Behaviour of the centres of action above the Atlantic since 1881. Part II: Associations with regional climate anomalies

Abstract

This paper constitutes the second part of the analysis of the behaviour of centres of action above the Atlantic since 1881. The present study examines the applicability of the generated time series of the central pressure and geographical location of the Iceland Low (IL), Azores High (AH), Inter Tropical Convergence Zone (ITCZ) and South Atlantic Subtropical High (SSH) to the description of the surface circulation and its influence on the climate anomalies above the Atlantic and adjacent land areas in the period 1950—1989. Using the normalized anomalies of the pressure gradient between the cores of the AH and IL (AH—IL gradient) as a NAG (North Atlantic Oscillation) index, it can be shown that t his index is a practicable tool for the detection of characteristic spatial anomaly patterns in different climate variables above the North Atlantic and surrounding land areas. The ‘strong’ NAG (the AH-IL gradient above ‘normal’) in winter leads to a warming above northern and central Europe as well as to the development of the dipole-like anomaly patterns in the wind speed, sea-surface temperature, surface and tropospheric temperature and other variables above the western and eastern North Atlantic. The composite analysis for the ‘weak’ NAG reveals inverse patterns. The application of the characteristic parameters of the ITCZ and of the two subtropical highs as predictors of the rainfall variability in northeast Brazil and the Sahel for the period 1950-1983 shows that for the most part, these variations can be explained by the anomalies of the latitude position and intensity of the ITCZ. © 1998 Royal Meteorological Society. Int. J. Climatol., 18, 23-36 (1998) No. of Figures: 3. No. of Tables: 5. No. of