Interanual Salinity Variations Over Equatorial Indian Ocean In Relation To Indian Monsoon

As an important part of the global tropical ocean,the tropical Indian Ocean plays an important role in global climate evolution,especially in the Asian monsoon system.As an important source of East Asian monsoon water vapor,the Indian Ocean can affect the monsoon characteristics of East Asia.Precipitation affects local droughts and floods.Ocean salinity is a natural freshwater tracer in the global water cycle,and one of the most important physical parameters for regulating ocean thermodynamic processes.It can reflect the ocean's response to atmospheric anomalies and is also the global water cycle.And the key elements of climate anomalies,and their changes represent large-scale ocean-atmosphere coupled climate signals.The study of the equatorial Indian Ocean salinity change and its interaction with the monsoon is of great significance to the study of the climate in East Asia.This paper mainly uses Argo's monthly average salinity data,ERA-5's wind field,evaporative precipitation data,and SODA flow field data,and analyzes the equatorial Indian Ocean salinity and salinity through analysis methods such as EOF analysis,synthetic analysis,and correlation analysis.Its abnormal distribution and change characteristics,the main conclusions are as follows:(1)The salinity changes in the equatorial Indian Ocean are mainly in the upper ocean,especially the changes in the ocean surface,which have significant east-west distribution differences,seasonal and interannual changes.In the summer of El nino,the sea surface salinity of the equatorial Indian Ocean is large,showing a positive anomaly,while in winter,the salinity of the east of the equator is small,showing a negative anomaly;while in La nina,the salinity is negative in summer and the area is positive and abnormal in the east in winter.During the summer monsoon and winter monsoon periods in PIOD years,the equatorial Indian Ocean sea surface salinity presents a large negative anomaly,while it is opposite in NIOD years.(2)The onset of the El nino summer storm was delayed,and the wind field intensity and duration decreased,resulting in a decrease in the transport of low saline water from the southeast to the west,resulting in a larger equatorial Indian Ocean salinity and positive salinity;the winter wind field intensity in La nina Increased,resulting in increased transport of high salt water from the northwest to the east,thus presenting a positive anomaly in the east.In PIOD years,the summer monsoon increased and the winter monsoon weakened,resulting in an increase in low salt water input and a decrease in high salt water input,resulting in a large negative anomaly in sea surface salinity,which was the opposite in NIOD years.(3)During the Lanina summer monsoon,there was a westwardly enhanced flow field in the south-central equator,which resulted in a westward shift of the salinity contours in the southerncentral equator during the Lanina summer monsoon,resulting in negative salinity anomalies;while in the Lanina winter monsoon during the period,the eastward currents in the south of the equator increased,leading to positive salinity anomalies in the southeast region in winter,while the westward currents in the north increased,resulting in negative salinity anomalies in the west,which was roughly the opposite in El nino years.During the NIOD summer monsoon,the eastward flow field in the northern part of the central equator was relatively large,and the southeastward flow field was in the south,leading to the eastward transport of high salinity,which resulted in the positive anomaly of sea surface salinity in the entire equatorial Indian Ocean;while in PIOD years,there was a westward current in the southeastern part of the year,and a weaker eastward current in the north,resulting in a decrease in overall salinity,resulting in negative salinity anomalies.During the winter monsoon period,the westward current in the north increased in PIOD years,resulting in a positive anomaly in the northwest,a weakening of the westward current in the south,and a positive anomaly in the southeast.In NIOD years,the opposite was true.Compared with ENSO events,IOD events have a more significant effect on the anomalous changes of equatorial Indian Ocean currents and sea surface salinity,and there is a certain lag.The lag time of ENSO in the central equatorial Indian Ocean,which has a significant impact,is 14 months.The coefficient is 0.314,the lag time of IOD is 5 months,and the correlation coefficient is-0.308.