A global forecast model is used to examine various sensitivities of numerical predictions of three extreme winter storms that occurred near the eastern continental margin of North America: the Ohio Valley blizzard of ...A global forecast model is used to examine various sensitivities of numerical predictions of three extreme winter storms that occurred near the eastern continental margin of North America: the Ohio Valley blizzard of January 1978, the New England blizzard of February 1978, and the Mid-Atlantic cyclone of February 1979. While medium-resolution simulations capture much of the intensification, the forecasts of the precise timing and intensity levels suffer from various degrees of error. The coastal cyclones show a 5-10 hPa dependence on the western North Atlantic sea surface temperature, which is varied within a range (± 2.5℃) compatible with interannual fluctuations. The associated vertical velocities and precipitation rates show proportionately stronger dependences on the ocean temperature perturbations. The Ohio Valley blizzard, which intensified along a track 700-800 km from the coast, shows little sensitivity to ocean temperature. The effect of a shift of - 10?latitude in the position of the snow boundary is negligible in each case. The forecasts depend strongly on the model resolution, and the coarse-resolution forecasts are consistently inferior to the medium-resolution forecasts. Studies of the corresponding sensitivities of extreme cyclonic events over eastern Asia are encouraged in order to identify characteristics that are common to numerical forecasts for the two regions.展开更多
[Objective] The research aimed to study the possible mechanism of terrain effect on cold-flow snowstorm.[Method] By using the meso-scale numerical model(WRF),a cold-flow snowstorm weather process in Shandong Peninsula...[Objective] The research aimed to study the possible mechanism of terrain effect on cold-flow snowstorm.[Method] By using the meso-scale numerical model(WRF),a cold-flow snowstorm weather process in Shandong Peninsula was carried out numerical simulation and terrain sensitivity contrast test.The possible reason of terrain effect on falling zone and strength of snowstorm was deeply analyzed from water vapor,thermodynamic field and so on.[Result] The mountain terrain in Shandong Peninsula had great influences on falling zone and strength of cold-flow snowstorm.The strength of snowstorm obviously increased,and the snowfall center obviously moved northward.The main reason was that terrain caused the low-level wind field convergence and vertical movement in the troposphere strengthened.Then,the spatial distribution of water vapor and snow water content in the cold-flow snowstorm process obviously changed.So,the whole snowstorm process was affected.[Conclusion] The mountain terrain in Shandong Peninsula was the important element which needed to be focused on considering in the forecast analysis of cold-flow snowstorm weather process.展开更多
Based on the previous statistical analysis of mesoscale convective systems(MCSs)over the second-step terrain along Yangtze-Huaihe River Valley,eight representative long-lived eastward-propagating MCSs are selected for...Based on the previous statistical analysis of mesoscale convective systems(MCSs)over the second-step terrain along Yangtze-Huaihe River Valley,eight representative long-lived eastward-propagating MCSs are selected for model-based sensitivity testing to investigate the initiation and evolution of these types of MCSs as well as their impact on downstream areas.We subject each MCS to a semi-idealized(CNTL)simulation and a sensitivity(NOLH)simulation that neglects condensational heating in the formation region.The CNTL experiment reveals convection forms in the region downstream of a shortwave trough typified by persistent southwesterly winds in the low-to midtroposphere.Upon merging with other convective systems,moist convection develops into an MCS,which propagates eastward under the influence of mid-tropospheric westerlies,and moves out of the second-step terrain.The MCS then merges with pre-existing local convection over the plains;the merged convection reinforces the cyclonic wind perturbation into a mesoscale vortex at 850 hPa.While this vortex moves eastward to regions with local vortex at 850 hPa,another vortex at 925 hPa is also intensified.Finally,the vortices at 850 and 925 hPa merge together and develop into a mesoscale convective vortex(MCV).In contrast,MCSs fail to form and move eastward in the NOLH experiment.In the absence of eastward-propagating MCSs,moist convection and mesoscale vortices still appear in the plains,but the vortex strength and precipitation intensity are significantly weakened.It is suggested the eastward-propagating MCSs over the second-step terrain significantly impact the development and enhancement of moist convection and vortices in the downstream areas.展开更多
