A Study On The Hydrographic And Circulation Characteristics Of The Upper Layer In The Andaman Sea Based On In-situ And Satellite Data

The Andaman Sea,situated in the northeastern Indian Ocean,is connected to the South China Sea through the Malacca Strait in the south.The region has complex topography and is significantly influenced by monsoons,and various physical processes such as equatorial Kelvin waves,internal tides,and solitary internal waves coexist,resulting in a complex dynamic system.Research on the oceanography of the Andaman Sea is crucial for understanding material and energy exchange on the tropical Indian Ocean basin scale,multi-scale circulation evolution,and their underlying controlling mechanisms.Compared to other parts of the Indian Ocean,research on the Andaman Sea is limited due to a lack of observational data.Therefore,this study combines satellite remote sensing data,in-situ measurements of temperature and salinity,and long-term current data to analyze the hydrological and circulation characteristics of the Andaman Sea and investigate the underlying dynamic mechanisms.The analysis reveals that the Andaman Sea has relatively high sea surface temperatures,generally exceeding 28°C.Surface temperatures exhibit a higher trend in spring and lower in winter.The sea’s surface salinity values are low,with most areas having surface salinity below 32 psu.During summer,there is a strong intrusion of low-salinity water in the northern region.In winter,the temperature in the upper200 m layer ranged from 12–31°C,and salinity ranged from 32–35 psu.The thermocline primarily occurred at depths of 70–200 m,while the halocline appeared at50–150 m.The circulation field of the Andaman Sea exhibits significant seasonal variation.During the late northeast monsoon(January–March),the circulation field is dominated by southward currents under the control of the monsoon.During the monsoon transition periods(April–May and October–November),the circulation field is mainly influenced by equatorial waves,with northward currents prevailing.In the southwest monsoon period(June–September),the intrusion of low-salinity water from the Bay of Bengal and the input of terrestrial runoff occur in the northern Andaman Sea,with the circulation field dominated by southward currents.Current measurements from two mooring sites(C1: 8.67°N,95.68°E;C5:8.63°N,96.97°E)in 2017 were analyzed,the results showed that: a rapid transition of currents at both stations between May and June.Southward currents prevailed at site C1 during the second half of the year,while alternating north–south currents occurred at site C5,with northward currents dominating.Both zonal and meridional currents at the two moorings exhibited variations of 30–60 days,90 days,120 days and 180 days,which are found to be related to the effects of the equatorial Kelvin waves and basin resonances,with the signals more pronounced in the upper 100 m layer.