SIMSAT- simulators of satellite derived cloud datasets for climate models

Satellite product simulators simulate what would be observed by satellite instruments if the underlying atmosphere was that of the model. This allows for a fairer/more useful comparison between models and observations. SMHI is developing two satellite simulators, the EUMETSAT CMSAF simulator and the ESA Cloud_cci simulator.

Climate models are essential for predicting the future climate and associated cloudiness. To add fidelity to climate models, they should show skill in depicting the current cloud climatologies. However, the modelled atmosphere is of necessity strongly parametrised, and modelled clouds only vaguely resemble those retrieved from satellite measurements. On the other hand, retrievals from satellite measurements suffer limitations that models do not. Satellite product simulators exist therefore to simulate what would be observed by satellite instruments, if the underlying atmosphere was that of the model. Thus, such simulators bridge the gap between the modelled and observed world.

The project aim is to develop, test and publish two different simulators for European-based satellite derived cloud datasets. Each will be tested on the EC Earth climate model. The final goal of the project is to have the simulators included in Cloud Feedback Model Intercomparison Project (CFMIP) Observation Simulator Package (COSP). This is mandatory if the satellite datasets are to take part in experiments for the next IPCC report. To be included in COSP, the research using the simulators must be published in peer reviewed articles. Not only is this step vital for the prospects of the proposed satellite product simulators, but also for the individual satellite datasets, if they are to be used internationally by climate modellers for validation.

The suggested research topics include evaluating the sensitivity of model parametrisations and assumptions, evaluating changing cloudiness during the Arctic summer, and investigating the diurnal cycle of clouds over Tropical Africa.

General summary

Tropospheric clouds strongly modulate the incoming and outgoing radiation of the Earth system and are an important component of the water cycle. Depending on a cloud’s properties it may have a warming or cooling effect on the climate (Baran, 2012). Therefore, any climatic changes in cloudiness may have a strong impact on the climate system as a whole. Climate models or Earth system models are essential tools for society for predicting the future climate and associated cloudiness. Therefore, in order to add fidelity to climate models, they should show skill in depicting the current cloud climatologies.

However, the representation of clouds in models is very different from the clouds retrieved from satellite measurements. The modelled atmosphere is of necessity parametrised at the climate model’s resolution, and their clouds are not directly comparable to those retrieved from satellite measurements. On the other hand, retrievals from satellite measurements suffer limitations that models do not, such as wavelength-dependent cloud sensitivity and have limited information of the three dimensional structure of the clouds. Satellite product simulators therefore exist to simulate cloud products that would of been retrieved from satellite measurements, if the underlying atmosphere was that of the model. Therefore, these simulators will help to bridge the gap between the modelled and observed world.

Aim

The project aim is to develop, test and publish two different satellite product simulators. They will simulate three European-based derived cloud datasets. Each will be tested in the climate model EC-Earth. The final goal of the project is to have the simulators included in Cloud Feedback Model Inter-comparison Project (CFMIP) Observation Simulator Package (COSP). This step is vital for the prospects of the proposed satellite simulators, but also to the individual satellite datasets if they are to be used internationally by climate modellers for evaluation and improvements. To reach this goal the simulators must be of high standard and be published in peer-reviewed articles. Specifically, each simulator must add new scientific value to COSP.

The following are the major way-points of the project. Firstly, to continue to develop the three satellite simulators, while continuously assessing the impact of assumptions used in the model and the satellite datasets. Secondly, to perform research using the finished simulators by assessing aspects of cloudiness in EC-Earth. Apart from being a prerequisite for the simulators to be included COSP, publishing these findings will make the simulators internationally recognised. And thirdly, to have the simulators integrated into COSP.

Context of the project

The Swedish Meteorological and Hydrological Institute (SMHI) has heavily invested in this topic since it is a large contributor to the satellite derived datasets we wish to simulate, it is the main developer of the simulators, and it has an important role in the development of the EC-Earth climate model.

The satellite simulators are aimed to help improve the climate models. The climatic spatial distribution and diurnal evolution of clouds will be as- sessed to point out potential problems in the model and suggest improve- ments. Several assumptions used in the model and in the satellite retrievals, will be tested to investigate their impact on the comparisons. The usage of these European based satellite datasets should also increase through the increased visibility gained by demonstrating their usefulness in peer reviewed articles. We consider it very important for the future of the datasets that the satellite simulators may be finished and included in COSP in time to take part in the next IPCC assessment report.

Role of SMHI

SMHI has the sole responsibility for the project.

Collaboration

The project leader is Salomon Eliasson at the Remote sensing unit. Karl Göran Karlsson from the Remote sensing unit and Ulrika Willén from the Rossby center support the project. We are also collaborating with the german and Dutch wether services, DWD and KNMI with these simulators.

Funding and project period

The project is funded by the Swedish national space board and runs from 2015 to 2017.