The Influences of the North Atlantic Oscillation, the EL Niño/Southern Oscillation and the Quasi-Biennial Oscillation on Winter Precipitation in Ireland

Abstract

Ireland’s winter precipitation, while on average moderately high and very persistent, is highly variable. Three sources of this variability are examined: the North Atlantic Oscillation (NAO), the El Niño/Southern Oscillation (ENSO), and the Quasi-Biennial Oscillation (QBO). The effects of the NAO, ENSO and QBO, singly and jointly, on winter circulation patterns over the North America, the North Atlantic and Europe are described, with particular emphasis on their effects on the disposition of the westerlies and the tracks of extratropical cyclones, the principal sources of winter precipitation over Ireland. Each winter (December-February) from 1957 to 1987 was categorised as to its phase of each of the NAO, ENSO and QBO, and from twelve synoptic stations Ireland’s precipitation was categorised as above average, average or below average. Contingency tables of precipitation and oscillation phase were produced. These indicate that there was above average precipitation when the NAO was well positive (strong westerlies), below average precipitation when the ENSO was well positive (‘High/Dry’, but a more conventional ENSO classification yielded a much weaker association) and a tendency for above average precipitation during sunspot maxima particularly in the northern half of Ireland in QBO West phase. When ENSO was not well positive and during sunspot minima, precipitation in the north and west was above average when QBO phase was East and below average when QBO phase was West.KeywordsSunspot NumberNorth Atlantic OscillationWinter PrecipitationNorth Atlantic Oscillation IndexNorth Atlantic Oscillation PhaseThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.