Seasonal Monsoon Variations in Surface Currents in the Gulf of Thailand Revealed by High Frequency Radar

Surface currents in coastal waters can be mapped with high frequency radar (HF radar). In this study, month-long surface vector current data from the Upper Gulf, Central Gulf and Lower Gulf of Thailand (UGOT, CGOT, and LGOT, respectively) were analyzed and compared during a northeast (24 January 22 February 2015) and southwest (25 May 23 June 2015) monsoon to investigate seasonal patterns. Temporal averaging of surface currents at UGOT indicated no circulation pattern differences between seasons. Area averaging revealed that flow was strongly tidally influenced; however, a tidal influence was observed during the southwest monsoon at CGOT and LGOT. During the northeast and southwest monsoons at both CGOT and LGOT, residual current flowed in the northwest and northeast directions, respectively. Tidal ellipse analysis of diurnal (K1 and O1) and semi-diurnal (M2 and S2) tidal components demonstrated that the magnitude and rotation of each component differed from site to site and season to season. Overall, this study revealed that surface current patterns in the Gulf of Thailand changed from one season to another, provided evidence for changes in spring and neap tide signal (during monsoon events), and the possible existence of anti-cyclonic eddies (driven by monsoon events).