Atmospheric circulation and climate of the Euro-Atlantic sector since 1685 based on new directional flow indices

• Main Author: Mellado Cano, Javier
• Other Authors: Trigo, Ricardo Machado, Barriopedro, David
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2020
• Subjects: Ships’ logbooks; Euro-Atlantic atmospheric circulation; North Atlantic Oscillation; Jet Stream; Past European Climate; Domínio/Área Científica::Ciências Naturais::Ciências da Terra e do Ambiente; North Atlantic; North Atlantic oscillation
• Online Access: http://hdl.handle.net/10451/42533

Knowledge of atmospheric circulation beyond the mid-18th century is hampered by the scarcity of instrumental records, particularly over the Ocean. In this regard, wind direction observations kept in ships’ logbooks are a consolidated but underexploited instrumental source of climatic information. In this Thesis we present four monthly indices of wind persistence, one for each cardinal direction, based on daily wind direction observations taken aboard ships over the English Channel. These Directional Indices (DIs) are the longest observational record of atmospheric circulation to date, covering the 1685-2014 period. DIs anomalies are associated with near-surface climatic signals over large areas of Europe in all seasons, being excellent benchmarks for proxy calibrations. DIs series are dominated by large interannual-to-interdecadal variability and provide all year-round observational evidences of atmospheric circulation responses to external forcings (tropical volcanic eruptions) or the role of the atmospheric circulation in anomalous periods such as the Late Maunder Minimum (LMM, 1675-1715). In both cases, the results emphasize complex patterns that are more heterogeneous than previously thought, with contrasting spatial signals in both circulation and temperature. When considered together, DIs explain a considerable amount of European climate variability, improving that accounted for by single modes of variability. This allows us to yield the longest instrumental-based series of the winter North Atlantic Oscillation (NAO) and East Atlantic (EA). The results highlight the role of EA in shaping the North Atlantic action centers and the NAO’s European climate responses. Transitions in the NAO/EA phase space have been recurrent and explain non-stationary NAO signatures and anomalous periods. NAO and EA have additive effects on the jet speed but opposite impacts on the jet latitude, allowing us to derive the first instrumental reconstruction of the North Atlantic eddy-driven jet stream for the last three centuries.