Narrow Results

Tropical cyclones are considered as one of the most intense case of air–sea interaction processes. Tropical cyclones receive energy from the upper ocean surface through exchanges of momentum and enthalpy fluxes. Ocean wind-generated surface gravity waves play a vital role in modulating the ocean surface conditions and momentum fluxes. Therefore, understanding of the ocean surface waves response during the passage of tropical cyclones would be beneficial for improved storm prediction. In the present study, an attempt has been made to quantify the characteristic of ocean surface waves during the passage of tropical cyclones. Here, we use the 27 years (1993–2019) of global wave reanalysis data sets and tropical cyclone track to develop composite maps of ocean surface waves with regard to the tropical cyclone intensity (maximum sustained wind speed) translation speed over the Bay of Bengal basin. Results suggest that transitional speed plays a vital role for the symmetric and antisymmetric pattern of the ocean surface waves. Findings from the present study are useful for the validation and improvement of state-of-the-art coupled-wave atmosphere models.

In order to simulate the storm surge in the Bay of Bengal (BoB), the Wind-Wave-Water level coupling model is introduced in this paper. In this study, an Atmosphere-Wave-Hydrodynamic real-time coupled model (WRF + SWAN + FVCOM) is established using the Model Coupling Toolkit (MCT) coupler, and by this coupled model, the storm surge during tropical storms considering the wave radiation stress was calculated. The cyclone path, wave height, wind speed and water level of this coupled model was verified using the typhoon path of JTWC, the wave height and wind data of Jason satellite data and the site-measured water level data of several nearshore stations. Using this model, the storm surge caused by 38 Cyclones affecting the BoB from 1987 to 2018 was calculated, and the distribution of BoB extreme storm-surge of various return years was analyzed according to the calculation results. This paper also discussed the influence of wave radiation stress on storm surge for some severe cyclones. This study can guide the disaster prevention and engineering design of nearshore projects.

The upper ocean mixing in the Bay of Bengal (BoB) gets substantial influence from the local winds, huge fresh water influx and tidal forcing that makes the mixing more complex and dynamic. This study aims to understand the role of tidal forcing on upper ocean mixing in the BoB and how this mixing process changes in presence of river fresh water. Moreover, it is also seen that how this tidal forcing modulates the air-sea interactions in the region. The analysis includes three high resolution (1/12°) Regional Ocean Modelling System (ROMS) simulations, a control run, a tide run and a river-tide run. In the tide forcing simulations, the tidal components included are M2, S2, N2, K2, K1, O1, P1, Q1, Mf and Mm. Again, the river-tide simulation additionally has the discharge from the major rivers (Ganges, Brahmaputra, Irrawaddy, Godavari, Krishna, Mahanadi and Subarnarekha) in the region. The analyses show that the tidal buoyancy deepens the mixed layer increasing the integrated upper ocean temperature, while the surface temperature reduces. The upper ocean temperature profile further reduces in the tidal vertical mixing process in presence of river fresh water. The tidal mixing increases the surface salinity, whereas the addition of low saline river discharge largely reduces the surface and subsurface salinity. The warmer upper ocean layers in the tidal forcing simulation radiates more surface longwave, sensible and latent surface heat fluxes over the region. Therefore, the study shows that the tidal forcing has major influence in the upper ocean mixing as well as the air-sea fluxes over the BoB.