Dynamics of counter wind current along the south Sri Lanka coast during the Southwest Monsoon

• Published in: Ocean dynamics Vol. 71; no. 11-12; pp. 1051 - 1067
• Main Authors: Wickramage, C. H., Wang, Weiqiang, Arulananthan, K., Jayathilake, Ruchira
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-12-2021; Springer Nature B.V
• Subjects: Atmospheric Sciences; Baroclinic flow; Barotropic instability; Barotropic mode; Bends; Climatology; Coastal currents; Dynamics; Earth and Environmental Science; Earth Sciences; Flow stability; Fluid- and Aerodynamics; Geophysics/Geodesy; Interannual variability; Intraseasonal oscillation; Monitoring/Environmental Analysis; Monsoons; Ocean circulation; Oceanography; Planetary waves; Rossby waves; Southwest monsoon; Stability analysis; Summer; Summer monsoon; Upwelling; Velocity distribution; Velocity profiles; Wind; Wind currents; Wind speed; Sri Lanka; Boreal summer intra-seasonal oscillation; South Sri Lanka coastal current; Southwest monsoon current; Sri Lanka dome
• ISSN: 1616-7341; 1616-7228
• DOI: 10.1007/s10236-021-01477-6

Shipboard velocity profiles collected in July 2018 are used to study coastal current in the south of Sri Lanka during the summer monsoon. The observations reveal that there is a narrow (~ 50 km wide) westward coastal current against the summer monsoon, separated the eastward southwest monsoon current (SMC) from the island of Sri Lanka. However, the climatological south Sri Lanka coastal current (SSLCC) is eastward following the direction of the SMC. The deviations between the observations and climatology of the SSLCC suggest its significant interannual variability. The dynamics of the westward SSLCC and its impact factors are thus focused on in this study. The results indicate that two main processes are responsible. First, the boreal summer intraseasonal oscillation (BSISO) plays an important role in the presence of westward SSLCC. The BSISO signal intensifies the wind strength east and south of Sri Lanka, reinforces the east India coastal current (EICC), and bends the SMC favoring occurrence of the westward SSLCC. Second, the upwelling Rossby wave signal propagates to Sri Lanka but stops at 82°E, which favors the Sri Lanka Dome developing. As the western flank of the SLD, the strengthened EICC flows southward and turns to west resulting in the westward SSLCC. Accordingly, the energy conversions by baroclinic and barotropic instability between mean flow and eddy are analyzed for both the westward and eastward SSLCC.