Characteristics And Mechanism Of Sea Level Variations In The Red Sea

Oceans are the core components of the global climate system,and the variations will inevitably affect the rest of the climate system,natural environment and ecosystem,thus affecting people's living environment.The Red Sea is located between the northeastern Africa and the Arabian Peninsula,which is the main thoroughfare connecting the Indian Ocean and the Mediterranean Sea.The Red Sea is also one of the core nodes of the ‘21st-Century Maritime Silk Road',which is a part of ‘One Belt One Road' aimed at peaceful development and common prosperity of China.The study of sea level variations and mechanism in the Red Sea is of great significance to disaster early warning,prediction and climate change research in the region,and can also provide reference for manual decision-making.In this paper,satellite altimetry,GRACE and temperature and salinity data are used to monitor the variations of the total sea level,mass-induced sea level and steric sea level of the Red Sea from 2003 to 2014.Due to the poor coverage and imperfection for single temperature-salinity dataset,we averaged three datasets(CORA,SODA,and ORAS4)to improve the spatial distribution and accuracy of the steric sea level variations.Leakage errors induced by truncation and spatial smoothing during GRACE postprocessing have great influence on small area.We propose an improved scale factor to correct the leakage error,which is validated by using satellite altimeter measurements.Annual amplitudes of mass-induced sea level variations in the Red Sea observed by JPL data for improved scaling factors is 20.4±2.2 cm,which is consistent with that inferred from satellite altimetry and temperature-salinity data(20.2±1.0 cm),and larger than that for traditional scaling factors(16.2±1.6 cm),indicating that the improved scale factor can effectively improve the accuracy of GRACE measurements.Due to the inaccuracy of the GLDAS data,which resulting in insufficient internal leakage correction,the long-term trend of JPL(-2.6±3.4 mm/yr)is significantly smaller than the altimeter-steric(4.6±2.0 mm/yr).Annual amplitude(16.4±2.2 cm)of the total sea level variations estimated by the combined GRACE and temperature-salinity data is comparable to satellite altimeter results(16.2±0.9 cm),indicating that the satellite altimetry,satellite gravity and temperature-salinity data have good consistency,which can constitute a closed-loop verification of monitoring the sea level variations in the Red Sea.Various data(wind stress,buoyancy flux,seawater velocity and so on)are used to analyze the influencing factors of steric sea level variations and mass-induced sea level variations in the Red Sea.The results show that heat flux is one of the main factors affecting the seasonal signals of steric sea level variations in the Red Sea,but lagged response existed between steric sea level variations and heat flux,while the freshwater flux is negligible.Annual amplitude(2.3±0.2 cm)of the steric sea level variations combining the Ekman pumping and buoyancy flux sea level variations in the mixed layer is consistent with that from temperature-salinity data(2.5±0.1 cm),implying that Ekman pumping and buoyancy flux dominate the steric sea level variations in the mixed layer of the Red Sea.Annual amplitude(2.5±0.4 cm)of the steric sea level variations under the mixed layer is consistent with that in the mixed layer,and the interannual signals of the steric sea level variations mainly from the 60~200 m depth.Compared with precipitation-evaporation,mass exchange between the Gulf of Aden and the Babel-Mandeb strait has a more significant effect on the mass variations in the Red Sea.Its correlation coefficient with the mass variations inferred from JPL data is 0.8,and dominates the seasonal signals of mass variations in the Red Sea.