In Earth system modeling,the land surface is coupled with the atmosphere through surface turbulent fluxes.These fluxes are computed using mean meteorological variables between the surface and a reference height in the...In Earth system modeling,the land surface is coupled with the atmosphere through surface turbulent fluxes.These fluxes are computed using mean meteorological variables between the surface and a reference height in the atmosphere.However,the dependence of flux computation on the reference height,which is usually set as the lowest level in the atmosphere in Earth system models,has not received much attention.Based on high-resolution large-eddy simulation(LES)data under unstable conditions,we find the setting of reference height is not trivial within the framework of current surface layer theory.With a reasonable prescription of aerodynamic roughness length(following the setting in LESs),reference heights near the top of the surface layer tend to provide the best estimate of surface fluxes,especially for the momentum flux.Furthermore,this conclusion for the sensible heat flux is insensitive to the ratio of roughness length for momentum versus heat.These results are robust,whether using the classical or revised surface layer theory.They provide a potential guide for setting the proper reference heights for Earth system modeling and can be further tested in the near future using observational data from land–atmosphere feedback observatories.展开更多
To achieve the goal that China and Nepal jointly announce the new height of Mount Qomolangma(MQ),the campaign of Qomolangma Height Survey(QHS)was carried out from 2019 to 2020.A high precision geoid model realizing th...To achieve the goal that China and Nepal jointly announce the new height of Mount Qomolangma(MQ),the campaign of Qomolangma Height Survey(QHS)was carried out from 2019 to 2020.A high precision geoid model realizing the common height datum for both sides is necessary for determining the unique height of MQ.However,high altitude and rugged topography make it extremely difficult to conduct terrestrial gravity measurements in this region,the accuracy of geoid model is restricted by terrestrial gravity data gaps.In the campaign of 2020 QHS,the airborne gravity survey was carried out over MQ and its surrounding areas,the airborne gravity data covering an area of 12,700 km^(2) were successfully collected.For the first time,the high precision observations of terrestrial gravity and BeiDou Navigation Satellite System(BDS)at the peak of MQ were collected.These datasets pave the way for the precise determination of the orthometric height of MQ.According to the definition of the International Height Reference System(IHRS),we developed the IHRS-based gravimetric quasigeoid model by combining the airborne and terrestrial gravity data.Validations against highly accurate GNSS leveling data at 61 benchmarks demonstrate that the accuracy of the quasigeoid model is 3.8 cm,and the addition of airborne gravity data improves the accuracy by 51.3%.Based on the IHRS,the final orthometric height of the snow surface of the peak of MQ is determined to be 8848.86 m.展开更多
The contribution presents the representative research progress on global static gravity field modeling,regional geoid/quasigeoid determination,vertical datum study,as well as the theory,algorithm and software for grav...The contribution presents the representative research progress on global static gravity field modeling,regional geoid/quasigeoid determination,vertical datum study,as well as the theory,algorithm and software for gravity field study in China from 2019 to 2023,which are the highlights of the chapter 6“Progress in Earth Gravity Model and Vertical Datum”in the“2019—2023 China National Report on Geodesy”that submitted to the International Association of Geodesy(IAG).In addition,suggestions are proposed to promote the research in the fields of earth gravity field,geoid/quasigeoid and vertical datumin China according to trends of international geodesy and related disciplines.展开更多
基金supported by the Natural Science Foundation of China(Grant Nos.42088101 and 42375163)the Guangdong Major Project of Basic and Applied Basic Research(Grant No.2021B0301030007)the specific research fund of The Innovation Platform for Academicians of Hainan Province(Grant No.YSPTZX202143)。
文摘In Earth system modeling,the land surface is coupled with the atmosphere through surface turbulent fluxes.These fluxes are computed using mean meteorological variables between the surface and a reference height in the atmosphere.However,the dependence of flux computation on the reference height,which is usually set as the lowest level in the atmosphere in Earth system models,has not received much attention.Based on high-resolution large-eddy simulation(LES)data under unstable conditions,we find the setting of reference height is not trivial within the framework of current surface layer theory.With a reasonable prescription of aerodynamic roughness length(following the setting in LESs),reference heights near the top of the surface layer tend to provide the best estimate of surface fluxes,especially for the momentum flux.Furthermore,this conclusion for the sensible heat flux is insensitive to the ratio of roughness length for momentum versus heat.These results are robust,whether using the classical or revised surface layer theory.They provide a potential guide for setting the proper reference heights for Earth system modeling and can be further tested in the near future using observational data from land–atmosphere feedback observatories.
基金supported by the National Natural Science Foundation of China[grant numbers 41974010,42074020]the basic scientific research operating program of Chinese Academy of Surveying and Mapping。
文摘To achieve the goal that China and Nepal jointly announce the new height of Mount Qomolangma(MQ),the campaign of Qomolangma Height Survey(QHS)was carried out from 2019 to 2020.A high precision geoid model realizing the common height datum for both sides is necessary for determining the unique height of MQ.However,high altitude and rugged topography make it extremely difficult to conduct terrestrial gravity measurements in this region,the accuracy of geoid model is restricted by terrestrial gravity data gaps.In the campaign of 2020 QHS,the airborne gravity survey was carried out over MQ and its surrounding areas,the airborne gravity data covering an area of 12,700 km^(2) were successfully collected.For the first time,the high precision observations of terrestrial gravity and BeiDou Navigation Satellite System(BDS)at the peak of MQ were collected.These datasets pave the way for the precise determination of the orthometric height of MQ.According to the definition of the International Height Reference System(IHRS),we developed the IHRS-based gravimetric quasigeoid model by combining the airborne and terrestrial gravity data.Validations against highly accurate GNSS leveling data at 61 benchmarks demonstrate that the accuracy of the quasigeoid model is 3.8 cm,and the addition of airborne gravity data improves the accuracy by 51.3%.Based on the IHRS,the final orthometric height of the snow surface of the peak of MQ is determined to be 8848.86 m.
基金National Key R&D Program of China(Nos.2021YFB3900200,2021YFB3900203)。
文摘The contribution presents the representative research progress on global static gravity field modeling,regional geoid/quasigeoid determination,vertical datum study,as well as the theory,algorithm and software for gravity field study in China from 2019 to 2023,which are the highlights of the chapter 6“Progress in Earth Gravity Model and Vertical Datum”in the“2019—2023 China National Report on Geodesy”that submitted to the International Association of Geodesy(IAG).In addition,suggestions are proposed to promote the research in the fields of earth gravity field,geoid/quasigeoid and vertical datumin China according to trends of international geodesy and related disciplines.
