Abstract
The aim of this study is the verification of a new velocity-based feature model, called streamlets, proposed recently for objective analysis of the three-dimensional velocity structure of jet streams and eddies in the oceans. Streamlets are continuously imbedded shearing vortex solenoids having two forms: cylindrical (for jets) or toroidal (for eddies, considered as self-closed jets). Both these forms comprise stream coordinates based on streamlines of maximum velocity as an axis and vertical velocity cross-sections defined as an oblique cone with elliptical base. Assimilation of velocity measurements is accomplished by fitting this cone to available data using the well-known Nelder-Mead simplex downhill algorithm for finding the minimum of nonlinear parametric functions. Advantages of the streamlet model are discussed emphasizing its functional integrity. The focus is on velocity data assimilation based on coherency of synoptic scale features as opposed to usual pointwise assimilation methods such as averaging or optimal interpolation. Case studies present synoptic features of a different origin and scale including surface-intensified and subsurface baroclinic examples as well as deep barotropic ones demonstrating universality of the model. The theory of streamlets is also addressed in this paper, since it further sustain the streamlet model.
Highlights
Feature modeling of jet streams and eddies, termed later as synoptic features for short, is a new and very promising kind of an objective analysis of oceanographic fields
The reason is that by determining ocean dynamics these fields rule all other fields. Due to their high spatial and temporal variability, it is hard to reproduce them by means of formal and instable correlations used in traditional objective analysis
The basic problem with feature modeling is the lack of universality; the velocity-based feature models are not in exclusion since all previously proposed models (e.g., [2, 5]) include empirically selected functions, which must be heuristically assigned for any particular synoptic feature
Summary
Feature modeling of jet streams and eddies, termed later as synoptic features for short, is a new and very promising kind of an objective analysis of oceanographic fields. The advantage of feature models (in comparison to point methods of objective analysis of oceanographic fields) is their integral character, which enables us to solve this very important problem efficiently Another problem, which has appeared in relation to development of numerical models of oceanic currents, is the challenging problem of data assimilation, known as the initialization problem of numerical forecasting. The basic problem with feature modeling is the lack of universality; the velocity-based feature models are not in exclusion since all previously proposed models (e.g., [2, 5]) include empirically selected functions, which must be heuristically assigned for any particular synoptic feature Unlike these empirical models, the streamlet model offered in the communication [6] is universal. The theory of streamlets is addressed here, since the perspective of this paper is to provide observational evidence based on available measurements of several synoptic features to sustain this theory
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