Changes in ENSO-monsoon relations from early to recent decades during onset, peak and withdrawal phases of Indian summer
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Changes in ENSO‑monsoon relations from early to recent decades during onset, peak and withdrawal phases of Indian summer monsoon P. H. Hrudya1 · Hamza Varikoden2 · R. Vishnu1 · J. Kuttippurath3 Received: 19 December 2019 / Accepted: 12 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The El Niño Southern Oscillation (ENSO) is an important coupled ocean–atmosphere phenomenon in the tropical Pacific and an important modulator of the spatio-temporal variability of Indian summer monsoon rainfall (ISMR). Here, we explore the impact of ENSO during onset (June), peak (July–August) and withdrawal (September) phases of ISMR for the period 1951–2015, by studying the changes in the ENSO-monsoon relationship from early decades (1951–1980) to recent decades (1986–2015). We observe noticeable changes in the ENSO-monsoon relationship from the early to recent decades during all the three phases. During El Niño events, rainfall over most of the Indian regions is significantly increased in recent decades during onset phase, but a significant decrease in rainfall is observed during peak and withdrawal phases. On the other hand, the rainfall during La Niña events is significantly decreased over the monsoon core zone of India during all the three phases. A significant increase (decrease) in sea surface temperature (SST) is observed over the central equatorial Pacific and Indian Ocean during El Niño (La Niña) events in recent decades. These changes differ from one phase to another and related to the observed rainfall patterns over the Indian region. Apart from these, the changes in the anomalies of low level circulation and Walker circulation over the Indo-Pacific domain are also linked to the changes in rainfall during the ENSO events, with most significant relationship during the onset phase. Keywords ENSO-monsoon relationship · Rainfall variability · Indian Ocean SST · Circulation changes
1 Introduction Indian summer monsoon rainfall (ISMR) during June–September contributes about 70–90% annual rainfall over India (Sikka 1980; Mooley and Parthasarathy 1983; Parthasarathy and Pant 1985; Varikoden and Preethi 2013) and has a large impact on the agriculture and thus the Economy of India (Ihara et al. 2007). ISMR shows large variability in different time scales and is influenced by many external players such as El Niño Southern Oscillation (ENSO, Sikka 1980; Cherchi and Navarra 2013; Nair et al. 2018) and Indian Ocean Dipole (IOD, Saji et al. 1999; Ashok et al. 2001, 2004; * Hamza Varikoden [email protected] 1
Department of Physics, Sree Krishna College, Affiliated to University of Calicut, Guruvayoor, Kerala, India
2
Indian Institute of Tropical Meteorology, Ministry of Earth Sciences, Pune 411008, India
3
CORAL, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India
Yamagata et al. 2004; Behera et al. 2006; Ummenhofer et al. 2011; Krishnaswami et al. 2014). ENSO is considered as an important tropospheric mode of climate variability (Roy et al. 2019) and one of the st
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