Abstract
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.
Highlights
The meridional dipole of sea surface temperature anomalies (SSTA) in the Intra-Americas Seas is a natural climate variability pattern most prominent during spring, which has significant interannual fluctuations strongly related to remote influences (e.g., Muñoz et al 2010; Liu et al 2015)
The Dipole Mode (DM) negative phase responds more to a positive North Atlantic Oscillation (NAO) in the previous winter, revealing a stronger North Atlantic Subtropical High (NASH) acting as an atmospheric block, which justifies the decrease in standard deviation (STD) and a more stable circulation
Higher values of the STD fields indicate that the wind speed or direction is more variable and, the mean value of the wind is less representative, and its variations are the ones that exert a greater influence on the wind-SST coupling
Summary
The meridional dipole of sea surface temperature anomalies (SSTA) in the Intra-Americas Seas is a natural climate variability pattern most prominent during spring, which has significant interannual fluctuations strongly related to remote influences (e.g., Muñoz et al 2010; Liu et al 2015). The dipole consists of SSTA with an opposite sign between the Caribbean Sea and the Gulf of Mexico (CS&GM) This pattern has been observed in the spring following an intense El Niño event (Alexander and Scott 2002). Maldonado et al (2017) and Martinez et al (2020) identified a similar configuration of late winter SSTA as a predictor of precipitation in Central America and the Caribbean during the first peak of the rainy season (May-June), especially of extreme precipitation. This SSTA pattern was associated with tropical North Atlantic (TNA) warming during February. This SSTA pattern was associated with tropical North Atlantic (TNA) warming during February. Alexander and Scott (2002), Muñoz et al (2010), and Liu et al (2015) concur that the SSTA dipole responds mostly to changes in air-sea fluxes, with latent heat flux being the main contributor to this pattern
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