Spatial structure of the temperature and salinity fields in the presence of internal waves on the continental shelf of the states of Jalisco and Colima (Mexico)

Ae Filonov

doi:10.7773/cm.v26i1.574

Abstract

A method to filter fluctuations in the hydrophysical properties of the continental shelf, caused by intense internal tides, is proposed. The method is based on a smoothing of the field of the properties analyzed with a filter, the parameters of which are determined by the shape of the spatial correlation function of the field pulsations. The filtering method was tested on data from a fast oceanographic survey, conducted in an area of the monitoring polygon of the waters around Barra de Navidad. The survey was conducted on 25 and 26 November 1995, with an undulating CTD. In one day, 86 vertical profiles of temperature and salinity were obtained from nine transects perpendicular to the coast (survey area of 100 · 25 km) to a depth of 100 m. The filtering algorithm of the internal waves is studied in detail. The field measurements present an analytical shape obtained from an equation in which the elements describe the components: low frequency, pulsating and related to daily behavior. The results of the analysis of the initial temperature and salinity fields with respect to homogeneity and isotropy are discussed, as well as the structural peculiarities of the estimates of the spatial correlation functions. It is observed that the temperature and salinity fields along the shelf, within the limits of the polygon scale, are neither homogenous nor isotropic. The correlation functions of the field pulsations analyzed are more clearly observed in the thermocline. The characteristic scales perpendicular to the coast are smaller than along it. Examples of smoothing the temperature and salinity fields in the thermocline are given.

Highlights

Es conocido que las mareas internas en la plataforma continental originan variaciones verticales significativas de todas las características hidrofísicas
Seiwell (1939) and later Defant (1950) were the first to show that internal tides may cause the temperature and salinity measurements on the continental shelf to provide different results with respect to the geostrophic currents, depending on the tidal phase in which they were taken
Since the publication of Defant’s (1950) work on the reality and illusion in oceanographic measurements in regions with intense internal tide waves, oceanographers became aware of the insurmountable difficulty and ceased to make calculations of the currents even in the Filonov: Estructura espacial de los campos de temperatura y salinidad en presencia de ondas internas corrientes incluso en las partes abiertas y profundas de la plataforma continental, donde el balance geostrófico se puede mantener

Summary

Departamento de Física Universidad de Guadalajara

Se propone un método de filtrado de las fluctuaciones de las características hidrofísicas en la plataforma continental que son causadas por intensas mareas internas. El método se fundamenta en el suavizado del campo de la característica analizada, a través de un filtro cuyos parámetros se determinan por la forma de la función de correlación espacial de las pulsaciones del campo. El método de filtrado se probó con los datos de un levantamiento oceanográfico rápido realizado en una zona del polígono de monitoreo de las aguas en la región de Barra de Navidad. Se muestra que el campo de temperatura y salinidad en la plataforma, en los límites de la escala del polígono, no son homogéneos ni isotrópicos.

INTRODUCTION

Presentación de los campos de temperatura y salinidad en forma analítica

Presentation of temperature and salinity fields in analytical form

Temperatura Salinidad

Filtering algorithm of the internal waves within the polygon

RESULTS