Analysis of the quasi-two-year variation of the Zapiola Anticyclone based on the reanalysis data and drifter trajectories

Zapiola anticyclone (ZA) is an anticyclonic circulation trapped by a seamount about 1200 m in height named Zapiola Rise (ZR). The ZA is adjacent to energetic flows of the South Atlantic Ocean, such as the Brazil/Malvinas Confluence (BMC) and the Antarctic Circumpolar Circulation (ACC). The interplay among the circulations makes the dynamic processes of the ZA complex and variable. Based on the reanalysis data and drifter observations, this study mainly aims to investigate the influence of a strong flow field outside of the seamount on variations of the ZA. Results show that the vorticity of the ZA has a significant quasi-two-year variation, which is an independent eigenmode in the basin. The advection of the potential vorticity over the bottom topography from the southern boundary plays the most significant role in controlling the vorticity variations of the ZA. Drifter trajectories also confirm the importance of the flow field in the south of the seamount. The statistical results of the drifter trajectories show that the transport process of the southern boundary flow field has the most significant effect on the dynamic processes of the ZA. It is worth mentioning that the results obtained using the dataset of the reanalysis are limited by its validity in the region.

Automated summary

This study investigates the influence of the interaction between Zapiola anticyclone (ZA) and South Atlantic Ocean flows on the dynamic processes of ZA. The results show that the vorticity of ZA has a significant quasi-two-year variation, which is mainly affected by the advection of potential vorticity over the bottom topography from the southern boundary. The flow field also plays an important role in the dynamic processes of ZA.