A filter method that combines ensemble empirical modal decomposition(EEMD)and wavelet analysis methods was proposed to separate and correct the global navigation satellite system(GNSS)multipath error more effectively....A filter method that combines ensemble empirical modal decomposition(EEMD)and wavelet analysis methods was proposed to separate and correct the global navigation satellite system(GNSS)multipath error more effectively.In this method,the GNSS signal is first decomposed into several intrinsic mode functions(IMFs)and a residual through EEMD.Then,the IMFs and residual are classified into noise terms,mixed terms,and useful terms according to a combined classification criterion.Finally,the mixed term denoised by wavelet and the useful term are reconstructed to obtain the multipath error and thus enable an error correction model to be built.The measurement data provided by the Curtin GNSS Research Center were used for processing and analysis.Results show that the proposed method can separate multipath error from GNSS data to a great extent,thereby effectively addressing the defects of EEMD and wavelet methods on multipath error weakening.The error correction model established with the separated multipath error has a higher accuracy and provides a certain reference value for research on related signal processing.展开更多
The response of atmospheric circulation to sea surface temperature anomaly(SSTA)of different scales in extratropical oceans has always been a popular issue in air-sea interactions,especially regarding the influence of...The response of atmospheric circulation to sea surface temperature anomaly(SSTA)of different scales in extratropical oceans has always been a popular issue in air-sea interactions,especially regarding the influence of widely active,small-scale ocean eddies on the atmosphere.Based on the regional climate model RegCM4.6,three sets of ensemble experiments with different initial values were designed,and the response of atmospheric circulation and possible mechanisms to Kuroshio Extension Decadal Variability SSTA with different scales(KEDV-induced SSTA)during winter were discussed.The response of atmospheric circulation to the KEDV-induced mesoscale SSTA presents a broadly tripolar pattern,while the response to the KEDV-induced large-scale SSTA presents a baroclinic structure in the central Pacific and a dipole-type response with a barotropic structure in the eastern Pacific.Further diagnostic analysis shows that under the influence of mesoscale SSTA,transient eddy activity is strengthened,and feedback of transient eddy plays a major role in the large-scale circulation anomaly in the central-eastern Pacific.The associated barotropic energy conversion also plays an important role in maintaining the largescale circulation anomaly in the northwestern Pacific Ocean.Under the influence of large-scale SSTA,diabatic heating is stronger,and the feedback of diabatic heating plays a major role in the large-scale circulation anomaly.展开更多
Alpine grassland is the main ecosystem of the Tibetan Plateau(TP),thus accurate simulation of water and heat exchange in the grassland will significantly enhance the understanding of the land-atmosphere interaction pr...Alpine grassland is the main ecosystem of the Tibetan Plateau(TP),thus accurate simulation of water and heat exchange in the grassland will significantly enhance the understanding of the land-atmosphere interaction process on the TP.In this study,we assessed and improved the ensemble numerical simulations of the community Noah land surface model with multiparameterization options(Noah-MP)by using observations collected from four alpine grassland observation sites.The four observation sites belong to the upper Heihe River Basin Integrated Observatory Network located in the northeastern part of the TP.First,an ensemble of 1008 numerical simulation experiments,based on multiparameterization options of seven physical processes/variables in the Noah-MP,was carried out for the vegetation growing season.The Taylor skill score was then used to assess the model performance and select the optimal combination of parameterization options for a more exact simulation of the water and heat exchange in alpine grassland.The accuracy of Noah-MP simulation was further improved by introducing new parameterizations of thermal roughness length,soil hydraulic properties,and vertical root distribution.It was found that:(1)Simulation of water and heat exchange over alpine grassland in the growing season was mainly affected by the parameterizations of dynamic vegetation,canopy stomatal resistance,runoff and groundwater dynamics,and surface exchange coefficient for heat transfer.Selection of different parameterization options for these four physical processes/variables led to large differences in the simulation of water and heat fluxes.(2)The optimal combination of parameterization options selected in the current Noah-MP framework suffered from significant overestimation of sensible heat flux(H)and underestimation of soil moisture(θ)at all observation sites.(3)The overestimation of H was significantly improved by introducing a new parameterization of thermal roughness length.Furthermore,the underestimation ofθwas resolved by introducing a new parameterization of soil hydraulic properties that considered the organic matter effect and a new vertical distribution function for the vegetation root system.The results of this study provide an important reference for further improving the simulation of water and heat exchange by using the land surface model in alpine grassland.展开更多
基金The National Natural Science Foundation of China(No.41974030)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX17_0150).
