Variability of the North Atlantic subtropical high and associations with tropical sea-surface temperature

Based on generated time series of the central pressure of the subtropical high, the behaviour of this atmospheric centre of action has been examined since 1950 with regard to the inter-annual variations, persistence, linear trends, abrupt change, spectral analysis and interactions. The year-to-year variations in the central pressure of the subtropical high are considerable. The pronounced strengthening of the subtropical high during approximately the last 20 years is its most remarkable feature. Variations in the subtropical high's intensity seem to follow a cyclic pattern. Statistically significant abrupt onset events are found, with the majority occurring in winter. Increasing and decreasing episodes have occurred in the late 1960s and early 1980s. According to spectral analysis, it can be assumed that the centre of action of the subtropical high is characterized by non-periodic behaviour. The peaks occur only at the lowest frequency. The quasi-biennial oscillation may affect the subtropical high in the winter season, whereas the North Atlantic Ocean may affect the subtropical high in summer. There is no detectable connection between El Nino-southern oscillation and the subtropical high in either season. The subtropical high has been affected by sea-surface temperatures of the north and south tropical Atlantic. with negative and positive signs respectively in the winter season. Interactions between the subtropical high and sea-surface temperatures over the tropical Atlantic Ocean are absent in the summer season. Copyright (C) 2004 Royal Meteorological Society.