Study of internal wave characteristics off northwest Bay of Bengal using synthetic aperture radar

Abstract

Internal solitary waves (IWs) in the northwest Bay of Bengal were studied using ENVISAT ASAR imageries. Simultaneous in situ observations were also carried out to study the characteristics of the internal waves. Internal wave features have often been observed over the ocean area between 18.5°–19.5° N and 84.5°–85.5° E. The direction of propagation of IWs is generally toward the coast with wavelengths ranging from 0.4 to 1.1 km. The phase speeds of the IWs vary from 0.12 to 1.3 m/s. Internal wave amplitudes computed using Korteweg and de Vries model show good agreement with in situ data. Based on their direction of propagation and time series analysis, IWs generated were found to be of tidal forcing origin over local topographic features. IWs of different types like wave packets or wave trains and single solitons of weak manifestations were observed depending on the phase and the tidal amplitude as well as the stratification of the ocean, which in turn vary due to the dynamic and complex nature of Bay of Bengal, as it experiences strong monsoon winds and low pressure systems with calm weather in between them. The internal waves are often observed during non-monsoon period over this region. During monsoon period, continuous vertical mixing takes place due to strong winds causing unfavorable conditions for IW formation and so the observation of IWs during monsoons is rather rare.