Seasonal Meridional Shift of the Jet Structure of the Antarctic Circumpolar Current South of Africa.

The paper describes a method for analyzing the seasonal variability of the structure of the gradient field of the absolute dynamic topography (ADT) based on satellite altimetry data. This structure is understood as alternation in the meridional direction of zones of increased values of the ADT gradient modulus and zones of their lower values, i.e. jets and inter-jet gaps. The technique uses linear and harmonic regression analyses and makes it possible to calculate the amplitudes and phases of stationary harmonic oscillations that approximate 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. This technique was used to perform corresponding calculations for the Antarctic Circumpolar Current (ACC) band south of Africa (from 10° W to 25° E). In particular, the amplitude of the seasonal variations of the meridional shift of the ADT gradient field for the ACC as a whole was 0.009 ± 0.013° of 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° of latitude. The amplitude of the variations of the shift of the indicated field with respect to the scale of the ADT itself within the ACC band at different scale values is 0.6–2.5 cm. It is shown that this variations are mainly due to the seasonal variability of the ADT at geographic points. The amplitude of the seasonal variations of the ADT gradient modulus both in latitude and in relation the ADT scale 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. [ABSTRACT FROM AUTHOR]