| The Arabian Sea(AS)has a unique geographical position,located in one of the regions with the highest sea surface temperature(SST)in the world,as an important part of the underlay of Indian monsoon region,being surrounded on three sides by the mainland and has significant monsoon climate,its thermal condition's changes affect the Indian monsoon,the east Asian monsoon and the global climate through the interaction of ocean and atmosphere.Temperature data in the AS ocean was relatively scarce in the early days,limited understanding of the AS ocean temperature.The appearance of Array for Real-time Geostrophic Oceanography provides high spatial and temporal resolution ocean temperature data for the study oin the AS.Argo gridded data set(temperature),simple ocean data assimilation monthly ocean data set(flow field)and cross calibrated multi-platform wind field data were used to reveal the double-peak variation feature of the twice warming and twice cooling processes at 5m,50 m,100m and 200 m of ocean temperature in the AS via empirical orthogonal functions(EOF).Based on the EOF results,the reasons for the double-peak variation feature of the upper sea temperature in AS are obtained through quantitative discussion(we qualitatively discussed the reasons for the double-peak variation feature of the upper sea temperature in AS).Afterwards,the contributions from the surface heat forcing,vertical entrainment,Ekman advection,and geostrophic advection to the seasonal variation of the upper sea temperature is quantitatively estimated by using ocean heat balance equations of mixed-layer in AS,through which we discuss the influence of the external ocean(atmosphere)on the ocean temperature in AS.Finally,we choose a 8.75°N section in AS,and analyse the effect of heat transport between the8.75°N section in AS and the equatorial western Indian ocean on seasonal variation of ocean temperature in AS.Reveal the double-peak variation feature of the twice warming and twice cooling processes at 5m,50 m,100m and 200 m of ocean temperature of the AS by EOF,the results indicate that the double-peak pattern of 5m is found in the first mode which explained 75.79% variance contribution rate over the domain.The temperature variationof 5m is mainly influenced by wind,solar radiation and wind-driven circulation.The double-peak pattern of 50 m is found in the third mode which explained 11.95%variance contribution rate over the domain.In this layer temperature variation is mainly influenced by wind-driven circulation.The double-peak pattern of 100 m is found in the first and the third mode which explained 52.03% and 9.55% variance contribution rate,respectively.The first mode of 100 m shows that the temperature in 100 m ranges with maximum amplitude,and 100 m of the AS is amongst the thermocline of which temperature changes most dramatically in the ocean,therefore the temperature in 100 m ranges with maximum amplitude and extension.The distribution of ocean temperature at 100 m is mainly governed by wind stress curl and thermocline.When the wind stress curl is downward,atmospheric forcing the ocean leads to the convergence of the local sea water,and thus thermocline deepened induces the increase of ocean temperature at100 m in some regions;in contrast when the wind stress curl is upward,atmospheric pumping the ocean leads to the divergence of the local sea water,and thus deep cold water rise results the decrease in temperature at 100 m in some regions.The results of quantitative estimation of the heat balance equation of ocean mixing layer show that both the seasonal variation of net heat flux in AS and the seasonal variation of ocean temperature at 5m layers have seasonal characteristics of twice warming and twice cooling in one year.The overall cooling of the mixed layer in the AS during the first cooling phase(from Oct.to Jan.of the following year)was mainly caused by the decrease greatly surface thermal forcing(relative contribution is 5.36%),in addition,the southern AS were cooled by geostrophic advection(relative contribution is 50.47%),which resulted in the largest cooling of the AS in the winter finally;the overall cooling of the mixed layer in the AS during the second cooling phase(from May to Jul.)was mainly caused by the Ekman cold advection(relative contribution is59.38%),the secondary role are sea surface thermal force(relative contribution is29.67%,20% less than the previous stage),geostrophic cold advection(relative contribution is 8.44%)and vertical entrainment(relative contribution is 2.51%).AS gains 7.75×1012W heat quantity whole year through the ocean-atmosphere heatexchange,but loses 8.6×1012W heat quantity whole year through the 8.75°N section,both of them are basically equal,indicating that the heat transport volume from the ocean-atmosphere heat exchange in AS is mainly towards the equatorial western Indian ocean,the heat exchange between the AS and the equatorial western Indian ocean plays a very important role in maintaining the basic balance of the ocean temperature in the AS.The result of the advance lag correlation analysis between the heat transport volume and ocean temperature in each layer shows that the impact of hear transport volume on double-peak feature of the temperature in 10 m layer is significant,but on double-peak feature of the temperature in 50 m,100m,200 m layer is less affected. |
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