A contribution to the study of action centres in the North Atlantic

The North Atlantic High appears notably weakened from the beginning of the examined period (1873–1980) until the beginning of this century. From then until 1930, it exhibits an increased central pressure. From the beginning of the period until 1914, the North Atlantic High exhibits a significant trend of intensification and at the same time a trend of displacement to the west. From 1915 until 1963 it exhibits a trend of weakening and a trend of eastward displacement. The North Atlantic Low has not exhibited a significant trend of its central pressure, but it has shown a small trend of displacement to the west. There is generally a negative correlation between the pressures of these two centres of action and a positive correlation between latitudinal position of the centres. The meridional component of the pressure gradient created between the two action centres, appears to have low values during epochs of low frequency of westerlies and high values when the westerlies are more frequent.