Freshwater Lens Fronts Propagating as Buoyant Gravity Currents in the Equatorial Indian Ocean

Abstract

AbstractFreshwater lenses (FWLs) deposited by rain exhibit local anomalies in surface salinity and temperature. The resulting patchiness in near‐surface density and sea surface temperature influence upper ocean dynamics and air‐sea fluxes of heat. Understanding lens formation and evolution has been a focus of recent observational and modeling efforts. The work presented here integrates near‐surface ocean and atmosphere time series with remote sensing of sea surface disturbances (X‐band radar) to describe properties and kinematics of FWLs in the equatorial Indian Ocean. Twenty‐eight FWLs were observed with diverse temperature‐salinity properties and structure. Fresh salinity anomalies were as large as −1.35 psu at 3 m depth. Associated temperature anomalies ranged from −0.80 to +0.59°C. Ship‐based radar imagery allowed quantification of propagation speeds of 10 FWL fronts. In the reference frame of the moving fluid, the observed speeds are consistent with the linear long wave speed of . These results offer a novel perspective on the evolution of FWLs as gravity currents whose dynamics need to be properly accounted for to assess lens longevity, including persistence of salinity and temperature anomalies, as well as influences on air‐sea interaction.