Causes of seasonal change in the south Pacific subtropical high

Recent studies have linked the subtropical highs' seasonal change to changes in the distribution and intensity of tropical precipitation. Mechanisms to explain the change can be grouped into three physical mechanisms: 1) classical downstream "Hadley/Walker" circulation, 2) upstream "Hoskins/Gill" mechanism, and 3) extratropical cyclonic activity. These three mechanisms are reviewed. Evidence pro and con for each mechanism is presented with specific application to the seasonality of the subtropical high off the coasts of Chile and Peru.