Abstract
Abstract : With a focus on the Bay of Bengal, models ranging from a 1/12.5 global ocean model to a 1/4 regional Indian Ocean model to a 2 km local high-resolution coupled model are used to simulate salinity exchanges in the Indian Ocean. Global Hybrid Coordinate Ocean Model simulations show a surprisingly large persistent flow of high-salinity water from the equatorial Indian Ocean into the Bay of Bengal during the northeast monsoon, although it is weaker than during the southwest monsoon. On average, salt is transported into the Bay of Bengal between 83E and 95E, and low-salinity water flows southward near the east coast of Sri Lanka and east of 95E. The Regional Ocean Modeling System shows that knowledge of river input of freshwater is essential for modeling surface salinities correctly in the Bay of Bengal. High-resolution coupled model simulations are in agreement with recent observations and show that a strong subsurface current with a speed of about 1 m s -1 intrudes into the Bay of Bengal beneath southward-flowing low-salinity water during the northeast monsoon. The subsurface high-salinity water, which originates in the northern Arabian Sea, spreads northward into the Bay of Bengal and downward along constant density surfaces. North of 10N, the model simulation implies that mixing takes place on density surfaces at depths of 100 -150 m after advection of cold, low-salinity water from the north, and subsequent stirring of the two water masses. Vertical diffusion plays an insignificant role in this mixing.
Highlights
Realistic numerical models of the atmosphere-ocean system are useful for helping to interpret field observations by relating the data collected to water masses and currents on a regional scale
Results from a 20-Year Global Hybrid Coordinate Ocean Model (HYCOM) Reanalysis A monthly mean climatology was computed from the 20-year HYCOM integration
The models show that salinity exchanges between the equa
Summary
Realistic numerical models of the atmosphere-ocean system are useful for helping to interpret field observations by relating the data collected to water masses and currents on a regional scale. The tropical ocean adjusts much faster to such changes than the mid-latitude ocean due to much larger planetary wave (i.e., Rossby wave) speeds in the tropics This is the case for the special class of equatorial Kelvin waves and equatorial Rossby waves that propagate only along the equator in the so-called equatorial wave guide (Matsuno, 1966). They play a vital role in the onset of the El Niño-Southern Oscillation in the Pacific, and are thought to play a key role in intraseasonal oscillations in the Indian Ocean. The latter is an important link in the global circulation as it connects the Pacific Ocean to the Indian Ocean via the Indonesian Throughflow (e.g., Qiu et al, 1999; Shinoda et al, 2012)
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