ERA-CLIM: Historical Surface and Upper-Air Data for Future Reanalyses

Future reanalyses might profit from assimilating additional historical surface as well as upper-air data. In the framework of the European Reanalysis of Global Climate Observations (ERACLIM; www.era-clim.eu) project, significant amounts of pre-1957 upper-air and surface data have been cataloged (>2.5 million station days), imaged (>450,000 images), and digitized (>1.25 million station days) to prepare new input datasets for upcoming reanalyses. These data cover large parts of the globe, focusing henceforth on less well-covered regions such as the tropics, the polar regions, and the oceans and on very early twentieth-century upper-air data from Europe and the United States. The total numbers of digitized/inventoried records (i.e., time series of meteorological data at fixed stations or from moving observational platforms) are 80/214 (surface), 735/1,783 (upper air), and 61/101 [moving upper-air (i.e., data from ships, etc.)]. Here, the authors give an overview of the data rescue activities, the data, and the applied quality checking procedures and demonstrate their usefulness for analyzing past weather and climate. The data will be made available online (at www.era-clim.eu). The upper-air data will be included in the next version of the Comprehensive Historical Upper-Air Network (CHUAN) and are also available online (http://doi.pangaea.de/10.1594/PANGAEA.821222).