The northern Bay of Bengal plays a crucial role in regional climate, human activities, and ecological diversity, but it is unstudied by oceanographers. In 2022, the Bangladesh Oceanographic Research Institute began to address this important problem by initiating a project to collect in situ data off the coast of Cox's Bazar, Bangladesh. We report the initial results from winter 2022–23 here. High-resolution spatial measurements of ocean temperature, salinity, and horizontal velocities were made using modern sensors adapted to local boats. During this period, the coastal seas display sharp salinity-dominated density fronts, prominent temperature inversions, and partially compensated water masses. We hypothesize that these characteristics result from the stirring and mixing of cold and fresh water from local rivers, and warm and salty water from the central Bay of Bengal, creating distinct water masses on the Bangladeshi shelf. Future work aims to continue to modernize the capabilities of Bangladeshi oceanography through international collaborations, emphasizing state-of-the-art instrumentation, experimental design, and data analysis. These activities combine in a novel "cost-conscious oceanography" approach, pointing toward an innovative solution for the Global South to address data gaps in uncharted coastal seas.

Rain affects the buoyancy of the upper ocean in two ways: The freshwater flux in rain makes the water fresher and lighter, stabilizing the ocean (a negative buoyancy flux). The convective systems that produce rain are often accompanied by cold-dry-air, often called 'cold pools', and reduced short-wave radiation, which makes the water colder and heavier, destabilizing the ocean (a positive buoyancy flux). We estimate net buoyancy fluxes using in situ measurements from twenty-two moored buoys in the equatorial oceans under different rainfall categories. We find that buoyancy fluxes tend to destabilize the ocean during light rain (0.2–4 mm/hr) and stabilize the ocean during heavy rain (>4 mm/hr). Furthermore, buoyancy fluxes during rain tend to be more positive at night than during the day, with nighttime rain twice as likely to cause instability compared to daytime rain, even at the same rainfall intensity. Average buoyancy fluxes across the tropics during rain can have either sign. These findings challenge the common assumption that rainfall makes the ocean surface lighter and provide a starting point for focusing on the overall effect of precipitation on the ocean.

Tropical cyclones are among the most destructive natural disasters. However, lack of detailed observations and the simplifications inherent in operational ocean models, lead to incomplete knowledge of underlying ocean processes. Using high-fidelity large-eddy simulations and moored observations away from the storm track, we show that mutually interacting shear and convective processes, govern the evolving state of the upper ocean. Our simulation agrees well with observed sea surface temperature and sea surface salinity. Shear driven turbulence due to surface wind stress erodes stratification, deepens the ocean mixed layer and transports freshwater into the mixed layer during rain events. Concurrently, surface buoyancy loss also aids in ocean mixing via convective entrainment. The mixing efficiency and the associated eddy diffusivity shows high spatiotemporal variability throughout the water column during cyclone passage. Thus, a better insight into the upper ocean mixing mechanisms is necessary for developing improved mixing parameterizations for tropical cyclone intensity forecasts.