From Descriptive Records to Instrumental Measurements: Addressing Inhomogeneities in the 250-Year Fog Time Series of Padua

The fog in Padua, Italy, is the result of a complex interplay between local climate, pol-lution and synoptic-scale meteorological conditions. The modern definition of “fog” was adopted by the World Meteorological Organization, founded in 1950. Prior to that, no precise visibility threshold had been established, and early meteorological observers recorded its occurrence based on subjective criteria. The meteorological observations made in Padua since the mid-18th century include sky conditions and fog, but the dis-tinction between fog and mist was undefined, making it difficult to compare records from different observers. Caution is therefore needed when analyzing fog occurrence to distinguish the climate signal from observational artifacts. For instance, at the Specola Observatory in Padua from 1773 to 1913, the fog that appeared only on the horizon—but not at the zenith—was often disregarded, since vertical visibility was crucial for astronomical observations. Starting from 1920, other manned stations be-gan providing systematic fog records, which have continued to the present. The aim of this study is to reconstruct the occurrence of fog in Padua since the late 18th century. As available datasets —observational and instrumental—partly overlap in time, and data from nearby locations are available, it is possible to assess their mutual con-sistency, to evaluate the reliability of historical visual observations, and to investigate fog variability and trend over time.