Climate Series

The three long temperature series from Armagh, namely the maximum and minimum temperatures (1843-present), the twice-daily outside temperatures (1795-1882) and the twice-daily dry-bulb temperatures (1844-1965) have been recalibrated and averaged to form a single long temperature series from 1796 to 2003. A gap of nine years, from 1825-1833, was largely filled by data from the Dunsink Observatory (DIAS) and the Phoenix Park (Dublin), leaving only a few months in the 208 years duration of the series with no data. There is a good correspondence between the three series for years in common.

**Figure 3:** Annual mean temperatures at Armagh Observatory from three independently calibrated series. Mean values of the maximum and minimum temperatures (1843-present) are shown in black; the means of the twice-daily outside temperatures (1795-1882) are shown in blue; and the means of the twice-daily dry-bulb temperatures (1844-1965) are shown in red. The upper part of the figure illustrates the linkage between the data points shown in the lower part.
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The results indicate that there were two periods in the 19th century lasting a decade or more when annual mean temperatures in Armagh were similar to those in the mid-to-late 20th century. Comparison with temperature series from other sites in NW Europe shows that similar conditions prevailed elsewhere in Europe. It is suggested that the choice of the late 19th century as the base line for 20th century global warming may be misleading as temperatures at this time were abnormally low.

The data also show a gradual reduction in the daily temperature range over the period since 1844 which may be connected with the increasing trend in cloudiness in Ireland mentioned in previous annual reports.

In addition, the soil temperatures recorded at Armagh from 1904 at depths of one foot (subsequently 30cm) and four feet (subsequently 1 metre) have been calibrated with corrections applied for the change from imperial to metric units and for changes in the location of the instruments. Comparison with data from two other sites in Ireland, namely Birr and Valentia, shows consistent trends at all three sites. Although there has been a general upward trend in soil temperatures over the 20th century, the trend does not closely follow air temperature.

Other series that have been recently standardised include the humidity series from 1838 and the pressure series from 1795. The latter will, with similar data from other sites in the UK and Europe, help to establish the phase of the North Atlantic Oscillation back to the late 18th century.

The standardization of the various Armagh Meteorological Series has resulted in a higher profile for the Observatory's long involvement in climate monitoring. As a result, several studies of long time series from Europe and the UK now include data from Armagh Observatory.