An index of summers in Northern Ireland

Abstract

A summer index is presented for Northern Ireland, 1881–1983 to complement those previously published for England and Wales, Scotland, and Ireland as a whole. These sets of indices are compared in discussing the regional variation of summer character within the British Isles. Attempts to identify periodicities of summers of particular character are critically assessed. Markov Chain analysis is applied to the quint sequence of summers in each of the four series, to determine any interdependence between summers. On a year to year basis, results reveal a number of quint summer sequences occurring to be greater, or less, than the random expectations, but overall, no significant single-step first-order Markov memory potential exists. Nor by extending the time interval between events do the four sets of indices reveal statistically significant first-order Markov potential. Markovian analysis shows the complexity of the sequential occurrence of summer character and emphasises the dubious viability of using summer indices for predictive purposes, as has often occurred.