Data rescue of historical wind observations in Sweden since the 1920s

Abstract. Instrumental measurements of wind speed and direction from the 1920s to the 1940s from 13 stations in Sweden have been rescued and digitized, making 165 additional station years of wind data available through the Swedish Meteorological and Hydrological Institute’s open data portal. These stations measured wind through different versions of cup-type anemometers and were mainly situated at lighthouses along the coasts and at airports. The work followed the protocol "Guidelines on Best Practices for Climate Data Rescue" of the World Meteorological Organization consisting of (i) designing a template for digitization; (ii) digitizing records in paper journals by a scanner; (iii) typing numbers of wind speed and direction data into the template and (iv) performing quality control of the raw observation data. Along with the digitization of the wind observations, meta data from the stations were collected and compiled as support to the following quality control and homogenization of the wind data. The meta data mainly consist of changes in observer and a small number of changes in instrument types and positions. The rescue of these early wind observations can help improve our understanding of long-term wind changes and multidecadal variability (e.g., the "stilling" vs. "reversal" phenomena), but also to evaluate and assess climate simulations of the past. Digitized data can be accessed through the SMHI open data portal: https://www.smhi.se/data, last access: 26 December 2022, and Zenodo repository: https://doi.org/10.5281/zenodo.5850264, last access: 26 December 2022, (Zhou et al., 2022).