Abstract

Abstract. Multivariate vertical Empirical Orthogonal Functions (EOF) are calculated for the entire Mediterranean Sea both from observations and model simulations, in order to find the optimal number of vertical modes to represent the upper thermocline vertical structure. For the first time, we show that the large-scale Mediterranean thermohaline vertical structure can be represented by a limited number of vertical multivariate EOFs, and that the "optimal set" can be selected on the basis of general principles. In particular, the EOFs are calculated for the combined temperature and salinity statistics, dividing the Mediterranean Sea into 9 regions and grouping the data seasonally. The criterion used to establish whether a reduced set of EOFs is optimal is based on the analysis of the root mean square residual error between the original data and the profiles reconstructed by the reduced set of EOFs. It was found that the number of EOFs needed to capture the variability contained in the original data changes with geographical region and seasons. In particular, winter data require a smaller number of modes (4–8, depending on the region) than the other seasons (8–9 in summer). Moreover, western Mediterranean regions require more modes than the eastern Mediterranean ones, but this result may depend on the data scarcity in the latter regions. The EOFs computed from the in situ data set are compared to those calculated using data obtained from a model simulation. The main results of this exercise are that the two groups of modes are not strictly comparable but their ability to reproduce observations is the same. Thus, they may be thought of as equivalent sets of basis functions, upon which to project the thermohaline variability of the basin. Key words. Oceanography: general (water masses) – Oceanography: physical (hydrography; instruments and techniques)

Highlights

  • The Mediterranean Sea has been the site of major international scientific programs that have set the scene for the modern study of the thermohaline variability of this basin

  • This paper contributes to the description of the Mediterranean Sea thermohaline structure for general purposes and as part of the necessary knowledge required for the proper assimilation of in situ data with the Optimal Interpolation scheme used in MFSPP (Demirov et al, 2003)

  • Recent works (De Mey and Robinson, 1987; Fukumori and Wunsch, 1991) have shown that multivariate Empirical Orthogonal Functions (EOF) can efficiently synthesize the information contained in the T-S diagrams with the possibility of reducing the size of the representation, since only few modes are able to capture the vertical variability in the ocean

Read more

Summary

Introduction

The Mediterranean Sea has been the site of major international scientific programs that have set the scene for the modern study of the thermohaline variability of this basin. The Mediterranean Forecasting System Pilot Project (MFSPP, Pinardi et al, 2003) has begun investigations for the forecasting of the Mediterranean Sea large-scale circulation based upon the scientific knowledge of the processes, a near real-time observing system (Pinardi et al, 2002) and data assimilation scheme. This paper contributes to the description of the Mediterranean Sea thermohaline structure for general purposes and as part of the necessary knowledge required for the proper assimilation of in situ data with the Optimal Interpolation scheme used in MFSPP (Demirov et al, 2003). The thermohaline vertical structure of world ocean basins is represented by evaluating pertinent temperature-salinity (T-S) diagrams obtainable from in situ data sets. Recent works (De Mey and Robinson, 1987; Fukumori and Wunsch, 1991) have shown that multivariate Empirical Orthogonal Functions (EOF) can efficiently synthesize the information contained in the T-S diagrams with the possibility of reducing the size of the representation, since only few modes are able to capture the vertical variability in the ocean

Methods
Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call