Seasonal Meridional Displacement of the Jet Structure of the Antarctic Circumpolar Current South of Africa

Abstract

This paper describes a method for analyzing the seasonal variability of the structure of the gradient field of Absolute Dynamic Topography (ADT) based on the satellite altimetry data. This structure is understood as the alternation in the meridional direction of the zones of increased values of the absolute values of the ADT gradient and the zones of their lower values, i.e. jets and inter-jet gaps. The technique uses linear and harmonic regression analyzes and makes it possible to calculate the amplitudes and phases of stationary harmonic oscillations that approximate the seasonal variations in the meridional shift of the structure of the ADT gradient field and in the absolute values of the ADT gradient, as well as to estimate the calculation error. Based on this technique, corresponding calculations were made for the Antarctic Circumpolar Current (ACC) band south of Africa (from 10 ° W to 25 ° E). In particular, the amplitude of the seasonal variation of the meridional shift of the ADT gradient field for the ACC as a whole was 0.009 ± 0.013° latitude with a maximum northward shift in December. At the same time, there are zones within the ACC band where this amplitude reaches 0.12°, 0.16° and 0.28° latitude. The amplitude of the shift of the indicated field relative to the scale of the ADT itself within the ACC band at different scales is 0.6–2.5 cm. It is shown that this shift is mainly due to the seasonal variation of the ADT at geographic points. The amplitude of the seasonal variation of the ADT gradient modulus relative to both latitude and the ADT scales increases from 1 × 10–3 cm/km in the central part of the ACC to 6–7 × 10–3 cm/km at the southern and northern peripheries.