Some characteristics of the mean annual circulation over the British Isles

The westerly component of the mean annual drift of air over the northern part of the British Isles has, during the last 30 years, attained maxima at intervals mostly of four years. Using this element as an index for classifying the years, the writer sets out the special features which in 1,arious corresponding years have affected weather, temperature, rainfall, sunshine and gales in the British Isles. It is shown that years in which the westerly component of air drift reached a maximum have been characterised on the average by warmer and drier conditions and their summers individually by sunnier conditions than other years of the series; years preceding a maximum (so far as the available statistics enable the point to be explored) appear mostly to have been characterised by a high duration of winds of gale force and by a maximum “latitude‐exchange” of air. Attention is called to the fact that Lockyer, over 30 years ago. noted the existence of a 3–8 year period in atmosphere pressure in India, Australasia and South America, and that more recently Elton, from biological researches and Kershaw from consideration of sunshine data, have remarked on the probability of a climatic factor with a period of about four years.