Long‐term variability of the low‐level cloud base height in Poland

The aim of the study is to characterize long-term variability low-level cloud base heights (CBH) in Poland years 1971–2020. Data were used from six weather stations belonging Institute Meteorology and Water Management – National Research (IMWM-NRI), where CBH was first measured using IWO device and, since 1990s, a ceilometer. analysis allowed for data eight observation periods (0000, 0300, 0600, 0900, 1200, 1500, 1800, 2100 UTC), which referred several height ranges (between ground surface 2500 m a.s.l.). In analysed multiyear period, cool half year, Cumulonimbus bases increased significantly, that is, number cases at >1000 warm >1500 m. recent years, Cumulus with between 300 999 has clearly decreased, while it 1000–1499 (in October–March) 1500–1999 (April–September). A similar increase found case Stratocumulus (their greater share 1500 2499 m). It only Stratus lowering noticed, possibly owing imperfect measurement fractus species. positive upward trend most clouds can be explained by statistically significant temperature decrease relative air humidity lower troposphere.