Exploring the seasonal characteristics of the equatorial Atlantic SSTA: insights from an extended recharge-discharge oscillator framework

The equatorial Atlantic (EA) sea surface temperature anomalies (SSTA) exhibit significant interannual variability, typically peaking during the boreal summer months from May to August. In this study, we utilize an extended recharge-discharge oscillator (RO) model, considering both coupled Atlantic ocean–atmosphere interactions and the remote influence of Pacific ENSO forcing, to explore the dynamics of EA SSTA seasonality. Our results demonstrate that this extended RO model captures the temporal characteristics of EA SSTA well, especially its seasonal variation. Further analysis suggests that the seasonality of EA SSTA is primarily governed by the seasonal modulation of the EA SSTA growth rate, characterized by a robust seasonal cycle that transitions from positive to negative during boreal summer. In contrast, the EA SSTA phase transition rate and the ENSO forcing coefficient contribute relatively little to the seasonal preference of EA SSTA. In most climate models, EA SSTA also shows a tendency to peak during the boreal summer; however, the seasonal preference is significantly weaker compared to observations. This weaker preference in climate models primarily results from the smaller contribution of the EA SSTA growth rate, which is mainly due to the lower (more negative) annual mean of the growth rate and secondarily due to the weaker seasonal cycle amplitude of the growth rate.