A Dynamic Dipole: Longterm Mesoscale Oscillation in the Arabian Gulf

The Arabian Gulf (also referred to as the Persian Gulf) can exhibit energetic mesoscale dynamics despite its semi enclosed geometry. Using the GLORYS12V1 ocean reanalysis (1993–2020), this study assesses longterm patterns in sea surface height (SSH) variability and the dominant forces shaping them. The results reveal two persistent low SSH systems: one located in the northwestern part of the basin and the other in the southern Gulf. These features act as focal points of mesoscale circulation. Both systems intensify during the summer season, when atmospheric forcing and surface buoyancy losses are strongest. Their locations coincide with regions of enhanced mixing and surface cooling, suggesting a possible role in the Gulf deep water formation.

Seasonal circulation analysis indicates a summer cyclonic regime influenced by the Iranian coastal current and the Gulf coastal current, which interact with and modulate the two eddies. SSH and Eddy Kinetic Energy (EKE) fields display interannual alternation in the dominance of each eddy, highlighting their unequal sensitivity to regional dynamical conditions and basin-scale climate variability. Three dominant modes were identified using Empirical Orthogonal Function (EOF) analysis: a basin wide meridional gradient (EOF1), a two eddy dipolar mode linked to wind variability (EOF2), and southern eddy mode (EOF3) associated with the Indian Ocean Dipole Mode Index (DMI). Together, these modes describe a recurring low-frequency exchange of energy between the northern and southern eddies.