A New Study of the Mediterranean Outflow, Air–Sea Interactions, and Meddies Using Multisensor Data

Abstract

Previous studies of the Mediterranean Sea outflow and meddies (O&M) were limited by the poor spatial and temporal resolution of conventional in situ observations as well as the confinement of satellite observations to the ocean?s surface. Accordingly, little is known about the formation and transport of meddies and the spatial and temporal variation of O&M trajectories, which are located, on average, at a depth of 1000 m. However, a new remote sensing method has been developed by the authors to observe and study the O&M through unique approaches in satellite multisensor data integration analyses. Satellite altimeter, scatterometer, infrared satellite imagery, and XBT data were used to detect and calculate the trajectories and the relative transport of the O&M (January 1993?December 2002). Two experiments [covering 1993?95: A Mediterranean Undercurrent Seeding Experiment (AMUSE) and Structures des Echanges Mer?Atmosphère, Propriétés des Hétérogénéités Océaniques: Recherche Expérimentale (SEMAPHORE)] and XBT temperature measurements were used to directly validate the method presented herein. The monthly mean features derived from floats and XBTs for multiple meddies and the results of the presented method were significantly correlated based on a statistical chi-square test. In addition, the complex singular value decomposition method was used to identify the propagating features and their phase speeds. It was found that saltier water from the Mediterranean Sea was transported into the North Atlantic Ocean over the Strait of Gibraltar in boreal spring and summer relative to boreal autumn and winter. Streamfunctions using altimetry, and time?frequency energy distributions using the Hilbert?Huang transform, were computed to evaluate the meddy interactions with the sea surface variation. Since the O&M play a significant role in carrying salty water from the Mediterranean Sea into the Atlantic, such new knowledge about their trajectories, transport, and life histories is important to the understanding of their mixing and interaction with North Atlantic water. This may lead to a better understanding of the global ocean circulation and global climate change.