A Continuum Approach to Understanding Changes in the ENSO–Indian Monsoon Relationship

• Published in: Journal of climate Vol. 34; no. 4; pp. 1549 - 1561
• Main Authors: Schulte, Justin, Policelli, Frederick, Zaitchik, Benjamin
• Format: Journal Article
• Language: English
• Published: Goddard Space Flight Center American Meteorological Society 01.02.2021
• Subjects: Anomalies; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; El Nino-Southern Oscillation event-rainfall relationships; Meteorology And Climatology; Monsoons; Rain; Rainfall; Rainfall variability; Sea surface; Sea surface temperature; Sea surface temperature anomalies; Southern Oscillation; Summer monsoon; Surface temperature; Temperature anomalies; Wind; India
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/JCLI-D-20-0027.1

It is well documented that the relationship between the El Niño–Southern Oscillation (ENSO) and the Indian summer monsoon changes on interdecadal time scales, yet an explanation for the variations is still a subject of debate. Here, using a continuum framework based on one-point partial correlation maps, we show that the ENSO–Indian rainfall relationship is influenced by the gradient of sea surface temperature anomalies (SSTA) across the Niño-3 region. Based on this identified SSTA pattern, a simple trans-Niño-3 (TN3) index is created that explains up to 50% of all-India rainfall variability during the mid- to late monsoon season after the 1960s. It is also shown that the influence of the TN3 pattern on the relationship between common ENSO metrics and all-India rainfall is strongest during the August–September (AS) monsoon subseason and weakest during the June–July subseason. The TN3 pattern accounts for up to 80% of the change and sign reversal in the AS Niño-1+2–all-India rainfall relationship in recent decades. The 1940s coincides with the intensification of the TN3 pattern and its influence. As the TN3 index is nearly orthogonal to the Niño-3 index, and both are strongly correlated with all-India rainfall, the strengthening TN3 influence must be systematically associated with the weakening Niño-3–all-India relationship in recent decades. This work supports arguments that recent changes in the ENSO–Indian rainfall relationship are not solely related to noise.