%0 Journal Article
%T Internal Solitary Waves in the Brazilian SE Continental Shelf: Observations by Synthetic Aperture Radar
%A Jo£¿o A. Lorenzzetti
%A Fabian G. Dias
%J International Journal of Oceanography
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/403259
%X We present an analysis of internal solitary waves (ISWs) on the SE Brazilian continental shelf using a set of Envisat/ASAR satellite images. For the 17-month observation period, 467 ISW packets were detected. Most of observed solitons were associated to 4¨C6£¿ wind. The number of ISW packets shows a seasonal signal with a peak in summer, with higher concentration in the outer shelf in all seasons, followed by midshelf during the summer. Propagation direction of ISWs was predominantly onshore with packets separated by typical internal tide wavelengths (~10¨C40£¿km). The highest values of the barotropic tidal forcing F are concentrated at the shelf break between 200 and 500£¿m isobaths. These characteristics suggest that ISWs are formed from nonlinear disintegration of internal tides generated at the shelf break that propagate shoreward as interfacial internal waves. No significant change in the number of ISWs from spring to neap tides was observed in spite of significant tidal current variation (60%). Even not being a region of strong tides, this study shows that ISWs are a frequent and widespread feature, possibly playing a significant dynamic role, affecting biological production, sediment dispersion, and transport. 1. Introduction Since the launch of SEASAT in 1978, numerous studies of oceanic internal solitary waves (ISWs) have been made using synthetic aperture radar (SAR) images. The availability of a great number of SAR satellite images has shown that ISWs are an ubiquitous oceanic phenomenon. They are frequently observed wherever tidal currents and stratification occur near significant seafloor topographic features, such as shelf break zones, plateaus, or sills [1]. Although a large number of remote sensing studies of ISWs have used SAR images, these features can also be observed in ocean color imagery [2] and in Sun glitter regions of visible images [3]. ISWs normally appear in SAR images as packets of 2¨C8 dark and bright stripes, with subsequent packets separated by distances corresponding to the wavelength of the internal tides (Figure 1) [1, 4]. Figure 1: Example of two ISWs packets generated at consecutive tidal cycles observed on the Brazilian southeast coast. Image acquisition date: February 3, 2010; geographic position is indicated at insert box in Figure 2. At typical microwave frequencies used in SAR systems (1¨C10£¿GHz), the penetration depth of radar pulses in sea water, which is dependent on the complex permittivity, is restricted to less than about one centimeter [5]. Although practically a surface phenomenon, the backscattering of SAR
%U http://www.hindawi.com/journals/ijocean/2013/403259/