Development And Demonstration Application Of Global Ocean Surface Current Products Based On Satellite Altimetry And Temperature Measurement

Ocean Surface Current(OSC)usually refers to the relatively stable seawater flow at a depth of 15 m below the sea surface.The movement of surface water bodies and the transport of materials and energy play an important role in climate change,pollution diffusion,fisheries and ship navigation.The current mainstream surface current remote sensing products have low accuracy and do not utilize high-resolution Sea Surface Temperature(SST)information that can provide global coverage daily,while high-resolution SST can include sub-mesoscale processes that can provide information on smaller spatial scales.In order to further improve the accuracy of surface current products and obtain rich sub-mesoscale information,this paper takes the mainstream foreign Glob Current surface current products based on satellite altimetry as background currents,introduces high-resolution Sea Surface Temperature information,studies the generation method of surface current products,analyzes the sensitivity of surface current products to SST data,generates the global ocean surface current gridding products with long time series from 1999 to 2018,and evaluates the product quality by using the measured data of drifting buoys.Finally,the demonstration application of surface current products is carried out.The research contents of this paper include:(1)research on the generation method of surface current products based on satellite altimetry and satellite temperature measurement data,giving the calculation method of surface current in two cases of known forcing and unknown forcing;(2)Based on SST data with three different spatial resolutions,the sensitivity of surface current products to SST is analyzed;(3)Based on Glob Current surface current products and MW SST data,using the unknown forcing surface current calculation method,the daily global ocean surface current gridding products from 1999 to 2018 are generated,and the quality of surface current products is evaluated by using the in-situ observation data of drifting buoys;(4)The demonstration application of surface current products was carried out in the Kuroshio region of the northwest Pacific Ocean and Leeuwin Current(LC)region of the southeast Indian Ocean and the west coast of Australia to analyze the characteristics of flow field and Eddy Kinetic Energy changes.The main conclusions of this paper are as follows:(1)The surface current calculation method with known forcing may produce anomalous velocities in the region of weak Sea Surface Temperature Gradient(SSTG),while the surface current calculation method with unknown forcing successfully solves this problem by obtaining significant improvements in the normal velocity component along the isotherm while keeping the tangential velocity component along the isotherm constant.(2)The accuracy of surface current products strongly depends on the quality of SST data,and decreases with the increase of SST analysis error.In the high latitude region,the zonal components of the surface current based on MW SST,MWIR SST and OSTIA SST have been negatively improved in different degrees.MW SST has a deterioration of about-5%,and MWIR SST is worse,and the deterioration of OSTIA SST is significantly reduced compared with MWIR SST.On the whole,the improvement percentage of surface current based on different SST has similar regional differences,and the average improvement level of MW SST is the highest,while OSTIA SST is the worst.In local areas,high-resolution SST can add small-scale information to the background current,which highlights the local application potential of high-resolution SST data.(3)The unknown forcing surface current calculation method can effectively improve the Ocean Surface Current,which means that the method can be used to generate long-term series of gridded surface current products,in which the Sea Surface Temperature information plays a great role in correcting the background current.SST observations can provide information on a smaller spatial scale to compensate the lack of altimetry data.Surface current products can make full use of the advantages of high-resolution SST data,and the meridional component and zonal component can be improved by 0.7%?16.5% and 0.5%?6%,respectively,and they have been improved at a higher level in equatorial zone and western boundary current region.Surface current in areas with strong mesoscale activities and strong temperature gradients tend to perform better,which indicates that surface current products generated by introducing SST information can effectively improve background current based on satellite altimetry in areas with strong Sea Surface Temperature Gradient(SSTG).(4)The flow path and velocity variation of Kuroshio and LC can be obtained based on the average current field of surface current products.The Eddy Kinetic Energy(EKE)of the Kuroshio Extension(KE)has obvious low-frequency oscillation on the interdecadal time scale,which is mainly manifested as the oscillation between the “elongated state” of narrow strong stable jet and the “contracted state” of broad unstable jet.In order to better monitor these two states,a Kuroshio Index(KI)based on the average Eddy Kinetic Energy of Kuroshio Extension sub-region(32°N-37°N,141°E-149°E)is defined to characterize the long-term variation characteristics of KE region.According to KI time series,the elongation state periods of Kuroshio Extension are 2002-2004,2011,2015 and 2018,and the contraction state periods are1999-2001 and 2009.By calculating the multi-year seasonal average Eddy Kinetic Energy in Kuroshio region,it is found that the Eddy Kinetic Energy in this region also has the seasonal variation characteristics of strong summer and weak winter.The power spectrum analysis of average Eddy Kinetic Energy in different Kuroshio flow sections shows that EKE in each Kuroshio flow section has quasi-decadal interdecadal oscillation characteristics.The analysis results of the LC region show that the Eddy Kinetic Energy level of LC and South Indian Countercurrent(SICC)region is relatively high,and the Eddy Kinetic Energy of LC region has seasonal variation characteristics of weak summer and strong winter,and the Eddy Kinetic Energy of SICC region lags behind LC obviously.In addition,the most significant change periods of LC and SICC regions are 1 a and 10 a.The demonstration application of the surface current products in the Kuroshio and LC regions shows that the product provides a good estimation of global ocean surface current,and can be used for the analysis and research of the global ocean upper circulation.