Storminess and cold air outbreaks in NE America during AD 1790-1820

Two hypotheses have been put forward to explain the anomalously deep trough in winter sea-level pressure in the northwestern Atlantic sector during the AD 1790–1820 period. One relates it to an increase in cyclolysis in this area, the other to a change in the general planetary circulation. In an attempt to distinguish between these hypotheses, storminess and cold air outbreaks (CAO) in the northeastern USA during 1790–1820 are studied, based on a record of daily pressure and temperature observations at Salem (Massachusetts, USA). Frequency changes of CAO act as proxy for planetary circulation changes. It is found that CAO in the early period were both more persistent and severe than those in the modern control period. No evidence of elevated levels of storminess in the 1790–1820 period was found. This suggests that the anomalously deep trough can be attributed mainly to a change in the planetary circulation.