Description: Dusty cirrus clouds are extended optically thick cirrocumulus decks that occur during strong mineral dust events. So far, they have been mostly documented over Europe associated with dust-infused baroclinic storms. Since today's global operational numerical weather prediction models neither predict mineral dust distributions nor consider the interaction of dust with cloud microphysics, they cannot simulate this phenomenon. We have performed ICON-ART limited-area simulations with 2 km grid spacing to understand and predict the formation of dusty cirrus clouds. Based on these simulations, we postulate that the dusty cirrus forms through a mixing instability of moist clean air with drier dusty air. A corresponding sub-grid parameterization is suggested and tested in the ICON-ART model. Only with help of this special sub-grid parameterization ICON-ART is able to simulate the formation of the dusty cirrus, which leads to substantial improvements in cloud cover and radiative fluxes compared to simulations without this parameterization. A statistical evaluation over six Saharan dust events with and without observed dusty cirrus shows robust improvements in cloud and radiation scores. The ability to simulate dusty cirrus formation removes the linear dependency on mineral dust aerosol optical depth from the bias of the radiative fluxes. This suggests that the formation of dusty cirrus clouds is the dominant aerosol-cloud-radiation effect of mineral dust over Europe. At the IUGG we will present first simulations with the dusty cirrus parameterization in the global ICON-ART model and discuss the occurrence of dusty cirrus in Asia.

Description: For efficient planning and integration of photovoltaic power plants into the power grids, better knowledge of the aerosol-cloud-radiation interaction and more accurate radiation forecasts are needed. However, most operational numerical weather prediction models rely on an aerosol climatology and ignore the spatio-temporal variability of the atmospheric aerosol. In special weather conditions like Saharan dust outbreaks or extended wildfires, this leads to significant deficiencies in the operational forecasts. At Deutscher Wetter­dienst (DWD) and Karlsruhe Institute of Technology (KIT) the project "PermaStrom" aims to improve radiation forecasts. Using the ICON-ART modeling system the emission, transport, and deposition of mineral dust, black carbon from vegetation fires, and sea salt are explicitly simulated. To achieve the project goals and to examine in detail, the effect of Saharan dust on solar radiation, accurate and extensive measurements of the Saharan dust in the atmosphere and of the ground reaching solar radiation is needed. In our presentation, we will show results for several strong dust episodes in Germany. Dust clouds transported from the Saharan region to Germany are detected and tracked using ceilometer, spectroscopic and broadband radiation measurements from several sites within the measurement network of the DWD. We will focus on the direct and indirect aerosol effects and how these affect the solar irradiance at the ground. Furthermore, we will show how the implementation of prognostic mineral dust in the ICON-ART NWP model can improve the radiation forecasts during such events.

Description: We study long-term changes in surface radiative fluxes and their causes using surface radiation observations from the German Weather Service.Time series of solar radiation observations initiated at Potsdam in 1937 demonstrate the decrease in global radiation from the 1950s caused by an increase in the atmospheric aerosol load due to anthropogenic activities. This dimming period is followed by a brightening from the middle of the 1980s, i.e. an increase in global radiation caused by a decrease in the aerosol load as a consequence of the implementation of mechanism of air poullution reduction. The decrease in the Aerosol Optical Depth (AOD) is well documented by sunphotometer observations, which were initiated in the mid-eighties.While the aerosol load has stabilized at low levels after the turn of the century and thus the direct aerosol effect has decreased, the global radiation continues to increase. It is likely that other atmospheric phenomena such as cloudiness contribute to the recent increase in global radiation and hence in the incoming radiative energy as the incoming longwave radiation has been also increasing, mainly due to raising air temperature and greenhouse gas concentrations, which is in line with the output of GCM’s. We study changes in cloudiness using the concept of the cloud radiative effect (CRE). Preliminary results indicate that the magnitude of the CRE has decreased which implies a decrease in cloud cover, shift towards a different cloud type and/or changes in microphysical cloud properties.