Seasonal location and intensity changes in the western Pacific subtropical high(WPSH)are important factors dominating the synoptic weather and the distribution and magnitude of precipitation in the rain belt over East...Seasonal location and intensity changes in the western Pacific subtropical high(WPSH)are important factors dominating the synoptic weather and the distribution and magnitude of precipitation in the rain belt over East Asia.Therefore,this article delves into the forecast of the western Pacific subtropical high index during typhoon activity by adopting a hybrid deep learning model.Firstly,the predictors,which are the inputs of the model,are analysed based on three characteristics:the first is the statistical discipline of the WPSH index anomalies corresponding to the three types of typhoon paths;the second is the correspondence of distributions between sea surface temperature,850 hPa zonal wind(u),meridional wind(v),and 500 hPa potential height field;and the third is the numerical sensitivity experiment,which reflects the evident impact of variations in the physical field around the typhoon to the WPSH index.Secondly,the model is repeatedly trained through the backward propagation algorithm to predict the WPSH index using 2011–2018 atmospheric variables as the input of the training set.The model predicts the WPSH index after 6 h,24 h,48 h,and 72 h.The validation set using independent data in 2019 is utilized to illustrate the performance.Finally,the model is improved by changing the CNN2D module to the DeCNN module to enhance its ability to predict images.Taking the 2019 typhoon“Lekima”as an example,it shows the promising performance of this model to predict the 500 hPa potential height field.展开更多
There have been several recent papers on developingmovingmeshmethodsfor solving phase-field equations. However, it is observed that some of these movingmesh solutions are essentially different from the solutions on ve...There have been several recent papers on developingmovingmeshmethodsfor solving phase-field equations. However, it is observed that some of these movingmesh solutions are essentially different from the solutions on very fine fixed meshes.One of the purposes of this paper is to understand the reason for the differences. Wecarried out numerical sensitivity studies systematically in this paper and it can be concludedthat for the phase-field equations, the numerical solutions are very sensitive tothe starting mesh and the monitor function. As a separate issue, an efficient alternatingCrank-Nicolson time discretization scheme is developed for solving the nonlinearsystem resulting from a finite element approximation to the phase-field equations.展开更多
In this paper,we propose a numerical method to estimate the unknown order of a Riemann-Liouville fractional derivative for a fractional Stokes' first problem for a heated generalized second grade fluid.The implicit n...In this paper,we propose a numerical method to estimate the unknown order of a Riemann-Liouville fractional derivative for a fractional Stokes' first problem for a heated generalized second grade fluid.The implicit numerical method is employed to solve the direct problem.For the inverse problem,we first obtain the fractional sensitivity equation by means of the digamma function,and then we propose an efficient numerical method,that is,the Levenberg-Marquardt algorithm based on a fractional derivative,to estimate the unknown order of a Riemann-Liouville fractional derivative.In order to demonstrate the effectiveness of the proposed numerical method,two cases in which the measurement values contain random measurement error or not are considered.The computational results demonstrate that the proposed numerical method could efficiently obtain the optimal estimation of the unknown order of a RiemannLiouville fractional derivative for a fractional Stokes' first problem for a heated generalized second grade fluid.展开更多
Anonymized data publication has received considerable attention from the research community in recent years. For numerical sensitive attributes, most of the existing privacy-preserving data publishing techniques conce...Anonymized data publication has received considerable attention from the research community in recent years. For numerical sensitive attributes, most of the existing privacy-preserving data publishing techniques concentrate on microdata with multiple categorical sensitive attributes or only one numerical sensitive attribute. However, many real-world applications can contain multiple numerical sensitive attributes. Directly applying the existing privacy-preserving techniques for single-numerical-sensitive-attribute and multiple-categorical-sensitive- attributes often causes unexpected disclosure of private information. These techniques are particularly prone to the proximity breach, which is a privacy threat specific to numerical sensitive attributes in data publication, in this paper, we propose a privacy-preserving data publishing method, namely MNSACM, which uses the ideas of clustering and Multi-Sensitive Bucketization (MSB) to publish microdata with multiple numerical sensitive attributes. We use an example to show the effectiveness of this method in privacy protection when using multiple numerical sensitive attributes.展开更多
