Investigation of coastal trapped waves on the southern continental shelf of Caspian Sea of Babolsar, off Mazandaran

The Caspian Sea, as the largest inland water body on the Earth has a unique marine environment and is of great importance for the world and the lateral countries around it. The continental shelf is one of the most important and diverse ecosystems economically and ecologically. There is no doubt that coastal trapped waves are a major feature of most shallow shelves. Coastal trapped waves can make a significant contribution to the observed variability of sea level and currents on the shelf and it is essential to include them in a discussion of the coastal ocean. One of the common tools for investigating coastal trapped waves is numerical modeling. Brink model is the set of Matlab mfiles can be used to calculate coastal trapped wave modal structures and dispersion curves under very general circumstances. A complex frequency is allowed, so that instability and damping can be accounted for directly. According to previous investigation about currents on continental shelf off Babolsar, alongshore currents were uniform across the depth and were dominated by low frequencies less than 0.33 cycle per day with peak energy at 7-9 days periods. The results showed a low relationship between low frequency dominated alongshore currents and local wind forcing and raised the hypotheses of the existence of west to east traveling coastal trapped waves along the southern coast of the Caspian Sea [1]. In this paper, existence of trapped waves which produce currents on continental shelf off Babolsar are investigated by the Brink model. Therefore, comparison between results of model and field measurements is performed to prove this hypothesis. Also, the type and characteristics of trapped waves in summer and winter on Babolsar shelf are identified by principle formulas.