorithms of cloud heterogeneity accounting. Additionally, experiments were conducted with the ecRAD radiation scheme in autonomous mode. The ICON model with the McICA algorithm reproduces positive NLR values, but underestimates them. The use of the SPARTACUS algorithm, which makes it possible to describe the three-dimensional effects of clouds, reduced the NLR RMSE by 4 W/m2. At the same time, in the ecRAD autonomous mode, the effects reached 15 W/m2, which corresponded to the measured NLR values within the measurement error. The study showed that the decrease in the effect of the SPARTACUS algorithm in the ICON model is associated with the influence of the algorithm on the cloud properties. Using the ecRAD autonomous mode, nonlinear NLR dependence on the cloud liquid water path and ice water path have been revealed. The temperature sensitivity to NLR changes was 2.7 °C per 100 W/m2 in model experiments with McICA and 4.9 °C per 100 W/m2 in experiments with SPARTACUS for night hours with positive NLR. Differences in the temperature response of the ICON model to changes in longwave radiation due to the replacement of the algorithms are also estimated.
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