The spring persistent rains (SPR) over southeastern China (SEC) is a synoptic and climatic phenomenon that is unique in East Asia. Sufficient evidence proves that it results from the mechanical and thermal effects...The spring persistent rains (SPR) over southeastern China (SEC) is a synoptic and climatic phenomenon that is unique in East Asia. Sufficient evidence proves that it results from the mechanical and thermal effects of the giant Tibetan Plateau (TP), but its temporal span and spatial distribution are not clear at present. A climatological analysis of the NCEP/NCAR circulation and sensible heat data shows that at the 13th pentad of the solar year (lst pentad of March) there are remarkable increases in the sensible heating over the main and southeastern part of the TP, the southwesterly velocity over the southeastern flank of the TP and SEC, and rainfall over SEC, indicating the onset of the SPR. However, after the 27th pentad of the solar year (3rd pentad of May), these variables, except for the sensible heating over the main part of the TP, decrease rapidly. The ridge line of the subtropical high in the mid-low troposphere over the South China Sea (SCS) slopes northward to the SCS and the SCS monsoon instead of southward as before breaks out, indicating the end The rain belt center over SEC shifts of the SPR. Hence, it is reasonable to define the SPR temporal span from the 13th to 27th pentad of the solar year. Data analysis and numerical sensitivity experiments show that, although the warm and cold airs converge at about 30°N in the SPR period, the distribution and intensity of the SPR rain belt are obviously influenced by the topography of the Nanling and Wuyi Mountains (NWM). The mountains can block and lift cold and warm airs, strengthening frontogenesis and rainfall. As a result, the axis of the SPR rain belt is superposed over that of the mountain range. Accordingly, the spatial distribution of the SPR extends over most of the SEC, more specifically, to the south of the middle and lower reaches of the Yangtze River (30°N), and to the east of 110°E.展开更多
文摘A global forecast model is used to examine various sensitivities of numerical predictions of three extreme winter storms that occurred near the eastern continental margin of North America: the Ohio Valley blizzard of January 1978, the New England blizzard of February 1978, and the Mid-Atlantic cyclone of February 1979. While medium-resolution simulations capture much of the intensification, the forecasts of the precise timing and intensity levels suffer from various degrees of error. The coastal cyclones show a 5-10 hPa dependence on the western North Atlantic sea surface temperature, which is varied within a range (± 2.5℃) compatible with interannual fluctuations. The associated vertical velocities and precipitation rates show proportionately stronger dependences on the ocean temperature perturbations. The Ohio Valley blizzard, which intensified along a track 700-800 km from the coast, shows little sensitivity to ocean temperature. The effect of a shift of - 10?latitude in the position of the snow boundary is negligible in each case. The forecasts depend strongly on the model resolution, and the coarse-resolution forecasts are consistently inferior to the medium-resolution forecasts. Studies of the corresponding sensitivities of extreme cyclonic events over eastern Asia are encouraged in order to identify characteristics that are common to numerical forecasts for the two regions.
基金Supported by Special Item of Public Welfare Industry (Meteorology)Science Research (GYHY201106006)Special Item of Forecaster of China Meteorological Administration (CMATG2007Y08)Key Topics of Shandong Meteorological Bureau (2010sdqxz10)
文摘[Objective] The research aimed to study the possible mechanism of terrain effect on cold-flow snowstorm.[Method] By using the meso-scale numerical model(WRF),a cold-flow snowstorm weather process in Shandong Peninsula was carried out numerical simulation and terrain sensitivity contrast test.The possible reason of terrain effect on falling zone and strength of snowstorm was deeply analyzed from water vapor,thermodynamic field and so on.[Result] The mountain terrain in Shandong Peninsula had great influences on falling zone and strength of cold-flow snowstorm.The strength of snowstorm obviously increased,and the snowfall center obviously moved northward.The main reason was that terrain caused the low-level wind field convergence and vertical movement in the troposphere strengthened.Then,the spatial distribution of water vapor and snow water content in the cold-flow snowstorm process obviously changed.So,the whole snowstorm process was affected.[Conclusion] The mountain terrain in Shandong Peninsula was the important element which needed to be focused on considering in the forecast analysis of cold-flow snowstorm weather process.
