Sensitivity of a tropical-temperate trough to sea-surface temperature anomalies in the Agulhas retroflection region

The Colorado State University Regional Atmospheric Modelling System's (RAMS) sensitivity to positive variations in sea-surface temperature is tested by adding positive anomalous temperatures to the ocean surface in the region of the Agulhas Current retroflection for a simulated period of four days from 21 to 24 January 1981. The simulated circulation and precipitation values of the sensitivity test are compared with a control simulation. The results of the experiment, although limited in response did result in noticeable increases in convective precipitation and are consistent with the expected climate responses to anomalously high sea-surface temperatures in this area. These simulated circulation Changes are consistent with previously hypothesised features of ocean-atmosphere interaction for the Agulhas Current region. The development of the ocean anomaly served to intensify the sea-surface temperature front, leading to a poleward shift in the near-surface westerlies. The strengthened heat flux resulting from the higher ocean temperatures enhanced low-level instability initially over the modified sea-surface temperature field and then eastwards along the coast by the passage of the westerly troughs.