Ground-Based Atmospheric Measurements at the Onsala Space Observatory (Sweden): Data & Trends (2009–2025)

Abstract. This study presents a comprehensive long-term dataset of ground-based atmospheric observations collected at the Onsala Space Observatory (OSO), Sweden, between August 2009 and April 2025. The dataset includes measurements of temperature, relative humidity, atmospheric pressure, precipitations, wind speed, gust and direction, and solar irradiance. It offers high-resolution insight into local weather patterns and seasonal variations, making it a valuable resource for climate monitoring and regional environmental studies. Preliminary analysis reveals a warming trend of ∼0.15 °C.yr^-1, with significant seasonal contrasts: the most pronounced increase occurs in winter (203.3 % above the annual trend, so winters are becoming milder), followed by autumn (80.1 %), spring (62.3 %), and summer (32.9 %). Precipitation trends show a significant decrease over the study period. Anomalies such as the particularly cold winters in 2009–2010 and 2010–2011 or the particularly warm winter in 2019–2020 are highlighted and linked with the North Atlantic Oscillation (NAO) phases. This dataset complements existing data for local trend analysis and atmospheric modeling in northern Europe.