基金supported by the National Key R&D Program of China(Grant No.2018YFC1507200)the National Natural Science Foundation of China(Grant No.41975057).
文摘Based on the previous statistical analysis of mesoscale convective systems(MCSs)over the second-step terrain along Yangtze-Huaihe River Valley,eight representative long-lived eastward-propagating MCSs are selected for model-based sensitivity testing to investigate the initiation and evolution of these types of MCSs as well as their impact on downstream areas.We subject each MCS to a semi-idealized(CNTL)simulation and a sensitivity(NOLH)simulation that neglects condensational heating in the formation region.The CNTL experiment reveals convection forms in the region downstream of a shortwave trough typified by persistent southwesterly winds in the low-to midtroposphere.Upon merging with other convective systems,moist convection develops into an MCS,which propagates eastward under the influence of mid-tropospheric westerlies,and moves out of the second-step terrain.The MCS then merges with pre-existing local convection over the plains;the merged convection reinforces the cyclonic wind perturbation into a mesoscale vortex at 850 hPa.While this vortex moves eastward to regions with local vortex at 850 hPa,another vortex at 925 hPa is also intensified.Finally,the vortices at 850 and 925 hPa merge together and develop into a mesoscale convective vortex(MCV).In contrast,MCSs fail to form and move eastward in the NOLH experiment.In the absence of eastward-propagating MCSs,moist convection and mesoscale vortices still appear in the plains,but the vortex strength and precipitation intensity are significantly weakened.It is suggested the eastward-propagating MCSs over the second-step terrain significantly impact the development and enhancement of moist convection and vortices in the downstream areas.
文摘Seasonal location and intensity changes in the western Pacific subtropical high(WPSH)are important factors dominating the synoptic weather and the distribution and magnitude of precipitation in the rain belt over East Asia.Therefore,this article delves into the forecast of the western Pacific subtropical high index during typhoon activity by adopting a hybrid deep learning model.Firstly,the predictors,which are the inputs of the model,are analysed based on three characteristics:the first is the statistical discipline of the WPSH index anomalies corresponding to the three types of typhoon paths;the second is the correspondence of distributions between sea surface temperature,850 hPa zonal wind(u),meridional wind(v),and 500 hPa potential height field;and the third is the numerical sensitivity experiment,which reflects the evident impact of variations in the physical field around the typhoon to the WPSH index.Secondly,the model is repeatedly trained through the backward propagation algorithm to predict the WPSH index using 2011–2018 atmospheric variables as the input of the training set.The model predicts the WPSH index after 6 h,24 h,48 h,and 72 h.The validation set using independent data in 2019 is utilized to illustrate the performance.Finally,the model is improved by changing the CNN2D module to the DeCNN module to enhance its ability to predict images.Taking the 2019 typhoon“Lekima”as an example,it shows the promising performance of this model to predict the 500 hPa potential height field.
基金The authors are grateful to Professor Tao Tang for many helpful discussions.The research of the first author was supported by Hong Kong Baptist University through an RGC Grant.The second author was partially supported by the National Basic Research Program of China under the grant 2005CB321701 and the Joint Applied Mathematics Research Institute between Peking University and Hong Kong Baptist University.
文摘There have been several recent papers on developingmovingmeshmethodsfor solving phase-field equations. However, it is observed that some of these movingmesh solutions are essentially different from the solutions on very fine fixed meshes.One of the purposes of this paper is to understand the reason for the differences. Wecarried out numerical sensitivity studies systematically in this paper and it can be concludedthat for the phase-field equations, the numerical solutions are very sensitive tothe starting mesh and the monitor function. As a separate issue, an efficient alternatingCrank-Nicolson time discretization scheme is developed for solving the nonlinearsystem resulting from a finite element approximation to the phase-field equations.
