Abstract/Summary

Previous studies have established the existence of a large-scale teleconnection between ascent in the South Asian Summer Monsoon and subsidence over the Mediterranean (known as “the monsoon–desert mechanism”). Improving the representation of this mechanism could potentially improve the skill of seasonal forecasts for European summer weather patterns. In this study, the impact of air–sea coupling on the NH summer climate and the representation of the monsoon–desert mechanism is analysed in two 45-year experiments with the Met-Office Unified Model. In the first coupled experiment, the atmosphere is allowed to freely interact with a high-vertical-resolution mixed-layer ocean model. The diagnosed daily SSTs from this experiment are then used to force an atmosphere-only uncoupled experiment. The two experiments have a similar mean state, but the coupled experiment has a substantially more realistic representation of interannual precipitation variability over the Indian Summer Monsoon region. The coupled experiment can capture the observed westward propagating Rossby-wave trains excited by the Indian Summer Monsoon, while in the uncoupled experiment the Rossby-wave response is more local. It is shown that in the coupled experiment more moisture is transported inland and monsoon precipitation reaches further north, which favours westward Rossby wave propagation. Finally, evidence is shown that the coupled experiment can capture the observed interannual relationship between the Indian Summer Monsoon precipitation and precipitation over the Balkans/Black Sea region.