Analysis of the 10-years daily observation of homogenitus clouds in Catalonia (2014-2024).

In 2014 the Catalan Weather Service started in some of the weather observatories in Catalonia the systematic daily observation of clouds caused by human activities (Mazon et al., 2012), the homogenitus clouds defined by the WMO in 2017 (https://cloudatlas.wmo.int/en/homogenitus.html ). It was a pioneer initiative that aimed to account by direct observations the contribution of human activities to the cloud cover. After 10 years of systematic observations, a daily homogenitus clouds observation database has been built in one of these observation locations, la Selva del Camp observatory (located near 100 km south to Barcelona city). By using this datase, two analysis have been performed. The first one has been a statistical analysis, focused on the high homogenitus clouds, caused by aircrafts. The analysis has been done at different temporal scale, from daily, to annual and interannual, which allows us to quantify the average percentage of cloud cover by high clouds produced by aircrafts (contrails), and the annual and seasonal trend within this period. The second analysis focusses on those days with contrails covering more than 2 and 3 octas. A synoptic and temperature analysis has been done at sea level, 850 and 500 hPa of geopotential height during the previous days and the day of the peak of the anthropic clouds, which allows to stablish the relationship between extreme events of high anthropic clouds and geopotential height at 850 and 500 hPa.     Mazón, J., Costa, M., Pino, D. and Lorente, J. (2012), Clouds caused by human activities. Weather, 67: 302-306. https://doi.org/10.1002/wea.1949