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Abstract
Abstract The standard gravest empirical mode (GEM) technique for utilizing hydrography in concert with integral ocean measurements performs poorly in the southwestern Japan/East Sea (JES) because of a spatially variable seasonal signal and a shallow thermocline. This paper presents a new method that combines the U.S. Navy's Modular Ocean Data Assimilation System (MODAS) static climatology (which implicitly contains the mean seasonal signal) with historical hydrography to construct a “residual GEM” from which profiles of such parameters as temperature (T) and specific volume anomaly (δ) can be estimated from measurements of an integral quantity such as geopotential height or acoustic echo time (τ). This is called the residual GEM technique. In a further refinement, sea surface temperature (SST) measurements are included in the profile determinations. In the southwestern JES, profiles determined by the standard GEM technique capture 70% of the T variance and 64% of the δ variance, while the residual GEM technique using SST captures 89% of the T variance and 84% of the δ variance. The residual GEM technique was applied to optimally interpolated τ measurements from a two-dimensional array of pressure-gauge-equipped inverted echo sounders moored from June 1999 to July 2001 in the southwestern JES, resulting in daily 3D estimated fields of T and δ throughout the region. These estimates are compared with those from direct measurements and good agreement is found between them.
Highlights
The gravest empirical mode (GEM) technique is a method for determining oceanic vertical profiles from vertically integrated quantities
A single inverted echo sounder (IES) measurement, satellite altimeter sea surface height measurement, or expendable bathythermograph (XBT) determination of heat content can provide an estimate of full vertical profiles of T, S, and ␦ when combined with the appropriate GEM fields
The region of MVS, defined as the region where the local minimum rms error at 180 db is at least 0.5ЊC less than the surrounding two maximum rms error regions, occurs for values of Ј Ͻ Ϫ2.5 ms, and these account for less than 12% of the profiles used in the construction of the residual GEMs and less than 4% of the measurements collected by the PIES array
Summary
The gravest empirical mode (GEM) technique is a method for determining oceanic vertical profiles from vertically integrated quantities. Historical hydrography is used to calculate characteristic relationships for temperature (T), salinity (S), and specific volume anomaly (␦) as functions of pressure (p) and a vertically integrated quantity, such as acoustic echo time (, used here), geopotential height (), or heat content. These relationships (when they exist) form lookup tables known as the GEM fields, denoted as TG(p, ), SG(p, ), and ␦G(p, ) (Meinen et al 2002), respectively. What we mean by ‘‘nearly one-toone’’ is that there must be a general grouping of similar profiles about a particular ; that is, each of the profiles having values within a small range of a particular must be similar within an acceptable amount of scatter
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