Trans-hemispheric effects of large volcanic eruptions as recorded by an early 19th century diary

An early 19th century diary, belonging to a farmer from NW England, contains detailed daily weather entries over a 15-year period from 1815 to 1829. The diary period encompasses the Tambora volcanic eruption and pre-dates the establishment of routine meteorological observations. The diary entries were imported into a database and the descriptive entries categorised and transformed into ordinal data for statistical analysis, measuring frequencies of weather events or related phenomena. In ranked comparisons, the diary is strongly correlated with established temperature and precipitation datasets, providing confidence in the reliability of the diary as a data source. From the categorised diary data, significant indicators of poor climate are identified, including higher-than-mean occurrences of low pressure, summer cold and rainfall. The years 1817, 1816 and 1823, respectively have the highest number of indicators of poor weather with high or very high significance, totalling 21 over these 3 years, whereas only 11 are recorded in total for the remaining 10 years of data. Thus significant climate anomalies are found in the 2 years following the Tambora 1815 eruption and to a lesser extent 1 year following another major eruption, Galunggung in 1822. As well as colder and wetter summers, other indicators such as optical phenomena, which are not routinely included in climate records, are recorded. There is no evidence that the diarist was aware of the Tambora and Galunggung eruptions at the time of writing. Although the diary covers a relatively short time span and is largely qualitative in nature, it is from an early period, pre-dating the establishment of the UK Meteorological Office, and is unusually methodical. The diary contains a wealth of data which could be further exploited. The current study demonstrates the potential of database technology for categorising and quantifying descriptive data sources in historical climate studies. Copyright (C) 2009 Royal Meteorological Society