Reexamining the Indian Summer Monsoon Rainfall–ENSO Relationship From Its Recovery in the 21 st Century: Role of the Indian Ocean SST Anomaly Associated With Types of ENSO Evolution

• Published in: Geophysical research letters 2021-06, Vol.48 (12)
• Main Authors: Yu, Shi‐Yun, Fan, Lei, Zhang, Yu, Zheng, Xiao‐Tong, Li, Ziguang
• Format: Article
• Language: English
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL092873

This study found that the relationship between the Indian Summer Monsoon Rainfall (ISMR) and El Niño‐Southern Oscillation (ENSO) has recovered since 2001, and the relationship strength is closely related to the summer tropical Indian Ocean (TIO) sea surface temperature (SST) anomaly, with the TIO warming (cooling) indicating a stronger (weaker) relationship. Under the same El Niño/La Niña scenario, different signs of the TIO anomaly indicate distinct atmospheric circulation anomalies over the Indian Ocean, thus affecting the ISMR–ENSO relationship. The TIO anomaly is principally associated with different types of ENSO temporal evolution. Strong El Niño events with an early onset, and the transition of El Niño to La Niña, tend to have a warmer TIO and a stronger ISMR–ENSO relationship, in contrast to most of the cases of a decaying La Niña or a La Niña that persists throughout the year. The result brings a prospect for improving the ISMR prediction. Conventionally, the Indian Summer Monsoon rainfall (ISMR) is affected by warmer‐ or colder‐than‐normal sea surface temperature (SST) anomalies in the central‐eastern Pacific, known as the El Niño or La Niña phenomenon, respectively. Thus, a negative relationship exists between the ISMR and El Niño–Southern Oscillation (ENSO). Records show that the relationship weakened after 1980, which affected the prediction of ISMR. The mechanisms of the weakening are still under debate. This study found that the relationship has recovered since 2001. The intensity of the relationship is closely related to the tropical Indian Ocean (TIO) SST anomaly during the monsoon season, with a warmer TIO indicating a much stronger ISMR–ENSO relationship, or vice versa. The source of the TIO SST anomaly is largely attributed to different types of temporal evolution of ENSO. These results indicate that prediction of ISMR can be improved by deciding whether to use ENSO as a basis according to the forecast of the TIO SST. Over the 21 st century, the Indian Summer Monsoon Rainfall (ISMR)–El Niño‐Southern Oscillation (ENSO) relationship has strengthened and almost recovered to its pre‐1980 level On interannual and decadal timescales, the tropical Indian Ocean warming (cooling) indicates a stronger (weaker) Indian Summer Monsoon Rainfall (ISMR)–El Niño‐Southern Oscillation (ENSO) relationship The Indian Ocean basin‐wide sea surface temperature anomaly in summer is related to different types of temporal evolution of El Niño‐Southern Oscillation