| Popis: |
The Dipole Mode (DM) is the leading pattern of springtime wind-SST coupled interannual variability in the Intra-Americas Seas, characterized by SST anomalies of opposite sign between the Caribbean Sea and the Gulf of Mexico. Using the standard deviation (STD) of the wind in a Maximum Correlation Analysis (MCA), this study aims to provide a more dynamic view of the role of the atmosphere in its coupling with the SST. The MCA reveals that the positive phase of the DM is associated with an increase in atmospheric instability, while the negative phase emerges under more stable atmospheric conditions. The DM is preceded by changes in the subtropical high-pressure belt during the previous winter, particularly in the North Atlantic Subtropical High (NASH), and reflects shifts in the latitudinal position of the subtropical jet stream. The DM positive phase tends to occur after an El Niño winter, under negative North Atlantic Oscillation (NAO) conditions. El Niño modulates the DM through a weakening in the meridional pressure gradient and a southward shift of the jet stream. A negative NAO implies a weaker NASH and, therefore, a more irregular circulation over the region. Both El Niño and negative NAO conditions favor the increase in wind STD during the DM positive phase, consistent with an increment in atmospheric disturbances. The DM negative phase responds more to a positive NAO in the previous winter, revealing a stronger NASH acting as an atmospheric block, which justifies the decrease in STD and a more stable circulation. |
