The Indian summer monsoon brings torrential rains to Southeast Asia from June through September every year in a weather event with massive impacts on local economics, infrastructure, and culture. In summer, winds from the southwest carry moisture from the Indian Ocean and deposit it over the Indian subcontinent. Around October, the winds reverse direction, and only certain regions receive the remaining moisture.
The topography of the subcontinent further contributes to the intensity of the monsoon, with the Himalayas and the Western Ghats acting as barriers that trap severe weather above India. Despite its seasonality, the timing, duration, and intensity of the Indian Summer Monsoon vary widely, and scientists are keen to improve modeling and prediction methods to account for this kind of variability.
Using observations from an instrument called the Atmospheric Infrared Sounder (AIRS) aboard NASA’s Aqua satellite, Raju et al. evaluated how changes in temperature and moisture with respect to altitude influence monsoon development. They used the data to model monsoon characteristics, including precipitation, easterly wind shear, low-level moisture distribution, and the temperature of the troposphere (the lowest layer of Earth’s atmosphere).
By combining observations and a regional model, the team was able to more accurately forecast patterns of precipitation across the region. The forecast monsoon features are highly correlated with observations, indicating their potential value for future predictions of the Indian summer monsoon. The AIRS data may be the key to more realistic models of temperature and moisture processes that drive monsoon development and behavior. Seasonal forecast improvements would have tremendous implications for lives and livelihoods throughout the region, especially during the extremes (drought or flood). (Journal of Geophysical Research: Atmospheres, doi:10.1002/2014JD023024, 2015)
—Lily Strelich, Freelance Writer
Citation: Strelich, L. (2015), Improving Indian summer monsoon prediction, Eos, 96, doi:10.1029/2015EO039685. Published on 20 November 2015.