Scientists from the U.S., India, and Sri Lanka have set sail aboard the Scripps research vessel Roger Revelle as part of a five-year multinational effort to understand the South Asian monsoon, a defining torrential rain that is essential to the economic life of the countries that ring the Bay of Bengal.
The body of water is home to a complex suite of ocean dynamics that significantly control monsoons but that to date have been seldom studied by oceanographers.
“Monsoonal rains result in hundreds, sometimes thousands, of unnecessary deaths in part because they’re poorly predicted,” said Scripps physical oceanographer Jennifer Mackinnon, one of the scientists from nine U.S. research centers who are taking part in the Air-Sea Interaction Research Initiative (ASIRI).
Reliable forecasts of this intriguing weather pattern require a deeper understanding of the ocean-atmosphere dynamics that influence monsoon formation. As with hurricanes, monsoons draw energy from warm ocean water. In the Bay of Bengal, which borders the coastlines of India, Sri Lanka, Bangladesh, and several other countries, heat contained in the upper ocean can be effectively isolated from the atmosphere by a layer of fresh water on the ocean surface. This layer is created by flows from the Ganges, Irrawaddy, and several other rivers that originate thousands of feet above sea level, as well as intense precipitation over the basin associated with the monsoon. The resulting vertical structure of salinity and temperature found in the Bay of Bengal is further modified by a series of dynamic processes such as eddies, fronts, internal waves, and turbulent mixing. Their interplay results in unique oceanographic features that create ocean-atmosphere interactions that are markedly different than those found elsewhere.
The weather set in motion by the monsoon has widespread effects over time, eventually reaching places as far away as the United States.
ASIRI researcher Amit Tandon, a physical oceanographer at the University of Massachusetts Dartmouth said the project, which runs through 2017, is achieving several firsts such as the first coordination of at-sea operations between a U.S. and an Indian research vessel (R/V Sagar Nidhi). Scripps physical oceanographer Drew Lucas and Oregon State physical oceanographer Emily Shroyer led the cruise aboard R/V Roger Revelle. Preparations for the fieldwork began nearly three years before the first leg, led by Office of Naval Research (ONR) Program Officer Terri Paluszkiewicz, a small steering group of scientists from the United States and India and counterparts at the Indian Ministry of Earth Science, and other agencies. ONR funded the U.S. portion of the study.
The Indian component of the project, funded by the Ministry of Earth Sciences, New Delhi, aims to understand the physics of the Bay of Bengal. Debasis Sengupta, a physical oceanographer with the Indian Institute of Science, is the lead of the Ocean Mixing and Monsoon Experiment.
“The north Bay of Bengal receives about four meters of net freshwater from river runoff and rain each year,” said Sengupta. “The strong near-surface salinity stratification has profound influence on ocean thermodynamics and the interaction of the ocean with the monsoon atmosphere. Our partnership with ASIRI scientists will not only help to learn more about the fascinating physics of this ocean basin, and also help train early-career Indian scientists in high-resolution ocean observations and modeling. We hope that the collaborative effort will lead to better parameterization of upper ocean processes and eventually to improved models for monsoon prediction.”
“This visit of this U.S. oceanographic research ship to India is an important moment in the history of scientific partnership between our two countries,” said Frank Herr, head of the Ocean Battlespace Sensing Department at the Office of Naval Research. “We hope to grow lasting scientific cooperation between our nations and acquire the knowledge to better forecast the initiation of the annual monsoons. We also look forward to the scientific discoveries and innovation that will come from the joint work of these academic scientists.”
On June 14, Acting Consul General Nicholas Manring from the U.S. Consulate General, Chennai welcomed scientists on board R/V Roger Revelle and led a brief ceremony dockside. The Chennai port call included appearances by U.S. consular officials and Indian dignitaries.
“Ship visits represent an important opportunity to promote cooperation and enhance peace and stability in the Asia-Pacific region and they demonstrate the United States' commitment to regional partners while also fostering our growing bilateral relationship with India,” said Manring. “We deeply value our scientific partnerships with India and believe that strong relationships between our research institutions are integral to promoting peace, security, and stability in the Indian Ocean region.”
A Scripps research vessel last visited India in 2007, as part of a joint US-Indian study in the Arabian Sea.
The cruises undertaken this summer are part of a series in which scientists from both countries, as well as Sri Lanka, will seek to understand the ocean dynamics that influence monsoons in South Asia. Tandon said the most intensive field studies will take place next year. By the end of the project, R/V Roger Revelle might leave and return to Indian ports as many as four more times.
Tandon and Mackinnon added that training of early-career Indian scientists by ASIRI scientists is another component of the project solidifying the oceanographic research relationship between the two countries. A workshop on upper ocean processes began July 9 at the Indian Institute of Science Bangalore.
“I’m hoping with this, we really open the floodgates for collaboration among scientists in both countries,” said Tandon.
– Robert Monroe