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Scientists study waves to predict Indian monsoons

By AMRITA BALRAM | March 5, 2020

Harindra Fernando gave a talk titled “Monsoon Intraseasonal Oscillations in Equatorial Atmosphere and Oceans” on Feb. 28 in Hodson Hall. The talk was sponsored by the Center for Environmental and Applied Fluid Mechanics as part of their weekly seminar series and hosted by Rui Ni, an assistant professor of Mechanical Engineering at Hopkins. 

Fernando is currently a professor of Engineering and Geosciences at the University of Notre Dame. In 1983 he completed his doctorate in Geophysical Fluid Dynamics at Hopkins and worked in a lab in the basement of Olin Hall. He began the talk by reminiscing about his time at Hopkins, sharing photos of people he worked with and what the lab looked like 37 years ago. 

The seminar primarily focused on the Indian summer monsoons and how they can be predicted. Monsoons are characterized by intraseasonal oscillations, or long term in-between season oscillations that consist of periods of both active rain flow and stagnant breaks. 

Oscillation periods of active rainfall and then a break phase with no rainfall are extremely common in the Indian Ocean and have been measured to be about 32-60 days long. The oscillations are collectively called Monsoon Intraseasonal Oscillations (MISO). The MISO ranges from the equatorial Indian Ocean to the Bay of Bengal. 

Fernando used moving satellite images to depict what happens during monsoon periods. 

“These are large scale planetary waves that are 10,000 kilometers long. They start by propagating into the Bay of Bengal,” Fernando said. “A pressure gradient breaks the planetary wave and part of it goes to the northern Bay of Bengal and the other part of it goes to the Pacific Ocean.” 

He explained that depending on the season and its corresponding weather, the atmosphere and the ocean move in different ways. In the summer, when the ocean is relatively colder than its surrounding land mass, the monsoon travels in a reverse direction. 

The changes in the atmosphere correspond to changes in the movement of ocean currents. The current in the Indian Ocean flows north from the Arabian Sea to the Bay of Bengal in the summer and westward toward the Bay of Bengal in the winter, splitting into westward and northward branches. 

As a researcher, Fernando has conducted several field experiments to predict monsoons. In 2012, the U.S. Office of Naval Research sponsored a program to study the atmosphere and ocean together with the goal of looking for MISO events in the Indian Ocean. The program was the result of collaboration between several countries including Sri Lanka, India and the United States. 

Six cruise ships were deployed to drop six moorings in different ocean locations to collect measurements over 5,000 kilometers of predicted monsoon waves. The moorings took several measurements and allowed researchers to collect abundant data about the climate and environment under the water. After 697 days of collecting data, Fernando and his group analyzed the data with a velocity spectrum in order to identify oscillations. This program helped determine the size and speed of many of the waves in the region. 

One of the program initiatives, MISO-BOB, began in 2018 and will continue until 2022. Focused solely on MISO events, this experiment used an aircraft to move through the cloud system and a research ship to cover the ocean surface. Fernando noted how difficult it was to convince the collaborating nations to agree to let the study’s aircraft invade their airspace.

“We had to have the Ministry of Foreign Affairs, the Ministry of Defense and the Ministry of Airforce and the Navy, as well as the cabinet’s approval in order to operate in places,” Fernando said. 

The United States granted the use of the 53rd division aircraft for two weeks. The aircraft made measurements of wind speed, rain rate, vertical profiles and radar by flying through monsoon clouds every other day for the duration of the two weeks. The research programs uncovered unknown aspects of MISO dynamics and observed that the ocean was heavily controlled by MISO due to multiple air and sea interactions.

During his talk, Fernando outlined many applications for research on monsoons. He shared that today, the Indian population receives freshwater solely from them. Oscillation periods of intense rain and intense drought, such as El Niño, are also often the cause of natural disasters. 

Fernando emphasized that the movement of the Indian Ocean affects all bodies of water, meaning it has the potential to impact the whole world. Monsoon predictions in the Indian Ocean also have several military defense applications, as the Indian Ocean is home to several powerful military fleets, including the U.S. Army’s fifth fleet.

Fernando hopes to continue the research program in order to better understand how water and air interactions affect the wave patterns in the region. At the end of his talk, he emphasized that projects like his require constant collaboration between many researchers, institutions and even countries. 

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