BoBBLE Experiment-Indian Monsoon

Large-scale weather events, such as monsoons and tropical cyclones, can now be more accurately predicted, findings from a joint India-UK research project ,BoBBLE shows.

Who all were a part of the BoBBLE?

Using a research vessel in the southern Bay of Bengal, the teams from the Indian Institute of Science, Bengaluru, the University of East Anglia (UEA) in the UK, and several Indian institutions have created a blueprint for future weather system observational experiments, critical for forecasting things such as rainfall amounts. This could mean, for example, that Asian farmers are able to determine the optimal time for planting crops and what will grow best based on expected levels of rainfall.

The project was jointly funded by the Ministry of Earth Sciences, Government of India, and the Natural Environment Research Council (NERC), UK.

The project also included researchers from Cochin University of Science and Technology, Kochi, India; the CSIR- National Institute of Oceanography, Goa; Visakhapatnam, India; the Indian National Centre for Ocean Information Services, Ministry of Earth Sciences.

What are the Findings BoBBLE?

  1. The findings, ‘Closing the sea surface mixed layer temperature budget from in situ observations alone: operation Advection during BoBBLE’, are published in Nature Scientific Reports.
  2. The findings show that oceanic processes play a crucial role in monsoon development through modulation of sea surface temperature (SST
  3. Time series of oceanographic properties, including temperature, salinity, velocity, underwater radiation and subsurface mixing, along with surface fluxes of heat, were calculated from shipboard measurements on board the RV Sindhu Sadhana in the southern Bay of Bengal during the boreal summer monsoon of 2016.
  4. The measurements were made continuously for 11 days, using a novel combination of ship-based and autonomous platforms, such as ocean gliders.
  5. The variability in tropical sea surface temperature influences large-scale ocean-atmosphere interaction processes such as the Asian monsoon, El Niño, tropical cyclones and expansion of sea ice in the Antarctic. The study in the Bay of Bengal serves as a blueprint for future observational campaigns that aim to determine the processes that affect the variability of SST and its impact on weather systems

Importance of Sea Surface Temperature:

Sea surface temperature (SST) is a fundamental driver of tropical weather systems such as monsoon rainfall and tropical cyclones.

However, understanding of the factors that control SST variability is lacking, especially during the monsoons . Here they used a ground-breaking observational approach to determine the controls on the SST variability in the southern Bay of Bengal.

It was found that the Locally measured horizontal advection and entrainment contribute more significantly than expected to SST evolution and thus oceanic variability during the observation period. These processes are poorly resolved by state-of-the-art climate models, which may contribute to poor representation of monsoon rainfall variability. The novel techniques presented in BoBBLE Findings provide a blueprint for future observational experiments to quantify the mixed layer heat budget on longer time scales and to evaluate these processes in models.

South WesT Monsoon:

The South Asian summer monsoon (June-September) provides 80% of the annual rainfall for over one billion people, many of whom depend on monsoon rains for subsistence agriculture and freshwater. It is critical to forecast accurately not only the seasonal rainfall, but also rainfall variations within the summer. Sub-seasonal “active” and “break” phases can last weeks, resulting in floods and droughts across broad areas of South Asia.

Air-sea interactions are key to understanding and predicting monsoon behaviour. Ocean surface temperatures in the Bay of Bengal, east of India, remain very warm (above 28 C) throughout the summer. Evaporation from the Bay provides moisture and energy to monsoon depressions that form over the Bay and bring substantial rain to India. It is not understood how the Bay remains warm despite losing energy to these systems. Ocean temperature and salinity variations across the Bay are known to drive changes in rainfall over the Bay and surrounding land, but it is not clear how these arise or how they are maintained.

Important Topics Prelims 2020

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