Atmospheric effects in Scotland of the AD 1783-84 Laki eruption in Iceland

Daily weather diaries and meteorological records from Scotland reveal complex weather patterns following the 1783-84 fissure eruption of the Laki volcano, Iceland. Four diarists in eastern and northern Scotland describe the near-simultaneous occurrence of discrete groups of days characterised by 'foggy', 'gloomy' and 'hazy' conditions during June and July 1783. The weather records suggest that an ash-rich portion of the initial plume may have arrived synchronously across eastern Scotland on June 15th, 5 days after the first eruption in Iceland, and lingered for between 5 and 7 days. Following a 3-day interval of fine weather, a sulphurous haze arrived on June 24th and persisted for the rest of the summer. As the summer progressed air pollution episodes became shorter, less frequent and more influenced by air pressure fluctuations. The effect of the eruption on Scotland's climate is unclear although a negative air temperature anomaly of 1.5 degrees C to 2.5 degrees C below the decadal average occurred in September 1783 lasting for 16 days at Dalkeith and 33 days at Fochabers. The 1783-84 winter in Scotland was one of the coldest in recent centuries and was accompanied by prolonged snow and frost through the first 4 months of 1784. During this period, temperatures in eastern Scotland averaged 2.0 degrees C to 2.6 degrees C below the decadal average. The duration and amplitude of post-eruption negative temperature anomalies appear to have been strongly associated with synoptic air pressure and wind flow patterns and not simply related to volcanically-forced cooling. This challenges the hypothesis that the Laki eruptions were responsible for the sustained lowering of air temperatures over the three successive winters of 1783-84, 1784-85 and 1785-86.