| Solar irradiance is the most important energy source for the Earth.It determines weather and climate in the Earth system,affects the temperature of the atmosphere and sea water,and drives photosynthesis on land and in the ocean.Visible solar radiation(VSR,400-700 nm)can penetrate tens of meters into the ocean,so it could regulate the upper-ocean temperature,mixing patterns and the photosynthesis of phytoplankton in the mixed layer and deeper layer of the ocean.Therefore,accurate estimate of the vertical distribution of VSR in the upper-water column is important for several aspects of oceanography research.In the past decades,ocean modelling has become an important tool for oceanography research.In order to improve the accuracy of the ocean model results,it is necessary to calculate the transmission of VSR correctly in the models.Wrong VSR distribution could lead to errors in the simulation results of ocean temperature,heat flux,mixing and phytoplankton growth.Researchers have developed a variety of VSR transmission schemes,but the most widely used in the ocean model is still a relatively simple and rough model.In addition,many studies have tried to modify VSR transmission schemes in ocean models to study the effects of radiation uptake by phytoplankton,but the results of these studies are inconsistent.In this study,we discussed the existing VSR transmission schemes and the photosynthetically active radiation(PAR)transmission schemes,and chose the most accurate schemes which were based on the inherent optical properties(IOP)of seawater.Then we incorporated them into the ocean dynamical model and ocean biological model by modifying the code of the model,analyzed the differences of the simulation results before and after the modification,and discussed the importance of accurate VSR transmission schemes for ocean models.(1)Experiment on the impact of VSR transmission schemes in onedimensional ocean physical modelIn order to investigate the effect of direct heating process of solar radiation on temperature and mixing in the upper ocean,we incorporated different transmission schemes into a one-dimensional ideal ocean physical model.Although all model runs used the same ocean color information and the same circulation model,the IOP-and Chl-based schemes resulted in very different vertical temperature and upper-water mixing from the default scheme,with a maximum difference in temperature up to 2℃,and a maximum difference in mixed layer depth(MLD)up to～30 m.The effect of transmission scheme is more obvious for clear waters(Chl<0.3mg m-3).These results suggested that,without considering the horizontal transport of the sea water,the different transmission schemes would cause significant differences in the thermodynamical processes in the upper ocean.Therefore,a proper transmission scheme is critical for broad basin-scale circulation modeling.(2)Experiment on the impact of VSR transmission schemes in threedimensional ocean physical model in the South China SeaSolar radiation impacts sea water temperature in ocean physical models not only by direct heating processes,but also by affecting dynamic processes,which could in turn lead to more significant changes in ocean temperature.Based on the method and results of first part,we conducted the experiment on the impact of modifying VSR transmission scheme in the three-dimensional ROMS dynamical model in the South China Sea.Differences between the ocean model results using the default scheme based on water type and the scheme based on IOP were compared.The results showed that,in some regions,the influence of the VSR transmission schemes on the model temperature was amplified by ocean dynamic processes.In summer,the maximum difference of sea surface temperature is about 0.5℃,while the maximum difference is about 3℃ at 20 m and 4℃ at 100 m.In addition to comparing the temperature distribution at different depths,we also investigate the influence of VSR transmission schemes on the seasonal variation of temperature in different regions and depths by correlation analysis with monthly climatology temperature data from Simple Ocean Data Assimilation Reanalysis(SODA).It was found that,compared with the default,spatiotemporal-invariant VSR transmission scheme,the correlation of monthly averaged temperature between model results using IOP-based scheme with SODA was improved obviously.Besides,we also discussed the impact of the modifying VSR transmission scheme in ocean model on ocean dynamic process,the Kuroshio intrusion(KI)at Luzon Strait.The results showed that the intensity and intrusion path of KI resulted from IOP-based scheme were significantly different from the default transmission scheme.The Luzon Strait transport increased by 50%,and the probability of different paths of Kuroshio invasion changed obviously.The most significant change was the appearance of anticyclonic loop at southwest of Taiwan in the winter after the modification of the VSR transmission scheme.(3)Experiment on the impact of VSR transmission scheme for both dynamic and biology in a fully coupled physical-biological ocean modelSolar radiation not only plays an important role in ocean thermodynamic process,but also determinates the processes in marine ecosystem.However,it is common that two different VSR transmission schemes employed separately in the physics(dynamics)and biology sides even in coupled models,thus for the same depth different VSR values are used for the two sides.Consequently,the interactions or feedbacks between physics and biology obtained from such a coupled model are skeptical.Therefore,we used an ideal one-dimensional coupled ocean dynamicbiological model is established in the center South Pacific Gyre,and incorporated an IOP-based VSR transmission scheme in both physical and biological model.The results showed that the fully coupled model with a unified VSR transmission scheme resulted in significantly different vertical profiles of temperature and Chl compared to that using the default scheme in ROMS.Therefore,in the oligotrophic ocean,the differences of model results in temperature can be up to 1.5-2℃,with difference in subsurface chlorophyll maximums layer(SCMs)depth in summer up to～75 m and difference in the MLD in winter up to-45 m.These results highlight not only the importance of the feedback from biological process to dynamics,but also the necessity of using unified and accurate VSR transmission scheme in fully coupled physical-biological ocean models.To sum up,in this study,the impact of the improving of the solar radiation transmission scheme was investigated in the one-dimensional ideal physical model,the three-dimensional physical model in the South China Sea and the one-dimensional ideal physical-biological coupled model.Although there were limitations due to the use of climatology data as forcing conditions and the lack of adjustment of biological model parameters,the present results have shown that,it is necessary to use accurate VSR transmission scheme in the ocean models.In the ocean physical model,incorporating IOP data from satellite remote sensing could effectively improve the simulation of the temperature vertical distribution,and in physical-biological coupled model,fully coupled VSR transmission model could significantly influence the vertical distribution of both Chl and temperature in model result.These results are helpful for researchers to understand of the importance of solar radiation in ocean models and of great positive significance for the improving ocean models in the future. |
