WP 5 - Intercomparing reanalysis results


The objective of this workpackage is to "propose a process to compare the results of different reanalysis techniques". The formulation of these processes will be split into three tasks:

Task 5.1 Survey uncertainties in re-analysis products

Under this taks an analysis will be made of the requirements of the scientific community on the transparency of reanalyses and uncertainties addressed by the scientific community. This work will be carried out by planning and implementing a targeted web portal enquiry (deliverable D5.1) that will be linked to the CORE-CLIMAX webpage and distributed to weather data re-analysis users and developers benefitting from the RIO webportal http://reanalyses.org/. The proposed enquiry will survey the awareness of the scientific community on targeted uncertainties in the reanalyses, and the effects of these to deliver climate services. Global datasets of ~20-30 years exist for several of the Essential Climate variables (ECVs) at a spatial resolution of the order of 50-100 km; regional or national datasets exist also, at higher resolution, and recent efforts have been put into regional reanalyses for high latitudes. An important aspect that affects the quality of these datasets are the input observations: different temporal resolution, inconsistencies in accuracies between sensors, data gaps and lack of proper merging of data from different sensors into credible CDRs. The survey will also collect targeted information on requirements from the scientific community regarding the improvement of reanalyses for better climate services. For example, one current known limitation of global reanalyses is the representation of the global water cycle; does that point to needed improvements of CDRs and, if so, which ones? Proceeding by ECV, this is the sort of question this task will ultimately try to answer.

Task 5.2 Collecting and synthesizing information from global and regional reanalyses

Here we will focus on the process of building a database of diagnostics for reanalyses to allow quantitative comparison between reanalyses, as well as between reanalyses and CDR and other COPERNICUS -observations.

The following actions will be formalized in this task.

  1. Reanalysis gridded fields and observation feedback (when available) need to be acquired, re-formatted and archived in a petabyte-scale database with state-of-the-art exploration, data mining, and visualization tools.
  2. A database of the statistic diagnostics of time-series, monthly maps, climate indices computed from the reanalysis fields, and fundamental budget residuals statistics need to be derived. The list of diagnostics to be elaborated will build on those already developed by the DWD Regional Climate Centre on Climate Monitoring (RCC-CM), KNMI’s (Royal Dutch Meteorological Institute) Climate Explorer, and ECMWF Reanalysis Climate Monitoring. So-called ‘forward operators’ are becoming increasingly popular for model validation as they allow to fully exploit the information provided by satellite sensor (instead of using a derived product, the model is used to simulate the satellite observation which is then compared to the observed one). Such an approach is currently applied in the German Reanalysis Project and could also be of interest for the intercomparison of different reanalysis techniques. Within the Cloud Feedback Model Intercomparison Project (CFMIP), a flexible tool for the integration of such simulator into a variety of climate models has been developed (COSP). An intercomparison of reanalyses would also benefit from the availability of such tools.
  3. A merged database that enables instant access to time-series of major metrics of assimilation need to be derived for CDRs and all assimilated observations. This will allow direct comparison of metrics for CDR and other COPERNICUS -observations, as well as comparison between reanalyses.
  4. Feeding from the databases above, differences between CDR fit to reanalysis will need to be surveyed. These differences (especially in trends) point to yet-to-be-understood sources of error in the models or the CDRs. Analysis of fits to other observations, such as in situ physical measurements going back several decades, bring additional information to answer these questions.

Overall, this task will produce a formal process allowing to highlight systematic differences between reanalyses, as well as between reanalyses and CDRs.

Task 5.3 Targeted survey of reanalysis product limitations and possible impacts to climate services

Here we will summarize the findings of Tasks 5.1 and 5.2 highlighting the uncertainties and gaps that need addressing to deliver climate services.

More specifically this task will also coordinate closely with other reanalysis initiatives and projects and identify differences in gridded information in the interactions and exchanges between the domains atmosphere, ocean and land. In contrast to WP3 (Task 3.2) which emphasizes on the validation of the consistency of gridded information, this task focuses on the uncertainties and gaps that need addressing to deliver climate services.

This task will synthesize the whole work package WP5. It will be of importance for the COPERNICUS -climate future and climate services on national and global scales.