A global historical Radiosondes and Tracked Balloons Archive on standard pressure levels back to the 1920s

Abstract

Abstract. Long observed time series of climate state quantities are needed to extend our understanding of global weather, climate variability and monitoring not only at the Earths surface but also the free atmosphere, since climate anomalies and climate change have a three-dimensional spatial structure. Radiosonde data before 1958 and tracked balloon (PILOT) data are rarely available at standard times on standard pressure levels, which complicates their use for climate studies. This paper describes an upper air dataset on standard pressure levels at 00:00 GMT and 12:00 GMT for parameters temperature and wind. The input data sources of this dataset are the Comprehensive Historical Upper Air Network (CHUAN version 1.7), the Integrated Global Radiosonde Archive (IGRA) and upper air observations from the reanalysis datasets ERA-40 and ERA-Interim. As such it contains many data that have been digitized and collected in the EU FP7 project ERA-CLIM. Those data, which partly exist at asynoptic times and on altitude levels instead of pressure levels, have been brought to synoptic times and standard pressure levels using state of the art interpolation techniques, employing geopotential information National Oceanic and Atmosphere Administration (NOAA) 20th Century Reanalysis (NOAA 20CR) to aid the interpolation. The standardized time series have been merged if necessary, taking care that the data are traceable back to their original sources. Only time series longer than 300 days have been saved in the merged archive, since the main purpose of this dataset is to aid climatological studies. If possible WMO numbers have been given to the station records. For some records which have never been identified by a WMO number, a local ID above 100 000 has been attached. This paper describes the merging procedure, data count and data quality and how traceability of the data is ensured. It does not describe a homogenization procedure for both temperature and wind data. Homogeneity adjustments for both temperature and wind will be provided in a forthcoming paper. All the archives and metadata files are available in the PANGAEA archive with associated DOI http://doi.pangaea.de/10.1594/PANGAEA.823617. If users prefer netCDF files, they can be downloaded via http://www.univie.ac.at/theoret-met/research/raobcore/.