Oceanographic analysis of NAPOLI'85, an experiment in the Tyrrhenian Sea

Abstract

In 1985, an acoustic/oceanographic experiment (NAPOLI '85) was carried out in the Tyrrhenian Sea to investigate acoustic propagation

variability due to inhomogeneities in the ocean medium. In order to provide input parameters for the acoustic theory, the oceanographic medium must be characterised and it is this work which is presented. Data are analysed from thermistor chains, XBT's, CTD's and (most importantly) a towed oscillating

body (TOB) with CTD sensors. The TOB allows ocean properties to be mapped in the vertical-horizont,al plane. These maps show significant oceanic

sub-meso scale features (typically 4 km long x40 m deep) which are tracked

through 10 TOB casts over a three-day period. A procedure for separating internal-wave activity from finestructure is developed and applied. This procedure provides a means to classify the source mechanism for the variability, and hence determine the appropriate treatment. The ocean variability is found to have been almost entirely caused by advective intrusions, with very little internal-wave activity. An internal-wave model is applied to the separated wave field and is shown to agree moderately well. The model cannot be made to match the finestructure field, which has a p - 5 / 2 horizontal wavenumber spectrum. Characteristic length-scale definitions are developed and evaluated for the horizontal and vertical directions. The horizontal length scale is - 2 km and is depth-invariant. Vertical scales vary from 7 to 50 m over the depth range 50-400 m, respectively. The soundspeed

variance has a complicated depth-dependence which can be related to

the observed oceanographic intrusions.