| Solar radiation is the core of the earth’s energy source and a key factor affecting the thermal dynamics of the atmosphere,ocean and the air-sea interaction.Shortwave solar radiation can penetrate into the upper water body of the ocean,heating the water and changing its temperature,thus affecting other physical properties of the ocean.When the thermal structure of upper ocean water changes,fluid mixing,convection,heat exchange and other processes are affected,resulting in changes in physical properties such as density,mixed layer depth(MLD),current field,heat flux,ocean heat content(OHC)and so on.The Northwest Atlantic(NWA)has a complex marine topography and circulation dynamic system.The famous Gulf Stream transports a large amount of marine material and heat.It is the most significant feature of NWA sea water movement and one of the important western boundary currents in the world.At the same time,the complex optical characteristics of water bodies in the sea area are not the same,making it an ideal experimental area for studying optical-physical coupling models,which is very suitable for studying the effects of penetration mode of solar short-wave radiation in water bodies on simulating the ocean thermal dynamic characteristics and air-sea interaction.The main focus of this dissertation is to accurately describe the importance of solar shortwave radiation transmission in the NWA to the simulation of thermal dynamic characteristics and air-sea interaction in the upper ocean.In the early stage,the double exponential radiative transfer scheme based on Jerlov water body type was easy to calculate and widely used in various circulation models or coupling models.Because the water type scheme is too rough,it is difficult to simulate the underwater light field accurately.In recent decades,with the rapid development of satellite remote sensing,it is more convenient for people to obtain ocean optical parameters.Therefore,the marine surface chlorophyll concentration and inherent ocean properties(IOPs)schemes based on satellite remote sensing have been proposed successively by researchers.However,its application in a large environment like NWA is still blank,so the impact of the shortwave radiation penetration mode in water on a wide range of ocean thermal simulation and air-sea interaction is still unknown.In order to break through the above problems,it is necessary to simulate the basic physical field and current field of NWA by coupling more accurate shortwave radiation transmission scheme with circulation model,calculate the ocean heat budget,heat content,MLD and other physical quantities,and study the potential relationship between underwater shortwave radiation penetration and hurricane.In this study,the Regional Ocean Modeling System(ROMS)was used to simulate the threedimensional ocean state during the 2017 Atlantic hurricane active season.The circulation model was coupled with different underwater solar shortwave radiation transmission schemes.Three groups of three-dimensional sensitivity experiments were conducted:(1)Control experiment(Lee05 experiment):The radiation transmission scheme of water body in the ROMS optical module adopts the scheme based on IOPs[1],and the input optical parameters are from the satellite MODIS climatology monthly mean data.(2)Sensitivity experiment 1(WTYPE1 experiment):The radiation transmission scheme of water body in ROMS optical module adopts the default PS 77 empirical model[2],and the water type is set as Jerlov type 1,which represents clear water.(3)Sensitivity experiment 2(WTYPE9 experiment):The radiation transmission scheme of water body in ROMS optical module still adopts the default PS77 empirical model,but the water type is set to 9,representing turbid water body.The results of the three groups of comparative experiments are mainly used to explore the effects of different short-wave radiation transmission schemes on the simulated upper ocean thermal dynamic structure,physical field properties,OHC and air-sea interaction.Compared with various in-situ data,Lee05 results are the most similar to real ocean characteristics,and the simulation performance is the best.Three sets of experimental results show that different shortwave radiation transmission schemes in ocean models may cause large temperature structure differences.The SST plane results show that the WTYPE9 experimental simulation is significantly higher in summer,indicating that the turbidity water absorbs more heat in the surface layer.In summer,most sea surface SST of NWA presents the characteristics of WTYPE9>Lee05>WTYPE1,and the maximum absolute temperature difference between Lee05 and PS77 can exceed 1℃.In winter,the SST of most of the NWA sea presents the characteristics of WTYPE1>Lee05>WTYPE9,which is contrary to the surface characteristics in summer.The SST difference is obvious,and the maximum absolute temperature difference between Lee05 and PS77 is over 1.5℃.Moreover,the three models simulate different circulation patterns and warm vortex patterns on the surface of the Gulf of Mexico.The differences in vertical temperature structures of the three models in summer are as follows:(1)In the open ocean,the maximum vertical temperature difference between Lee05 and PS77 across the ocean occurs in the subsurface,and the absolute temperature difference can be as high as 1℃.(2)In the coastal cross section,thermal stratification is present,and the subsurface temperature structure is different.Compared to WTYPE1,Lee05 has a warmer water layer at the top 10m and a cooler water layer at 10 m to 45 m.Lee05 and WTYPE9 have the opposite differential characteristics,with Lee05 producing a cooler(warmer)upper(lower)water column than WTYPE9.Compared with Lee05 experiment,a warmer surface and a cooler deep layer are formed in WTYPE9 experiment.In the comparison between the two groups,the absolute temperature of Lee05 and PS77 was significantly different,with values as high as 1℃.In addition to the temperature difference,the simulation results of density are different.Using different optical penetration schemes,the simulation results of current field velocity and flow direction in the physical ocean model show significant changes,and the changes are more significant in winter than in summer.The maximum experimental velocity difference between Lee05 and PS77 in the NWA was over 0.3 m·s-1 in summer and 1 m·s-1 in winter.The Gulf Stream region and its vortex diffusion region are particularly different.In Lee05 and PS77 experiments,the percentage difference of current velocity in the large area east of the Gulf Stream reached 100%in summer,and the range expanded to the large area in the central Gulf of Mexico and the southern Caribbean in winter.The heat transport in winter(0 to 50℃·ms-1)is less than that in summer(0 to 70℃ · ms-1),and the values are obviously higher in the Loop current and Gulf Stream.In summer and winter,Lee05 experiment and PS77 experiment showed positive and negative heat transport differences,presenting spatial staggered distribution.Compared with WTYPE1,Lee05 experiment showed that the heat transport difference ranged from ± 15℃·ms-1 in summer to±20℃·ms-1 in winter.Lee05 experiment compared with WTYPE9 experiment,the heat transport difference between the two is about ±10℃·ms-1 in summer and about ±20℃·ms-1 in winter.The variation difference of heat transport in winter was larger than that in summer.In summer,the percentage difference between Lee05 experiment and PS77 experiment reached 100%in many ocean areas outside the eastern boundary of the Gulf Stream,indicating that heat transport was completely variable in these areas.Compared with summer,the variation of heat transport in winter is deeper and wider.The control experiment using Lee05 scheme was significantly better than the two sensitivity experiments using PS 77 scheme,especially in ocean circulation simulations,where a difference of up to 30%in OHC was calculated using PS 77 scheme compared with Lee05 scheme.Based on a semi linear relationship between the intensity of the five major hurricanes OHC in 2017,the 30%OHC change was proportional to a change in sea level pressure(SLP)of about 20 mb,greater than the SLP difference between the continuous Saffir-Simpson hurricane category.The results of the model experiments in this dissertation are verified by OHC analysis based on field temperature observations and remote sensing inversion.It shows that different radiation transmission schemes in the physical ocean model can simulate different ocean thermal dynamic structures.The selection of radiative transmission scheme has a significant effect on the accuracy of upper thermal structure,circulation and OHC predicted by the model.Therefore,ocean optical properties and the application of accurate radiative transmission scheme in ocean model play an important role in hurricane intensity prediction.The results of this dissertation emphasize the importance of using an IOPs based radiative transmission scheme in ocean and storm forecasting. |
PDF Full Text Request