Impact of preceding Arctic Oscillation anomaly on the zonal displacement of the South Asian High in July

Using various observations and the linear baroclinic model (LBM), this study investigates the impact of out-of-phase variations in the Arctic Oscillation (AO) between March and April on the zonal shift of the South Asian High (SAH) in July. The results indicate that a negative AO in March followed by a positive AO in April can lead to an eastward shift of the SAH in July, and vice versa. This out-of-phase AO variation accounts for approximately 23 % of the interannual variation in the zonal shift of the SAH in July. Further analysis reveals that a negative AO in March induces positive sea surface temperature (SST) anomalies over the high-latitude North Atlantic by modulating surface heat fluxes and zonal SST advection. In April, the atmospheric circulation associated with the positive AO causes positive SST anomalies to develop to the west of Europe. Due to the ocean memory effect, these positive SST anomalies persist into July, leading to positive geopotential height anomalies in the troposphere and lower stratosphere over Northern Europe in July through eddy-mediated processes. The vorticity anomalies associated with the geopotential height anomalies trigger Rossby wave trains over Eurasia, characterized by negative geopotential height anomalies over the northwestern SAH and positive geopotential height anomalies over the eastern SAH, ultimately resulting in an eastward shift of the SAH.