Evaluation of the Miklip Decadal Prediction System Using Satellite Based Cloud Products
Abstract:The decadal hindcast simulations performed for the “Mittelfristige Klimaprognosen” (MiKlip, decadal climate predictions) project are evaluated using satellite-retrieved cloud parameters from the CM SAF cLoud, Albedo and RAdiation dataset from AVHRR data (CLARA-A1) provided by the Satellite Application Facility on Climate Monitoring (CM SAF) and from the International Cloud Climatology Project (ISCCP). The forecast quality of two sets of hindcasts, Baseline-1-LR and Baseline-0, which use different ocean anomaly initializations, is assessed. While Baseline-0 uses an ocean only initialization, Baseline-1-LR additionally uses full field initialization of atmospheric fields.
Basic evaluation focuses on multi-year ensemble mean fields and cloud-type histograms utilizing satellite simulator output. Additionally, ensemble evaluation employing analysis of variance (ANOVA), analysis rank histograms (ARH) and a deterministic correlation score is performed. Satellite simulator output is available for a subset of the full hindcast ensembles only. Therefore, the raw model cloud cover is additionally used. The Baseline-1-LR hindcasts are closer to satellite data with respect to the simulated tropical/subtropical mean cloud cover pattern than the reference hindcasts (Baseline-0) emphasizing improvements of the initialisation procedure used for Baseline-1-LR when compared to Baseline-0. A slightly overestimated occurrence rate of optically thick cloud-types is analyzed for different experiments including hindcasts and simulations using realistic sea surface boundaries according to the Atmospheric Model Intercomparison Project. By contrast, the evaluation of cirrus and cirrostratus clouds is complicated by observational based uncertainties. Ensemble evaluation of the Baseline-1-LR hindcasts reveals potential predictability of the 2-5 lead year averaged total cloud cover for a large part of the tropical warm pool (TWP) region when regarding the full observational period. However, the hindcasts show only moderate positive correlations with the CLARA-A1 satellite retrieval for the TWP region which are hardly statistical significant. Evidence for predictability of the 2-5 lead year averaged total cloud cover is found for parts of the equatorial to mid-latitudinal North Atlantic.