Day-to-day temperature variability trends in 160- to 275-year-long European instrumental records

Day-to-day temperature variability is investigated in eight European series of daily mean temperatures beginning between 1722 and 1833. Eight statistical measures of day-to-day temperature variability are compared. The intramonthly standard deviation of daily temperature anomalies is found to be a good measure. The absolute change in temperature anomaly from one day to the next is sensitive to changes in observational procedures and is suggested as a diagnostic tool for identification of inhomogeneities in instrumental temperature series. Because many changes in observational procedures have taken place, quantitative estimates of trends in day-to-day variability, based on all series, could only be calculated for 1880-1998. A trend analysis over this period indicates an increase by 5% in southwest Europe, 0 to -5% change in the northwest, and a decrease by 5 to 10% in northeast Europe. On a longer time perspective, day-to-day temperature variability in winter, spring, and autumn in northern Europe has decreased over the last 200-250 years. The frequency of extremely cold winter days in northern Europe was lower in the twentieth century than in the eighteenth and nineteenth centuries. Day-to-day temperature variability in winter in northern Europe was negatively correlated with a North Atlantic Oscillation index in the period 1826-1997, but some other factor must also have contributed to the long-term variability decrease. More long daily temperature series, and development of homogenization methods for such data, are needed for an improved knowledge of long-term changes in day-to-day temperature variability.