Decadal Indian Ocean Influence on the ENSO-Indian Monsoon Teleconnection Mostly Apparent

"Decadal influence" on the El Nino-Southern Oscillation-Indian summer monsoon teleconnection has been much studied but with plurality and ambiguity about the concept of influence. Here (a) we provide formal definitions of the apparent influence of a specific factor on the teleconnection, as correlation coefficients, which enable us to test them as null-hypotheses. Using the recently released Community Earth System Model v2 Large Ensemble data, we show that a 50% chance for the detection of the apparent Indian Ocean influence under stationary conditions might take 2,000 years of data. However, (b) we find that this influence is mostly apparent, causally not dominant, indeed, as it originates more dominantly from fluctuations of the decadal moving window El Nino-Southern Oscillation variability, which causally influences an Indian Ocean Dipole-like moving window mean state. (c) We also show that unattributed so-called "decadal influence," defined as a deviation from a linear regression model of the teleconnection as a null-hypothesis, cannot be detected in twentieth century observations in South Asia even regionally. However, as a new insight, we find our new simple influence concept as a significant correlation coefficient to be possibly consistent with such a null-hypothesis.