The Interaction Between the Mesoscale and Gyre-Scale Variabilities of the Argentine Basin
Jet Propulsion Laboratory,
Pasadena, CA 91109,
The ocean is a turbulent fluid characterized by interactions among a wide range of spatial and temporal scales. The Argentine Basin of the South Atlantic Ocean is an ideal region to study the interaction between mesoscale eddies and gyre-scale waves and currents. The confluence of the Malvinas and Brazil Currents creates mesoscale meanders and eddies with energy levels ranked at the top of the world’s oceans. Surrounded by the energetic mesoscale variability is a gyre of anticyclonic barotropic circulation, superimposed by rapidly-rotating, gyre-scale, high-frequency waves (25-day period). Decade-long altimetric observations of sea surface height have provided a unique opportunity to study the relationship between the mesoscale and gyre-scale variabilities of the region. The high accuracy and temporal sampling of TOPEX/Poseidon (T/P) and Jason data have allowed the detection of the high-frequency gyre-scale waves, whereas the enhanced spatial resolution provided by the merging of T/P and Jason data with ERS-1 and -2 data enables the synoptic analysis of the mesoscale variability. Some interesting properties of cross-scale interactions were discovered. The amplitude of the high-frequency gyre-scale waves is highly intermittent with dominant periods in the range of 110-150 days. Within this period band, the wave amplitude is coherent with the energy level of the mesoscale variability: When the mesoscale energy level goes down, the wave amplitude goes up, and vice versa, suggesting an exchange of energy between the two scales. The time-lagged correlation of the mesoscale variability reveals a pattern of anticyclonic movement of eddies and meanders, suggesting an interesting relation between them and the mean circulation of the Argentine Basin. These findings provide motivations for further theoretical and modeling investigations of the nature of the interactions and the role of mesoscale variability in determining the general circulation of the region.