1. 1 Topical Group ”Cloud Mask” - Outcome of presentations and discussions Karl-Göran Karlsson SMHI, Norrköping Sweden Presentation at ICWG workshop Lille, France 18 May 2016

2. 2 Content: 1.Wednesday morning (before coffee break): Block of presentations - Validation of cloud mask (Karl-Göran Karlsson) - Various cloud detection problems (Adam Dybbroe, Timo Hanschmann, Marie Doutriaux-Boucher) - New cloud detection approaches (Andrew Heidinger, Byung-il Lee, Johan Strandgren) 2.Wednesday morning (after coffee break): Two other TG sessions (Climate products + Retrieval of uncertainties) 3.Wednesday afternoon (after coffee break): ”Cloud Mask” discussions! 4.Friday morning: Concluding discussions

3. 3 Some common ”Cloud Mask”/”Climate” recommendations 1.The current GEWEX cloud database should be maintained and extended with new datasets. On a longer term, a revision (e.g. higher resolution) should be considered. 2.Active sensor data (CALIPSO/CLOUDSAT + EarthCARE) are invaluable and indispensable for the cloud retrieval community. Post-EarthCARE successors must urgently be identified and planned for. 3.Long-term AVHRR calibration issues (both IR and VIS) still need to be resolved. SCOPE-CM ”AVHRR GAC FCDR” activity (SCM-05) should be strengthened and/or extended.

4. 4 Discussion on possible ”Cloud Mask”-only recommendations 1.Can we recommend an optimal CALIPSO-CALIOP cloud mask validation strategy (namely the combined use of cloud optical depth filtered 1km/5km data)? Or do we need further studies on combining 330m/5km data and use of CALIOP version 4 data? 2.Can we recommend further and extended use of global CALIPSO-derived cloud mask performance maps? 3.How do we analyse the global performance of data from morning orbit satellites (only high-lat CALIOP matches)? Use SEVIRI or other geo cloud masks at low/mid latitudes?

5. 5 Discussion on possible ”Cloud Mask”-only recommendations 4.Any future for ground-based cloud observations for validation (SYNOP, WSI, cloud radars, cloud lidars, etc.) 5.Any recommendation on use of new features for cloud masking or sea-ice detection (11-8.6 micron, 1.3 micron) in operational and climate applications? 6.Improving cirrus detection: Best way forward regarding additional use of sounding channels? Additional skills from ANN approaches? 7.Is there a need for BUFR-format cloud products for NWP? Complementary or not to COSP simulators?

6. 6 Discussion on possible ”Cloud Mask”-only recommendations 7.Are there particular recommendations for geo cloud masking? Inter-comparisons should be done between full multispectral masks (new but not applicable on historic data) and bi-spectral masks (old but climate relevant)? 8.Polar night cloud masking: Do we have to live with permanent cloud/clear non-separability (additional sounding channels cannot solve all problems)? 9.Probabilistic cloud masking: The obvious way to go or…? How can we otherwise get cloud mask uncertainties? But what is our truth when training?

7. 7 Discussion on possible ”Cloud Mask”-only recommendations 10.Futuristic view: When do we get cloud/aerosol/ccn- resolving models backing up OE retrievals?