A Numerical Study of the Seasonal Variability of the Somali Current
Abstract
A new numerical ocean model with multiple isopycnal layers is used to model the Indian Ocean. Normal vertical modes are used for initialization and in a new open boundary formulation. A 21 year integration with the Hellerman Rosenstein wind stress is made with a 3.5 layer and a 1.5 layer version of the model. The solution with three active layers reproduces the observed general circulation and variability of the Indian Ocean, e.g., the semiannual equatorial undercurrent and Yanai wave field in the west. Seasonal changes in the Somali Current system are studied in more detail. It is found that barotropic instability is likely to cause the generation of the Great Whirl in early June. We find good agreement between the observed undercurrents and the simulations in the model. Equatorial onshore flow below the thermocline in June is associated with the disappearance of the undercurrent below the Somali current. Return of this undercurrent in the fall is caused by instability of the Great Whirl. Experiments where the duration of the summer monsoon is extended show that the initial decrease in the magnitude of the Great Whirl is due to eastward and downward energy transfer rather that due to relaxation of the wind. The model solutions indicate that baroclinic instability plays an important role in the decay of the Great Whirl. The solution with a single active layer is essentially the same for the upper layer until the late summer monsoon, when the flow becomes unstable. Different decay patterns of the whirl and associated eddies leads to different flows during the winter monsoon. (edc)
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 1990
- Accession Number
- ADA220708
Entities
People
- Tommy G. Jensen
Organizations
- Florida State University