Research Highlights

doi:10.1038/nindia.2014.146 Published online 30 October 2014

Solar radiation shapes Indian monsoon rainfall

By using computer-based model, researchers have gained new insights into how solar radiation influences the Indian summer monsoon rainfall for long periods spanning decades1. This model is potentially useful for predicting Indian summer monsoon rainfall.

The Sun’s energy creates a temperature difference between the subcontinent and the ocean. This generates water vapour, which moves inland and mixes with clouds, producing rain under suitable conditions. Previous studies had shown that the Sun’s radiation could influence Indian monsoon rainfall. However, it is not well understood how Sun’s energy output shapes summer rainfall over time scales of years and even decades.

To better understand the link between solar radiation and Indian summer monsoon rainfall, the researchers developed a computer model that evaluated how solar activities such as sunspots and coronal holes influence the mixing ratios of cloud and rain water. The mixing ratios of cloud and rain water are known to affect rainfall. In addition, the model also incorporated physical parameters such as acceleration due to gravity and temperature, which also influence rainfall.

The researchers then matched the model-generated rainfall data with actual data for summer monsoon rainfall recorded between the years 1871 and 2005. They found that heightened solar activities such as sunspots and coronal holes could increase solar radiation, enhancing rainfall.

The study results reveal that variations in the Sun’s radiation output causes variations in the ocean-generated atmospheric water vapour, which in turn influences the cloud and rain water mixing ratios. The anomalies in computed rainfall data matched 90% of those of the observed real rainfall data and rainfall variations that caused floods and droughts.

“An increase of 0.1% of solar radiation could substantially increase atmospheric water vapour, suggesting that solar radiation has a strong influence on the Indian monsoon rainfall,” says K. M. Hiremath, a senior author of the study.

The authors of this work are from: Indian Institute of Astrophysics, Bengaluru, India and Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.


References

1. Hiremath, K. M. et al. Indian summer monsoon rainfall: dancing with the tunes of the sun. New Astron. 35, 8-19 (2015)