Temporal derivative of Total Solar Irradiance and anomalous Indian summer monsoon: An empirical evidence for a Sun–climate connection Rajesh Agnihotri a,b , Koushik Dutta c,n , Willie Soon d a Radio and Atmospheric Science Division, National Physical Laboratory, Council of Scientific and Industrial Research, New Delhi 110012, India b National Institute of Oceanography, Council of Scientific and Industrial Research, Dona Paula, Goa 403004, India c Large Lakes Observatory, University of Minnesota-Duluth, 2205 East 5th Street, Duluth, MN 55812, USA d Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 63, Cambridge, MA 02138, USA article info Article history: Received 8 December 2010 Received in revised form 6 June 2011 Accepted 10 June 2011 Available online 25 June 2011 Keywords: Total Solar Irradiance (TSI) Tropical precipitation Indian monsoon Temporal derivative of TSI abstract Identifying the pattern of natural climate variability is of immense importance to delineate the effects of anthropogenic climate changes. Global and regional climates are suspected to vary, in unison or with delays, with the Total Solar Irradiance (TSI) at decadal to centennial timescales. Here we show that the Indian summer monsoon rainfall correlates well with the temporal derivative of TSI on multi-decadal timescales. This linkage between the temporal derivative of TSI and the Indian summer monsoon is tested and corroborated both for the instrumental period (1871–2006) and for the last 300 years using a speleothem d 18 O record representing rainfall in southwestern India. Our analyses indicate that anomalous dry periods of the Indian monsoon are mostly coincident with negative TSI derivative. This study thus demonstrates the potential of ‘TSI derivative’ as an important indicator of natural monsoon variability on an interdecadal timescale. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction Monsoonal precipitation in the densely populated countries of South Asia is a very important component of the global climate system, and has large socio-economic impacts (Khandekar, 2010 and references therein). In anticipated response to global warm- ing caused by anthropogenic activity, several inconsistencies have been predicted to occur in precipitation patterns in both the All India Summer Monsoon Rainfall (AISMR), and globally (Goswami et al., 2006a; Ashfaq et al., 2009). Monsoon rainfall in south Asia is precariously balanced on several boundary conditions ranging from stratosphere to the depth of Indo-Pacific warm pools (e.g., Claud and Terray, 2007; Khandekar, 2009), so that even slight deviations from the normal climatology may result in a significant change in the distribution and amount of rainfall. Acknowledging the concern that anthropogenic activity may impact on global climate through changes in precipitation distribution, it is manda- tory to understand the magnitude and pattern of natural variability in Indian monsoonal precipitation on interdecadal and longer timescales. Numerous proxy based paleo-records from both the northern and the southern hemispheres reveal that intrinsic solar variability acts as a key player in governing decadal to millennial scale climate variation (Verschuren et al., 2000; Bond et al., 2001; Neff et al., 2001; Agnihotri et al., 2002, Burns et al., 2002; Agnihotri and Dutta, 2003; Fleitmann et al., 2003; Hu et al., 2003; Higginson et al., 2004; Gupta et al., 2005; Mangini et al., 2005; Mayewski et al., 2005; Y.J. Wang et al., 2005; Sinha et al., 2007; Kurian et al., 2009). In addition, three recent studies that deal with changes in annually resolved precipita- tion or its direct manifestation (e.g., lake levels, stream flow of major rivers) reinforce the idea of solar-controlled or solar-modulated hydrologic changes (Bhattacharyya and Narasimha, 2005; Stager et al., 2007; Mauas et al., 2008, 2010). All these studies suggest that the relatively small changes in solar energy output represented by Total Solar Irradiance (TSI) control one or more drivers within the Earth’s climate system (Shaviv, 2008) that result in the observed climate change (please see Section 3 below for discussion on other plausible solar drivers and physical mechanisms). The TSI, formerly known as the solar constant, amounts to  1367 W m 2 and is the wavelength-inte- grated energy of solar radiation received at the top of the Earth’s atmosphere, within which perturbations occur in the amount and distribution of magnetic fluxes associated with sunspot variability and additional solar magnetic features (Fontenla et al., 1999; Trujillo Bueno et al., 2004). The Sun is brighter when sunspot numbers are high because brightening effect due to the faculae network out- weighs the darkening effect of sunspots (Fontenla et al., 1999). In-situ TSI data measured by radiometers installed on satellites are available for the last  40 years, and has been used by several Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jastp Journal of Atmospheric and Solar-Terrestrial Physics 1364-6826/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jastp.2011.06.006 n Corresponding author. E-mail addresses: rajagni9@gmail.com (R. Agnihotri), kdutta@d.umn.edu (K. Dutta), wsoon@cfa.harvard.edu (W. Soon). Journal of Atmospheric and Solar-Terrestrial Physics 73 (2011) 1980–1987