INTERNAL WAVES IN THE STRAIT OF MESSINA STUDIED BY A NUMERICAL-MODEL AND SYNTHETIC-APERTURE RADAR IMAGES FROM THE ERS-1 2 SATELLITES/

A new numerical two-layer model is presented, which describes the gene ration of internal tidal bores and their disintegration into internal solitary waves in the Strait of Messina. This model is used to explain observations made by the synthetic aperture radar (SAR) from the Euro pean Remote Sensing satellites ERS I and ERS 2. The analysis of availa ble ERS 1/2 SAR data of the Strait of Messina and adjacent sea areas s how that 1) northward as well as southward propagating internal waves are generated in the Strait of Messina, 2) southward propagating inter nal waves are observed more frequently than northward propagating inte rnal waves, 3) sea surface manifestations of southward as well as nort hward propagating internal waves are stronger during periods where a s trong seasonal thermocline is known to be present, 4) southward propag ating internal bores are released from the sill between 1 and 5 hours after maximum northward tidal flow and northward propagating internal bores are released between 2 and 6 hours after maximum southward tidal flow, and 5) the spatial separation between the first two internal so litary waves of southward propagating wave trains is smaller in the pe riod from July to September than in the period from October to June. T he numerical two-layer model is a composite of two models consisting o f 1) a hydrostatic ''generation model,'' which describes the dynamics of the water masses in the region close to the strait's sill, where in ternal bores are generated, and 2) a weakly nonhydrostatic ''propagati on model,'' which describes the dynamics of the water masses outside o f the sill region where internal bores may disintegrate into internal solitary waves. Due to a technique for movable lateral boundaries, the generation model is capable of simulating the dynamics of a lower lay er that may intersect the bottom topography. The proposed generation-p ropagation model depends on one space variable only, but it retains se veral features of a fully three-dimensional model by including a reali stic channel depth and a realistic channel width. It is driven by semi diurnal tidal oscillations of the sea level at the two open boundaries of the model domain. Numerical simulations elucidate several observed characteristics of the internal wave field in the Strait of Messina, such as north-south asymmetry, times of release of the internal bores from the strait's sill, propagation speeds, and spatial separations be tween the first two solitary waves of internal wave trains.