Daily Milan temperature and pressure series (1763-1998): history of the observations and data and metadata recovery

Daily meteorological observations have been made at the Brera Astronomical Observatory in Milan since 1763. Initially they concerned air temperature, air pressure, wind direction and state of the sky; other measurements such as precipitation, relative humidity and wind speed were gradually included in the following years. In terms of homogeneity the series can be divided into two main periods, due to the great reorganisation of the observations that Francesco Carlini performed in 1835. As a consequence of other minor changes, each of these periods can then be divided into some other sub-periods, the most problematic years being the first (1763-1804) and the last (1963-today) ones. Within this context the purpose of the paper is to present the history of Milan's temperature and pressure series, giving particular emphasis to all the information that can be useful for the evaluation of the reliability and of the homogeneity of the data. Moreover the data recovery is discussed and the quality and the availability of both hand-written (observatory registers) and published (ephemerides, bulletins, year-books) data and metadata sources are analysed.