Ocean Front Detection with Glider and Satellite-Derived SST Data in the Southern California Current System

Frank C Olaya,Joaquim P Bento,Enric Pallàs-Sanz,Reginaldo Durazo,Vera Oerder

doi:10.3390/rs13245032

Abstract

This study proposes a method to detect ocean fronts from in situ temperature and density glider measurements. This method is applied to data collected along the CalCOFI Line 90, south of the California Current System (CCS), over the 2006–2013 period. It is based on image-processing techniques commonly applied to sea surface temperature (SST) satellite data. Front detection results using glider data are consistent with those obtained in other studies carried out in the CCS. SST images of the Multi-scale Ultra-high Resolution (MUR) dataset were also used to compare the probability of occurrence or front frequency (FF) obtained with the two datasets. Glider and MUR temperatures are highly correlated. Along Line 90, frontal frequency exhibited the same maxima near the transition zone (~130 km offshore) as derived from MUR and glider datasets. However, marked differences were found in the bimonthly FF probability with high (low) front frequency in spring-summer for glider (MUR) data. Methodological differences explaining these contrasting results are investigated. Thermohaline-compensated fronts are more abundant towards the oceanic zone, although most fronts are detected using both temperature and density criteria, indicating a significant contribution of temperature to density in this region.

Highlights

Ocean fronts are elongated structures characterized by abrupt spatial changes in physical, chemical, and biological properties that mark the boundary between different water masses [1]
These dynamic structures are susceptible to frontogenesis by larger-scale deformation flows [2] and baroclinic instabilities occurring over a wide range of spatial and temporal scales [3,4]
To facilitate the identification of frontal zones, this paper introduces an automated method to detect ocean fronts using repeated measurements spanning over seven years and recorded by autonomous underwater vehicles along a California Cooperative Oceanic Fisheries Investigations (CalCOFI) transect located south of the California Current System (CCS)

Summary

Introduction

Ocean fronts are elongated structures characterized by abrupt spatial changes in physical, chemical, and biological properties that mark the boundary between different water masses [1]. Classic methods include algorithms (Sobel, Roberts, or Laplacian) for detecting horizontal gradient intensity that use the first- or second-order derivative as a criterion to determine discontinuities [8,9,10]. Another technique for detecting the boundary between two water masses is based on the analyses of the frequency distribution (histogram) of an SST image [11].

Methods

Results

Discussion

Conclusion