基金supported by the National Natural Science Foundation of China(Grants 11472161,11102102,and 91130017)the Independent Innovation Foundation of Shandong University(Grant 2013ZRYQ002)the Natural Science Foundation of Shandong Province(Grant ZR2014AQ015)
文摘In this paper,we propose a numerical method to estimate the unknown order of a Riemann-Liouville fractional derivative for a fractional Stokes' first problem for a heated generalized second grade fluid.The implicit numerical method is employed to solve the direct problem.For the inverse problem,we first obtain the fractional sensitivity equation by means of the digamma function,and then we propose an efficient numerical method,that is,the Levenberg-Marquardt algorithm based on a fractional derivative,to estimate the unknown order of a Riemann-Liouville fractional derivative.In order to demonstrate the effectiveness of the proposed numerical method,two cases in which the measurement values contain random measurement error or not are considered.The computational results demonstrate that the proposed numerical method could efficiently obtain the optimal estimation of the unknown order of a RiemannLiouville fractional derivative for a fractional Stokes' first problem for a heated generalized second grade fluid.
基金supported by the National Natural Science Foundation of China (No. 61170232)the 985 Project Funding of Sun Yat-sen University+1 种基金State Key Laboratory of Rail Traffic Control and Safety Independent Research (No. RS2012K011)Ministry of Education Funds for Innovative Groups (No. 241147529)
文摘Anonymized data publication has received considerable attention from the research community in recent years. For numerical sensitive attributes, most of the existing privacy-preserving data publishing techniques concentrate on microdata with multiple categorical sensitive attributes or only one numerical sensitive attribute. However, many real-world applications can contain multiple numerical sensitive attributes. Directly applying the existing privacy-preserving techniques for single-numerical-sensitive-attribute and multiple-categorical-sensitive- attributes often causes unexpected disclosure of private information. These techniques are particularly prone to the proximity breach, which is a privacy threat specific to numerical sensitive attributes in data publication, in this paper, we propose a privacy-preserving data publishing method, namely MNSACM, which uses the ideas of clustering and Multi-Sensitive Bucketization (MSB) to publish microdata with multiple numerical sensitive attributes. We use an example to show the effectiveness of this method in privacy protection when using multiple numerical sensitive attributes.
基金Supported by the National "973" program under Grant No.2006CB403600the National Natural Science Foundation of China under Grant Nos.40475027,40220503,and 40523001
文摘The spring persistent rains (SPR) over southeastern China (SEC) is a synoptic and climatic phenomenon that is unique in East Asia. Sufficient evidence proves that it results from the mechanical and thermal effects of the giant Tibetan Plateau (TP), but its temporal span and spatial distribution are not clear at present. A climatological analysis of the NCEP/NCAR circulation and sensible heat data shows that at the 13th pentad of the solar year (lst pentad of March) there are remarkable increases in the sensible heating over the main and southeastern part of the TP, the southwesterly velocity over the southeastern flank of the TP and SEC, and rainfall over SEC, indicating the onset of the SPR. However, after the 27th pentad of the solar year (3rd pentad of May), these variables, except for the sensible heating over the main part of the TP, decrease rapidly. The ridge line of the subtropical high in the mid-low troposphere over the South China Sea (SCS) slopes northward to the SCS and the SCS monsoon instead of southward as before breaks out, indicating the end The rain belt center over SEC shifts of the SPR. Hence, it is reasonable to define the SPR temporal span from the 13th to 27th pentad of the solar year. Data analysis and numerical sensitivity experiments show that, although the warm and cold airs converge at about 30°N in the SPR period, the distribution and intensity of the SPR rain belt are obviously influenced by the topography of the Nanling and Wuyi Mountains (NWM). The mountains can block and lift cold and warm airs, strengthening frontogenesis and rainfall. As a result, the axis of the SPR rain belt is superposed over that of the mountain range. Accordingly, the spatial distribution of the SPR extends over most of the SEC, more specifically, to the south of the middle and lower reaches of the Yangtze River (30°N), and to the east of 110°E.