An 11-Year Analysis of Daily Homogenitus Cloud Observations in the NE Iberian Peninsula (2015–2025)

In 2014, the Meteorological Service of Catalonia established systematic daily observations of anthropogenic clouds, defined in 2017 by08 the WMO as homogenitus. This initiative aimed to quantify the human contribution to cloud cover through direct observation. Since 2015, a comprehensive database of daily observations has been maintained at La Selva del Camp observatory (Spain). Using this 11-year dataset, two distinct analyses were performed. First, a statistical analysis focused on both high homogenitus clouds (contrails) from aircraft and low homogenitus clouds from a nearby chemical complex. To uncover the underlying periodicities of these phenomena, a Fast Fourier Transform (FFT) was applied to the monthly time series, revealing a dominant 12-month seasonal cycle alongside a significant long-term increasing trend. This analysis quantified average cloud cover and identified seasonal and annual trends spanning daily to interannual scales. Furthermore, the environmental impact of these persistent tracks was evaluated through a radiative forcing assessment, weighing the cooling albedo effect against longwave terrestrial radiation trapping. Second, the study examines ‘peak events’ where contrail coverage exceeded 2 and 3 oktas. Ultimately, this work connects multi-year visual observations with mathematical frequency spectra and energy budget assessments, providing a robust framework to evaluate the local climatic and radiative footprint of persistent anthropogenic cloudiness.