Sri Lanka Dome Research Articles

Surface circulation and upwelling patterns around Sri Lanka

Abstract. Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean, with the Arabian Sea on its western side and the Bay of Bengal on its eastern side, and experiences bi-annually reversing monsoon winds. Aggregations of blue whale (Balaenoptera musculus) have been observed along the southern coast of Sri Lanka during the northeast (NE) monsoon, when satellite imagery indicates lower productivity in the surface waters. This study explored elements of the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka using satellite imagery and numerical simulations using the Regional Ocean Modelling System (ROMS). The model was run for 3 years to examine the seasonal and shorter-term (~10 days) variability. The results reproduced correctly the reversing current system, between the Equator and Sri Lanka, in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the southwest (SW) monsoon transporting 11.5 Sv (mean over 2010–2012) and the westward flowing Northeast Monsoon Current (NMC) transporting 9.6 Sv during the NE monsoon, respectively. A recirculation feature located to the east of Sri Lanka during the SW monsoon, the Sri Lanka Dome, is shown to result from the interaction between the SMC and the island of Sri Lanka. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the southern coast. During the SW monsoon, the island deflects the eastward flowing SMC southward, whilst along the eastern coast, the southward flow results from the Sri Lanka Dome recirculation. The major upwelling region, during both monsoon periods, is located along the southern coast, resulting from southward flow converging along the southern coast and subsequent divergence associated with the offshore transport of water. Higher surface chlorophyll concentrations were observed during the SW monsoon. The location of the flow convergence and hence the upwelling centre was dependent on the relative strengths of wind-driven flow along the eastern and western coasts: during the SW (NE) monsoon, the flow along the western (eastern) coast was stronger, migrating the upwelling centre to the east (west).

Biological response of the sea around Sri Lanka to summer monsoon

Chlorophyll‐a concentration (chl a) maps derived from the Ocean Color Monitor (OCM) on board Indian Remote Sensing Satellite (IRS‐P4) and Seaviewing Wide field of View sensor (SeaWiFS) show increased chl a in the waters around Sri Lanka during summer monsoon. Physical processes that can lead to the phytoplankton bloom are investigated using upper ocean temperature profiles and satellite derived winds, sea surface temperature (SST) and sea level anomalies (SLA). There is a chl a bloom attached to the southern coast of Sri Lanka accompanied by cool SST, low SLA and upsloping of isotherms towards the coast. Coastal upwelling driven by monsoon winds is identified as the physical mechanism causing nutrient enrichment in the surface layer. The Southwest Monsoon Current (SMC) which flows eastward south of Sri Lanka and then into the Bay of Bengal advects the upwelled water eastward along its path. The chl a rich waters from the Indian coast also advects along with the SMC towards Sri Lanka. East of Sri Lanka the open ocean upwelling associated with the Sri Lanka Dome is also found to be an important process that upwell nutrients.

Monsoon Response of the Sea around Sri Lanka: Generation of Thermal Domesand Anticyclonic Vortices

Abstract Results from an ocean general circulation model are used to study the response of the oceanic region surrounding Sri Lanka to monsoonal winds. East of Sri Lanka, a cold dome (Sri Lanka dome, SLD) develops during the southwest monsoon (SWM) in response to cyclonic curl in the local wind field. The dome decays after September due to the arrival of a long Rossby wave, associated with the reflection of the spring Wyrtki jet at the eastern boundary of the ocean. East of the SLD an anticyclonic eddy exists that is in intermediate geostrophic (IG) balance. North of Sri Lanka a cold dome (Bay of Bengal dome) develops after the SWM associated with a cyclonic gyre forced by Ekman pumping. The source of cold water of the Bay of Bengal dome is traced back to the SLD and upwelling zone along the east coast of India. South of Sri Lanka a major part of the Southwest Monsoon Current (SMC) turns northeastward and flows into the Bay of Bengal. The part that flows eastward terminates at progressively western longit...