Limits of the existence of the Kuroshio and Gulf Stream currents owing to climate trends

Abstract

Based on the variational property of the energy scattering minimum, this paper presents a model of a zonal jet current applied to the Kuroshio Extension and Gulf Stream after their separation from the western boundary and their turning to the east. The model suggests the following features: (1) the condition of jet existence is the asymmetric current shape with a sharp northern boundary; (2) the dynamic current axis is located south of the convergence axis (this is one of the mechanisms of the formation of two-(multi)front structures in the ocean represented by the Subarctic Front and Kuroshio Extension); and (3) there is a critical parameter range beyond which the current is not the jet current anymore. The modern climate warming tendency is approaching a critical state, when a change in the circulation structure is expected. 1. The object of our research is the transversal structure of a geostrophic jet current applied to the Kuroshio Extension and Gulf Stream oceanic currents after their separation from the coast between 30°–40° N and their eastward turn. Jet character, permanence, and spatiotemporal stability are the properties of these currents on a climatic scale [1, 2]. The parameters of the current are as follows: width ~100 km, depth 1 km, velocity 1 m/s, and water discharge 50 × 10 6 m 3 /s. The aim of this research is to determine the limits of conservation of the jet current under variation of the external parameters owing to possible climatic trends. 2. Variation formulation. The transversal structure of a zonally uniform geostrophic jet current is modeled on a climatic scale with consideration of the detailed structure (influence of the bottom topography and meandering). The origin of coordinates is at the ocean