Clim. Past Discuss., 9, 3103-3123, 2013
© Author(s) 2013. This work is distributed
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This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
On the low frequency component of the ENSO-Indian Monsoon relationship; a paired proxy perspective
M. Berkelhammer1,2, A. Sinha3, M. Mudelsee4,5, H. Cheng6,7, K. Yoshimura8, and J. Biswas9
1University of Colorado, Boulder, USA
2Cooperative Institute for Research in Environmental Sciences, Boulder, Colorado, USA
3California State University, Dominguez Hills, USA
4Climate Risk Analysis, Hanover, Germany
5Alfred Wegener Institute, Bremerhaven, Germany
6University of Minnesota, Minneapolis, USA
7Institute for Global Environmental Change, Xian Jiatong, China
8Atmospheric and Oceanic Research Institute, Tokyo, Japan
9National Cave Research and Protection Organization, Raipur, India

Abstract. There are a number of clear examples in the instrumental period where positive El Niño events were coincident with a severely weakened summer monsoon over India (ISM). ENSO's influence on the Indian Monsoon has therefore remained the centerpiece of various predictive schemes of ISM rainfall for over a century. The teleconnection between the monsoon and ENSO has undergone a protracted weakening since the late 1980's suggesting the strength of ENSO's influence on the monsoon may vary considerably on multidecadal timescales. The recent weakening has specifically prompted questions as to whether this shift represents a natural mode of climate variability or a fundamental change in ENSO and/or ISM dynamics due to anthropogenic warming. The brevity of empirical observations and large systematic errors in the representation of these two systems in state-of-the-art general circulation models hamper efforts to reliably assess the low frequency nature of this dynamical coupling under varying climate forcings. Here we place the 20th century ENSO-Monsoon relationship in a millennial context by assessing the phase angle between the two systems across the time spectrum using a continuous tree-ring ENSO reconstruction from North America and a speleothem oxygen isotope (δ18O) based reconstruction of the ISM. The results suggest that in the high-frequency domain (≤ 15 yr), El Niño (La Niña) events persistently lead to a weakened (strengthened) monsoon consistent with the observed relationship between the two systems during the instrumental period. However, in the low frequency domain (≥ 60 yr), periods of strong monsoon are, in general, coincident with periods of enhanced ENSO variance. This relationship is opposite to which would be predicted dynamically and leads us to conclude that ENSO is not pacing the prominent multidecadal variability that has characterized the ISM over the last millennium.

Citation: Berkelhammer, M., Sinha, A., Mudelsee, M., Cheng, H., Yoshimura, K., and Biswas, J.: On the low frequency component of the ENSO-Indian Monsoon relationship; a paired proxy perspective, Clim. Past Discuss., 9, 3103-3123, doi:10.5194/cpd-9-3103-2013, 2013.
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