文摘A filter method that combines ensemble empirical modal decomposition(EEMD)and wavelet analysis methods was proposed to separate and correct the global navigation satellite system(GNSS)multipath error more effectively.In this method,the GNSS signal is first decomposed into several intrinsic mode functions(IMFs)and a residual through EEMD.Then,the IMFs and residual are classified into noise terms,mixed terms,and useful terms according to a combined classification criterion.Finally,the mixed term denoised by wavelet and the useful term are reconstructed to obtain the multipath error and thus enable an error correction model to be built.The measurement data provided by the Curtin GNSS Research Center were used for processing and analysis.Results show that the proposed method can separate multipath error from GNSS data to a great extent,thereby effectively addressing the defects of EEMD and wavelet methods on multipath error weakening.The error correction model established with the separated multipath error has a higher accuracy and provides a certain reference value for research on related signal processing.
基金This work was supported by the National Nature Science Foundation of China(Grant No.41490642).
文摘The response of atmospheric circulation to sea surface temperature anomaly(SSTA)of different scales in extratropical oceans has always been a popular issue in air-sea interactions,especially regarding the influence of widely active,small-scale ocean eddies on the atmosphere.Based on the regional climate model RegCM4.6,three sets of ensemble experiments with different initial values were designed,and the response of atmospheric circulation and possible mechanisms to Kuroshio Extension Decadal Variability SSTA with different scales(KEDV-induced SSTA)during winter were discussed.The response of atmospheric circulation to the KEDV-induced mesoscale SSTA presents a broadly tripolar pattern,while the response to the KEDV-induced large-scale SSTA presents a baroclinic structure in the central Pacific and a dipole-type response with a barotropic structure in the eastern Pacific.Further diagnostic analysis shows that under the influence of mesoscale SSTA,transient eddy activity is strengthened,and feedback of transient eddy plays a major role in the large-scale circulation anomaly in the central-eastern Pacific.The associated barotropic energy conversion also plays an important role in maintaining the largescale circulation anomaly in the northwestern Pacific Ocean.Under the influence of large-scale SSTA,diabatic heating is stronger,and the feedback of diabatic heating plays a major role in the large-scale circulation anomaly.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDA20100101,XDA20100103)。
文摘Alpine grassland is the main ecosystem of the Tibetan Plateau(TP),thus accurate simulation of water and heat exchange in the grassland will significantly enhance the understanding of the land-atmosphere interaction process on the TP.In this study,we assessed and improved the ensemble numerical simulations of the community Noah land surface model with multiparameterization options(Noah-MP)by using observations collected from four alpine grassland observation sites.The four observation sites belong to the upper Heihe River Basin Integrated Observatory Network located in the northeastern part of the TP.First,an ensemble of 1008 numerical simulation experiments,based on multiparameterization options of seven physical processes/variables in the Noah-MP,was carried out for the vegetation growing season.The Taylor skill score was then used to assess the model performance and select the optimal combination of parameterization options for a more exact simulation of the water and heat exchange in alpine grassland.The accuracy of Noah-MP simulation was further improved by introducing new parameterizations of thermal roughness length,soil hydraulic properties,and vertical root distribution.It was found that:(1)Simulation of water and heat exchange over alpine grassland in the growing season was mainly affected by the parameterizations of dynamic vegetation,canopy stomatal resistance,runoff and groundwater dynamics,and surface exchange coefficient for heat transfer.Selection of different parameterization options for these four physical processes/variables led to large differences in the simulation of water and heat fluxes.(2)The optimal combination of parameterization options selected in the current Noah-MP framework suffered from significant overestimation of sensible heat flux(H)and underestimation of soil moisture(θ)at all observation sites.(3)The overestimation of H was significantly improved by introducing a new parameterization of thermal roughness length.Furthermore,the underestimation ofθwas resolved by introducing a new parameterization of soil hydraulic properties that considered the organic matter effect and a new vertical distribution function for the vegetation root system.The results of this study provide an important reference for further improving the simulation of water and heat exchange by using the land surface model in alpine grassland.
