The BoBBLE cruise has departed today, following a departure ceremony led by Dr M Rajeevan, secretary for the Indian Ministry of Earth Sciences. The cruise sets sail for the southern Bay of Bengal, where scientists on board will monitor the ocean and atmospheric conditions for a month to better understand how changes in the ocean influence the monsoon rainfall.
The expedition takes place aboard the Indian ship, ORV Sindhu Sadhana, from which we will launch seven Seagliders (ocean robots that “fly” underwater) to take high-resolution measurements of the conditions in the Bay of Bengal, along a 400 km section in the southern part of the Bay, at 8°N, between 85 and 90°E. Observations will also be made from the ship itself, and by releasing nine customised Argo floats (simpler ocean robot, that drift passively with the currents) to take measurements over an even wider region. This research project is the first time that such detailed ocean measurements will be taken during the difficult weather conditions that prevail during the monsoon.
We are interested in measuring the interaction between the ocean conditions and the atmosphere, in particular how ocean processes change the surface temperature and thus the amount of heat available to drive the storm systems that bring rainfall over India. It has been suggested that changes in the surface conditions over the Bay of Bengal influence the Indian monsoon rainfall, but it is not clear what drives the changes in the ocean. One theory is the interaction between warm salty water from the Arabian Sea and colder, fresher water from the northern part of the Bay, where rainfall and river input reduce the saltiness of the water to around half the normal amount for seawater. It is not known how and where these different currents of water mix, especially during the monsoon when observations have not previously been possible. Some of the Seagliders are equipped with “microstructure probes” that can take direct measurements of how these water masses are mixing vertically, while the combination of all the measurements across the region will help us understand how the ocean currents transport heat and salt around this part of the Bay of Bengal.
Scientists from the UK and India will use the understanding we gain from the ocean and atmospheric observations made during the field campaign to help improve the models that are used to predict Indian monsoon rainfall. We will test the forecasts made during the monsoon and seek to improve how the models represent the ocean processes we observe. Forecasting the monsoon will always be difficult due to the complexities of the system, but hugely important to the Indian people and economy. We hope to be able to make a substantial contribution to improving these forecasts over the 5-year lifetime of the project.