Influence of the subtropical ridge on directional wave power in the southeast Indian Ocean

Abstract

Changes in the intensity and position of subtropical anticyclones are major drivers of wave climate around Australia. The quasi-stationary ridge of high atmospheric pressure in the mid-latitudes is known as the Subtropical Ridge (STR). In this study, we decompose the directional wave climate along the Western Australian Shelf (WAS) into three primary modes of variability using a statistical-synoptic typing approach, and relate the wave power signatures of each to movements in the STR. We find a significant reduction in wave power along the WAS over the past 35 years. This is synonymous with an intensification of the STR resulting in blocking of powerful Southern Ocean Low wave conditions, a small increase in weaker anticyclonic waves, and a reduction in total wave power. A persistent intensification and/or poleward shift in the STR, associated with anthropogenic warming, may result in a continued decrease and anticlockwise rotation in wave power along the WAS. The approach taken in this article relates empirical changes in wave climate to movements in large-scale climate drivers which can be used to complement the understanding of climate-model based scenarios of wave climate change.