The earliest daily barometric pressure readings in Italy: Pisa ad 1657-1658 and Modena ad 1694, and the weather over Europe

The earliest daily barometric pressure readings were taken during the Maunder Minimum of Solar activity (1645-1715). In Italy, observations were made at Pisa over the years 1657-1658 by V. Viviani and A. Borelli, and at Modena during the year 1694 by B. Ramazzini. These readings have been recovered, corrected and adjusted to modern units. The early instruments used and their problems have been thoroughly discussed. Barometer observations recorded by John Locke in Essex (UK) during the year 1694 have also been recovered and corrected. Daily observations were recorded during the same period in Paris by L. Morin; these have previously been published by Legrand and Le Goff ( 1992: Les observations meteorologiques de Louis Morin. Monographie No. 6, Direction de la Meteorologie Nationale, Ministere de l'Equipement, de Logement et des Transports, 41 pp.). However, cross-comparisons with the Locke and Ramazzini data have shown that the Paris series needed a further correction to take into account instrumental error. Using these three corrected series, it has been possible to reconstruct the atmospheric circulation over Europe for the year 1694. An indication of the state of the atmospheric circulation can also be made by using the earlier observations recorded in Italy. A common feature of the two periods studied (1657-1658 and 1694) is that winters were characterized by higher pressure compared with the reference period 1961-1990, while the summers generally experienced lower pressure. This latter conclusion indicates that the Azores High was late or not well developed, favouring low temperature and frequent rain in the late spring and early summer.