Science
The main goal auf the Research Unit C3SAR is to better understand the role of 3d cloud variability. Furthermore, we want to provide robust tools in cloud remote sensing and cloud radiative forcing parameterization that account for 3d radiative effects in a feasible and realistic manner. Thereby, we will combine the research expertise on cloud resolving atmospheric and radiative transfer modelling as well as ground- and satellite based remote sensing and radiative flux observations. This cooperative approach can provide the required data, methodologies and tools to realistically account for 3d radiation transports. Thus, C3SAR will, for the first time, allow us to correct biases in climate modelling and cloud remote sensing, that have been a result from oversimplifications of the complex geometrical nature of clouds.
To do this, the team will use typical 3D cloud shapes from detailed cloud modelling and synergistic satellite observations. These shapes will be used in radiative transfer models of different complexity to quantify the consequences of cloud structure simplifications and to establish physically based cloud-radiation correlations. Long-term, high-quality ground-based observations of clouds and radiation provide the validation of these relations by means of radiative closure studies. Both current and new generations of satellite sensors will provide the corresponding closure at the top of the atmosphere.
The scientific work in the C3SAR Research Unit is organized in five projects with contributions from five partner institutions. The scientific work is led by nine principal investigators (PIs). The table below lists the C3SAR-projects as well as the the involved institutions and PIs.
| Project | Project Leader | Institution | Research Area |
|---|---|---|---|
| P1: Modelling cloud micro – and macrophysical properties and their radiative effect | Vera Schemann, Fabian Senf | Uni Cologne, Tropos | Cloud resolving modeling, 3d radiative transfer |
| P2: Cloud structure and regime dependencies of 3D radiative effects | Hartwig Deneke, Bernhard Mayer | Tropos, LMU | Cloud remote sensing, 3d radiative transfer |
| P3: Cloud radiative effects from ground-based vertically resolved cloud & radiation observations & radition closure | Christine Knist, Stefan Wacker, Gunther Seckmayer | DWD, Uni Hanover | Cloud remote sensing and radiation observations |
| P4: Satellite-based cloud remote sensing & 3d effects | Anja Hünerbein, Martin Stengel | Tropos, DWD | Cloud remote sensing |
| P5: 3D field campaigns: HOPE + Lindenberg 2026 | Andreas Macke, Gunther Seckmeyer, Stefan Wacker | Tropos, Uni Hanover, DWD | Cloud and radiation field observation and modeling |
| P6: Coordination | Andreas Macke | Tropos |
The subsequent figure displays a scheme about the five scientific projects of C3SAR and their interplay.
Project 1 provides high spatiotemporal and microphysically resolved cloud fields from state-of-the-art cloud resolved modelling. This will provide the data base to understand the variability of cloud properties relevant for radiative transfer and remote sensing. The modelling results will cover specific cloud regimes and cloud scenarios that have been extensively observed during recent field campaigns. Modelling results around field observations will bring the latter into a more complete context. The resulting cloud fields will be used for a variety of radiative transfer sensitivity studies with different degrees of complexity. These studies will systematically evaluate the role of cloud spatial and microphysical variability on transmitted and reflected radiative fluxes (for climate applications) and radiances (for remote sensing applications) and thus provide the basis for cloud-regime-resolved cloud-radiation correlations.
Project 2 extends and critically evaluates the analyses of Project 1 to different cloud regimes by means of statistical cloud reconstructions and 3d radiative transfer. Cloud reconstructions will be performed by combining vertically resolved cloud properties from active space-borne sensors with horizontally resolved cloud properties from passive imagers. Thanks to the vast amount of available satellite data, regime-dependent 3D cloud properties can be obtained. These can be used to construct realistic and climatologically representative input cloud scenes as an input to the 3D radiative transfer model MYSTIC. Thus, we will obtain empirical regime-resolved relationships between clouds and radiation. These relationships are applicable to both climate modelling and global remote sensing.
In Project 3, an empirical cloud-radiation correlation is established, that is based on long term vertically resolved cloud and radiation measurements at the Lindenberg Observatory of the DWD. In addition, in-situ measured broadband and spectral irradiance will be used for radiation closure. Thanks to the availability of long-term observations at Lindenberg, statistically robust cloud-radiation correlation can be inferred and compared to those from a modelling perspective in Project 1 and a satellite perspective in Project 2. In addition, these measurements are extended during a three-month measurement-campaign in Lindenberg in summer 2026. There, also the spectral radiance will be measured by the advanced multidirectional spectroradiometer AMUDIS, which was developed in Hannover.
Based on improved cloud-radiance correlations as achieved in the Projects 1, 2 and 3, Project 4 will revisit satellite-based cloud remote sensing with account for 3d effects in calculating cloud and irradiance products. Project 4 will establish new proxies for cloud inhomogeneity for different cloud regimes. Inhomogeneity corrections of satellite-based cloud and radiation products will be applied.
Project P5 is based on long-term observations in Lindenberg in combination with the field campaign at the Lindenberg Observatory. At the C3SAR-field-campaign, the suite of available instruments at the observatory will be expanded by measurements of spectral radiance, performed with AMUDIS. Furthermore, a network of pyranometers will be deployed. These ground-based measurements are combined with satellite-based observations and models to obtain the most complete set of co-located data sets on cloud and radiation properties. This will allow to test the cloud-radiation-dependency developed by this research unit. Project 5 will also contain data from new satellite sensors on Board MTG and EarthCARE that will obtain the physical and radiation properties of clouds from space.
In the envisaged second phase, the research unit will expand this approach to more testbeds around the world through large international observation networks. It will improve the regime-based cloud-radiation relations and apply those to climate modelling and the new generations of satellite sensors.