A Feasibility Study of Three-Dimensional Empirical Orthogonal Functions From the NASA JPL Ocean General Circulation Model: Computing, Visualization and Interpretation

Abstract

Existing oceanic studies on either data reconstruction or dynamics often used 2-dimensional empirical orthogonal functions (EOF) for sea surface temperature (SST) and for deep layers. However, large-scale oceanic dynamics, such as equatorial ocean upwelling and arctic ocean ventilation, imply the existence of strong covariance among the temperatures and other parameters between different layers. These ocean dynamics are not best represented in the isolated 2-dimensional layer-by-layer calculations, while the 3-dimensional EOFs have a clear advantage. The purpose of this paper is to demonstrate 3D EOF calculations based on the NASA Jet Propulsion Laboratory (JPL) ocean general circulation model (OGCM) from surface to 5,500 meters depth, with 33 depth layers, 1-degree latitude and longitude spatial resolution, and monthly temporal resolution. We also present visualizations of the 3D EOFs and make physical interpretations of the first two EOFs. Our 3D EOF results demonstrate that (i) the 3D spatial pattern of equatorial ocean upwelling is mainly reflected in the first EOF mode and has its most variabilities within the depth layer between 100 and 400 meters, (ii) the 3D El Niño Southern Oscillation (ENSO) dynamic pattern is mainly reflected in the second EOF mode and is mostly confined from surface to the depth of 150 meters, and (iii) the lead eigenvalue from the 3D EOF calculation appears to contain some signal of oceanic warming. Additionally, our method of weighted 3D EOF computation and our 3D visualization Python code may be useful tools for both climate professionals and students.