Coastal Kelvin waves and dynamics of Gulf of Aden eddies

- In addition to Rossby Waves and oceanic instabilities the coastal Kelvin waves are also important for Gulf of Aden Eddies.
- Coastal Kelvin waves along coast of Arabia determine the timing and amplitudes of Gulf of Aden Eddies.
- Within the Gulf of Aden the circulation is not only governed by the meso-scale eddies but also by the coastal Kelvin waves.
- The model results and tide-gauge observations from Salala and Aden support the role of coastal Kelvin waves in Gulf of Aden.

The Gulf of Aden (GA) is a small semi-enclosed oceanic region between the Red Sea and the western Arabian Sea. The GA is characterised with westward propagating cyclonic and anti-cyclonic eddies throughout the year. The genesis and propagation of these eddies into the GA have been the focus of several studies which concluded that oceanic instabilities (both barotropic and baroclinic) as well as the Rossby waves from the Arabian Sea are the responsible mechanisms for the presence and maintenance of these eddies. Using a high-resolution (~11 km) reduced gravity hydrodynamic layered model with controlled lateral boundary conditions at the three sides of the GA here we show yet another factor, the coastally propagating Kelvin waves along the coastal Arabia (coasts of Oman and Yemen), is also critically important in setting up a favourable condition for the oceanic instabilities and sustenance of meso-scale eddies in the GA. These Kelvin waves at both seasonal and intra-seasonal time scales are found play an important role in the timing and amplitudes of eddies observed in the GA.