An assessment of long-term variability in the NAO, Azores High, and Iceland Low using North Atlantic winds from historical whaling ship logbooks and reanalyses

Abstract

The variability of climate and weather conditions in the North Atlantic and adjacent regions is dominated by multiple modes of climate variability, such as the Atlantic Multidecadal Variability and the North Atlantic Oscillation (NAO). The NAO is one of the region’s most recurrent patterns on interannual to decadal time scales and is often calculated as the pressure difference between the Iceland Low and the Azores High. However, few studies have focused on its centres of action independently, and uncertainties remain about the variations in the associated wind patterns prior to the 20th century. Here, we demonstrate that wind patterns obtained from US whaling ship logbooks from the 19th century from various New England archives align with the predominant wind patterns over the Atlantic region, thus providing invaluable insights into past North Atlantic climate. The logbook data reveals changes in wind speeds that correspond with shifts in the NAO phase and are also seen in reanalysis products. To better understand the NAO’s implications for the winds over the North Atlantic and the individual influences of the Azores High and Iceland Low, we created separate indices for their respective size and positions, allowing us to evaluate their individual behaviour and interactions. Those influences are again compared to the wind patterns provided by the whaling ship logbook data covering the period 1790-1910 CE. There is overall good agreement between the historical data and the reanalysis product, and all differences stay within the variability seen in the individual ensemble members of the reanalysis. Hence, the whaling ship logbook data could be a valuable source to further improve climate indices and thus lead to a better understanding of the long-term context of North Atlantic climate variability.