Weakened influence of El Niño–Southern Oscillation on the zonal shift of the South Asian High after the early 1980s.

Previous studies indicated that El Niño–Southern Oscillation (ENSO) significantly impacts the zonal shift of the South Asian High (SAH) in boreal summer. This analysis reveals that the influence of ENSO on the zonal shift of the SAH has experienced a significant interdecadal weakening around the early 1980s. Specifically, ENSO has a significant relation with the SAH's zonal shift before the early 1980s. However, after the early 1980s, the impact of the ENSO on the SAH is weak. We further examined the physical processes for the interdecadal change of the ENSO–SAH relation. It is indicated that interdecadal change of relationship between ENSO and SAH zonal shift is attributable to change in the connection between ENSO and Indian summer monsoon (ISM). Before the early 1980s, ENSO could exert significant impacts on the ISM and lead to significant condensational latent heating anomalies around the northern Indian Peninsula. The atmospheric heating anomalies around the northern Indian Peninsula trigger an atmospheric wave train extending eastward from North Africa toward the Iranian Plateau (IP), which further leads to changes in the zonal location of the SAH. Hence, the ENSO exerts significant impacts on the summer SAH zonal shift. By contrast, after the early 1980s, ENSO had a weak impact on the ISM and could not lead to apparent atmospheric heating anomalies over IP. As such, ENSO has a weak effect on the SAH zonal shift. Further analysis indicates that interannual variation of the SAH zonal shift is related to an atmospheric wave train over mid–high latitudes of Eurasia after the early 1980s. [ABSTRACT FROM AUTHOR]