Historical fog climate dataset for Carpathian Basin from 1886 to 1919.

This paper presents the historical fog climate dataset from 1886 to 1919 for Hungary and its neighbouring countries in the Carpathian Basin. The dataset was obtained from the yearbooks of the Royal Hungarian Central Institute of Meteorology and Earth Magnetism (RHCIMEM) established in 1870 to investigate the climatic features of Hungary during the time of the Austro-Hungarian Monarchy. Monthly observations were recorded from 1871 and daily observations were recorded from 1886. The yearbooks contain daily meteorological records of temperature, relative humidity, rainfall, pressure, wind speed and direction, cloudiness and surface weather conditions along with monthly summaries for 24 meteorological stations. The daily weather observations were recorded three times a day, namely at 07:00, 14:00 and 21:00 local time. Station information (location, environment, instrumentation, observations etc.) can also be found in the yearbooks as metadata. For example, the definition of fog in the case of historical observations is the same as that of today, i.e., fog is detected if the maximum horizontal visibility is less than 1 km. In this way fog observations are easily comparable to today's observations without requiring further data correction and homogenisation. The longest 13 continuously recorded fog observation datasets have the length between 15 and 34 years. The stations are located in 5 countries of the Carpathian Basin at present. These datastests are suitable for conducting historical climatic investigations and can also serve as reference datasets. The historical dataset can be used to study the annual and seasonal changes in frequency and duration of fog events in the Carpathian Basin as a reference, thus facilitating research in the field of fog climatology and forecast.