To better understand variability in weather and climate, it is vital to address past atmospheric circulation. This need requires meteorological information not just from the surface but also at upper levels. Current global upper-level datasets only reach back to the 1940s or 1950s and do not cover some important periods in the first half of the twentieth century. Extending the observational record is therefore considered important in order to analyze climate variability in the past and verify global climate models used to predict future climate change. Although earlier upper-air data from platforms such as radiosondes, aircraft, pilot balloons, registering balloons, and kites are available from various sources, no systematic compilation and quality assessment of upper-level data prior to the International Geophysical Year (1957/58) has ever been performed. Here we present the Comprehensive Historical Upper-Air Network (CHUAN). It is a consistent global historical upper-air dataset that has been derived from heterogeneous data available from various sources as well as from newly digitized data. This paper describes the CHUAN dataset, the metadata, the quality control procedures, and the relationship to existing datasets. Some examples are given of its usefulness for analyzing weather and climate during the first half of the twentieth century. The CHUAN dataset comprises 3987 station records worldwide or about 16.4 million profiles (of which 12.6 million are before 1958 and 5.3 million, primarily from pilot balloons, are before 1948). A monthly mean version can be downloaded from the World Wide Web (

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Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland

NOAA National Climatic Data Center, Asheville, North Carolina

National Center for Atmospheric Research, Boulder, Colorado

Météo-France, Toulouse, France

Finnish Meteorological Institute, Helsinki, Finland

Deutscher Wetterdienst, Meteorological Observatory, Lindenberg, Germany

MeteoSwiss Aerological Station, Payerne, Switzerland

Arctic and Antarctic Research Institute, St. Petersburg, Russia

RIHMI-WDC, Obninsk, Russia

Met Office Hadley Centre, Exeter, United Kingdom

University of Colorado CIRES Climate Diagnostics Center, and NOAA Earth System Research Laboratory/Physical Sciences Division, Boulder, Colorado