Northward propagating coherent signals of sea surface temperature (SST), heat, momentum and moisture fluxes, outgoing longwave radiation (OLR) and rainfall anomalies have been long observed in meteorological studies of summer monsoons in the Bay of Bengal (BOB) and Southern Indian Ocean. These disturbances also have a less-pronounced westward propagating component over the Indian subcontinent, with horizontal scale larger than the Indian continent itself. They are a part of the family of Intra-Seasonal Oscillations (ISO) signals, dubbed Monsoon Intra-Seasonal Oscillations (MISO), and have received wide attention because of their close correlation with the active and break phases of monsoons.
Reliable predictions of the initiation, propagation, strength, and variability of MISO constitute building blocks of monsoon forecasting, which are crucial for ensuring the socioeconomic wellbeing and safety of nearly one billion inhabitants of the Indian subcontinent. MISO are sub-seasonal weather phenomena that originate in the tropics, propagate predominantly northward over the Bay of Bengal (BOB) and then move westward over the Indian landmass. Active and break phases of monsoons are directly correlated with MISO, but significant biases and errors in current forecasts have been a bane for environmental planning beyond several weeks in advance. Mounting evidence suggests that accurate accounting of air-sea coupling is imperative for skillful forecasting of MISO and attendant outcomes such as rainfall, yet our lack of understanding of thermodynamic and physical processes, both on the ocean and atmospheric sides, has stymied the progress of forecast improvements. MISOs are a meld of multiscale physical processes working symbiotically to produce organized, migrating rain bands separated by periods of clear sky.
This project seeks to study critical science questions underlying MISO dynamics. Of particular interest are the physical mechanisms responsible for heat, momentum and mass transfer across the air-sea interface, feedbacks between atmospheric and oceanic boundary layers, lead-lag relationships between the sea-surface temperature (SST), net heat flux and precipitation, as well as sustaining and dissolving MISO convection. Collectively, a suite of high-end atmospheric and oceanic instrumentation is to be deployed in the Indian Ocean, on the land over multiple countries, aboard research vessels and on an aircraft to collect data of high granularity. Ultra-high resolution coupled numerical simulations are to be used to guide field experimental designs and data interpretation. Novel autonomous measurement platforms and large eddy simulation (LES) technologies are to be developed to study MISO relevant air-sea processes. Satellite and reanalysis products are to be used to augment in situ data, allowing integration of observations across sub-meso to seasonal scales. In unison, the project will contribute to improved forecasts of MISO, and Monsoons in general, via discovery of physical mechanisms, understanding their linkages, development of model-relevant parameterizations, and providing a robust dataset for modelers. Collaboration with government agencies from the US and partnering countries (Sri Lanka, Maldives, Singapore and Seychelles) will help transition research to forecasting products. The project includes capacity building of partnering countries.