Month-to-month variability of Indian summer monsoon rainfall in 2016: role of the Indo-Pacific climatic conditions
Indian summer monsoon (ISM) rainfall during 2016 exhibited a prominent month-to-month fluctuations over India, with below normal rainfall in June and August and above normal rainfall in July. The factors determining the month-to-month fluctuations in ISM rainfall during 2016 are investigated with main focus on the Indo-Pacific climatic anomalies. Warm sea surface temperature (SST) anomalies associated with super El Niño 2015 disappeared by early summer 2016 over the central and eastern Pacific. On the other hand, negative Indian Ocean dipole (IOD) like SST anomaly pattern over the equatorial Indian Ocean and anomalous anticyclonic circulation over the western North Pacific (WNP) are reported in summer 2016 concurrently with decaying El Niño/developing La Niña phase. Observations revealed that the low rainfall over central north India in June is due to moisture divergence caused by the westward extension of ridge corresponding to WNP anticyclone and subsidence induced by local Hadley cell partly related to negative IOD. Low level convergence of southeasterly wind from Bay of Bengal associated with weak WNP anticyclone and northwesterly wind corresponding to anticyclonic circulation over the northwest India remarkably contributed to positive rainfall in July over most of the Indian subcontinent. While reduced rainfall over the Indian subcontinent in August 2016 is associated with the anomalous moisture transport from ISM region to WNP region, in contrast to July, due to local cyclogenesis corroborated by number of tropical cyclones in the WNP. In addition to this, subsidence related to strong convection supported by cyclonic circulation over the WNP also resulted in low rainfall over the ISM region. Coupled General Circulation model sensitivity experiments confirmed that strong convective activities associated with cyclonic circulation over the WNP is primarily responsible for the observed negative ISM rainfall anomalies in August 2016. It is noted that the Indo-Western Pacific circulation anomalies in August 2016 are well predicted when the coupled model is initiated with initial conditions from end of July and beginning of August compared to May. This analysis suggests the importance of the WNP circulation in forcing strong sub-seasonal/month to month rainfall variations over India.
KeywordsIndian summer monsoon rainfall El Niño Tropical cyclones Sea surface temperature Sub-seasonal variability
We acknowledge the support from ESSO-IITM and MoES. Ferret is used for preparing manuscript figures. We thank the anonymous reviewers for the comments which helped us to improve the manuscript. Cyclone track information obtained from http://weather.unisys.com. YD is supported by the National Natural Science Foundation of China (41525019) and the State Oceanic Administration of China (GASI-IPOVAI-02). The work is also supported by State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences (LTO-OVFP NO. 1602).
- Deshpande A, Chowdary JS, Gnanaseelan C (2014) Role of thermocline–SST coupling in the evolution of IOD events and their regional impacts. Clim Dyn 1–12. https://doi.org/10.1007/s00382-013-1879-5
- IRI ENSO Forecast (2016) http://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?enso_tab=enso-iri_plume. Accessed date 12 July 2016
- Kumar V, Krishnan R (2005) On the association between the Indian summer monsoon and the tropical cyclone activity over northwest Pacific. Curr Sci 88:602–612Google Scholar
- Nitta T (1987) Convective activities in the tropical western Pacific and their impacts on the Northern Hemisphere summer circulation. J Meteor Soc Jpn 65:165–171Google Scholar
- Rajeevan M (1993) Inter-relationship between NW Pacific typhoon activity and Indian summer monsoon on inter-annual and intra-seasonal time-scales. Mausam 44:109–111Google Scholar
- Rajeevan M, Bhate J, Kale JD, Lal B (2006) A high-resolution daily gridded rainfall for the Indian region: analysis of break and active monsoon spells. Curr Sci 91:296–306Google Scholar
- Raman CRV (1955) Breaks in Indian southwest monsoon and typhoons in southwest Pacific. Curr Sci 24:219–220Google Scholar
- Roxy M, Kapoor R, Terray P, Murtugudde R, Ashok K, Goswami BN (2015) Drying of Indian sub-continent by rapid Indian Ocean warming and a weakening land-sea thermal gradient. Nat Commun 6(7423):1–10Google Scholar
- Saji NH, Goswami BN, Vinayachandran PN, Yamagata T (1999) A dipole mode in the tropical Indian Ocean. Nature 401:360–363Google Scholar