The anomalous winter of 1783–1784: Was the Laki eruption or an analog of the 2009–2010 winter to blame?

[Derecho!]

Thought this was interesting.....

GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L05706, 4 PP., 2011

doi:10.1029/2011GL046696

The anomalous winter of 1783–1784: Was the Laki eruption or an analog of the 2009–2010 winter to blame?

The anomalous winter of 1783–1784: Was the Laki eruption or an analog of the 2009–2010 winter to blame? Rosanne D'Arrigo

Lamont-Doherty Earth Observatory, Earth Institute at Columbia University, Palisades, New York, USA

Richard Seager

Lamont-Doherty Earth Observatory, Earth Institute at Columbia University, Palisades, New York, USA

Jason E. Smerdon

Lamont-Doherty Earth Observatory, Earth Institute at Columbia University, Palisades, New York, USA

Allegra N. LeGrande

NASA Goddard Institute for Space Studies, New York, New York, USA

Edward R. Cook

Lamont-Doherty Earth Observatory, Earth Institute at Columbia University, Palisades, New York, USA

The multi-stage eruption of the Icelandic volcano Laki beginning in June, 1783 is speculated to have caused unusual dry fog and heat in western Europe and cold in North America during the 1783 summer, and record cold and snow the subsequent winter across the circum-North Atlantic. Despite the many indisputable impacts of the Laki eruption, however, its effect on climate, particularly during the 1783–1784 winter, may be the most poorly constrained. Here we test an alternative explanation for the unusual conditions during this time: that they were caused primarily by a combined negative phase of the North Atlantic Oscillation (NAO) and an El Niño-Southern Oscillation (ENSO) warm event. A similar combination of NAO-ENSO phases was identified as the cause of record cold and snowy conditions during the 2009–2010 winter in Europe and eastern North America. 600-year tree-ring reconstructions of NAO and ENSO indices reveal values in the 1783–1784 winter second only to their combined severity in 2009–2010. Data sources and model simulations support our hypothesis that a combined, negative NAO-ENSO warm phase was the dominant cause of the anomalous winter of 1783–1784, and that these events likely resulted from natural variability unconnected to Laki.

[Roger Smith]

There are some weather records from Fort Dearborn (Detroit) from 1783-84 that show the following general patterns:

** the previous winter looks unremarkable

** spring 1783 looks fairly warm, April had several days with mid-day readings above 80 F.

** summer 1783 saw a rather abrupt change to anomalous cold.

..... by modern standards, July was exceptionally cold. The period 13th to 16th had highs only near 60 F. This would seem to indicate some very unusual circulation patterns over the region to the north of the Great Lakes.

** autumn 1783 returned to a more normal regime, October was reasonably warm, November did not get very cold although mild days were infrequent.

** then came the very cold winter but this did not really start until around the 20th of December, before that, it was actually very mild at times (highs above 60 F around the 10th).

This all sounds like specific analogues might be tough to find. Nowadays we would think four days with highs near 70 F would be very cool, let alone closer to 60F in July. Seems like a pattern where volcanic dust may have spread west into the eastern Canadian arctic and then the Hudson Bay region but was having no effect on the Pacific, so the climate kept oscillating between mild westerly and anomalously cold northerly circulation types.

By the way, the lowest temperature in the records during the winter of 1783-84 was -18 F on the morning of the 27th of January and the January mean temperature appears to have been only 6 to 8 F. These temperatures are from three daily readings and not daily extremes.