Investigation of Internal Tides Variability in the Andaman Sea: Observations and Simulations

The Andaman Sea in the Indian Ocean is known for the presence of large-amplitude Internal waves (IW). Internal tides (IT) are IW of tidal frequency whose temporal variability is unknown in this region. Therefore, we used in-situ observations collected at (10.5 degrees N, 90 degrees E) from March 2017 to February 2018. The analysis shows that the kinetic energy of semidiurnal IT is dominant to that of diurnal IT by a factor of 4-5. The ellipticity of both semidiurnal and diurnal motions is dominated by rectilinear zonal flow, indicating generation at the slopes of the Andaman and Nicobar islands. Maximum isopycnal displacement reached 46 m for semidiurnal IT. The semidiurnal IT displayed significant seasonal variability-Stronger in summer and autumn but weaker in spring and winter, whereas the diurnal IT are relatively stronger in summer and winter. Furthermore, salinity plays a dominant role in controlling the near-surface stratification, whereas the temperature variations control the subsurface stratification. This led to the formation of a strong double pycnocline during autumn and winter. Baroclinic coherent semidiurnal (diurnal) variance accounts for 49% (27%) of the semidiurnal (diurnal) motions. Model simulations carried out for March, June, September, and December of 2017 using the Massachusetts Institute of Technology General Circulation Model showed significant seasonal variability in the generation and dissipation of IT. The isopycnal displacement near the generation sites is about 88 m. The experiments suggest that the presence of the Andaman Nicobar Ridge contributes nearly 89% to the total IT generation.