The THORPEX observation impact Inter-comparison experiment
Despite differences in the assimilation algorithms and forecast models, the impacts of the major observation types are similar in each forecast system in a global sense. However, regional details and other aspects of the results can differ substantially. Large forecast error reductions are provided by satellite radiances, geostationary satellite winds, radiosondes and commercial aircraft. Other observation types provide smaller impacts individually, but their combined impact is significant. In all systems, only a small majority (less than 55%) of the total number of observations assimilated actually improves the forecast, and most of the overall improvement comes from a large number of observations that have relatively small individual impacts. Both results point to the advantage of increasing the number of observations assimilated as opposed to seeking a more limited set that produces only the largest impacts, and to the potential importance of having some level of redundancy between observing systems. Accounting for this behavior may also be important when considering strategies for deploying adaptive (or ``targeted") components of the observing system.