A variational method is developed to retrieve winds in the first step and then thermodynamic fields in the second step from Doppler radar observations. In the first step, wind fields are retrieved at two time levels: ...A variational method is developed to retrieve winds in the first step and then thermodynamic fields in the second step from Doppler radar observations. In the first step, wind fields are retrieved at two time levels: the beginning and ending times of the data assimilation period, simultaneously from two successive volume scans by using the weak form constraints provided by the mass continuity and vorticity equations. As the retrieved wind fields are expressed by Legendre polynomial expansions at the beginning and ending times, the time tendency term in the vorticity equation can be conveniently formulated, and the retrieved winds can be compared with the radar observed radial winds in the cost function at the precise time and position of each radar beam. In the second step, the perturbation pressure and temperature fields at the middle time are then derived from the retrieved wind fields and the velocity time tendency by using the weak form constraints provided by the three momentum equations. The merits of the new method are demonstrated by numerical experiments with simulated radar observations and compared with the traditional least squares methods which consider neither the precise observation times and positions nor the velocity time tendency. The new method is also applied to real radar data for a heavy rainfall event during the 2001 Meiyu season in China.展开更多
This paper addresses joint wind-wave induced dynamic responses of a semi-type offshore floating wind turbine（OFWT） under normal states and fault event conditions. The analysis in this paper is conducted in time doma...This paper addresses joint wind-wave induced dynamic responses of a semi-type offshore floating wind turbine（OFWT） under normal states and fault event conditions. The analysis in this paper is conducted in time domain, using an aero-hydro-servo-elastic simulation code-FAST. Owing to the unique viscous features of the reference system, the original viscous damping model implemented in FAST is replaced with a quadratic one to gain an accurate capture of viscous effects. Simulation cases involve free-decay motion in still water, steady motions in the presence of regular waves and wind as well as dynamic response in operational sea states with and without wind. Simulations also include the cases for transient responses induced by fast blade pitching after emergency shutdown. The features of platform motions, local structural loads and a typical mooring line tension force under a variety of excitations are obtained and investigated.展开更多
We present a comparison of changes in large and sharp solar wind dynamic pressure, observed by several spacecraft, with fast disturbances in the magnetospheric magnetic field, measured by the geosynchronous satellites...We present a comparison of changes in large and sharp solar wind dynamic pressure, observed by several spacecraft, with fast disturbances in the magnetospheric magnetic field, measured by the geosynchronous satellites. More than 260 changes in solar wind pressure during the period 1996-2003 are selected for this study. Large statistics show that an increase （a decrease） in dynamic pressure always results in an increase （a decrease） in the magnitude of geosynchronous magnetic field. The amplitude of response to the geomagnetic field strongly depends on the location of observer relative to the noon meridian, the value of pressure before disturbance, and the change in amplitude of pressure.展开更多
The complexity of the loads acting on the offshore wind turbines （OWl＇s） structures and the significance of investigation on structure dynamics are explained. Test results obtained from a scaled wind turbine model ...The complexity of the loads acting on the offshore wind turbines （OWl＇s） structures and the significance of investigation on structure dynamics are explained. Test results obtained from a scaled wind turbine model are also summarized. The model is supported on monopile, subjected to different types of dynamic loading using an innovative out of balance mass system to apply cyclic/dynamic loads. The test results show the natural frequency of the wind turbine structure increases with the number of cycles, but with a reduced rate of increase with the accumulation of soil strain level. The change is found to be dependent on the shear strain level in the soil next to the pile which matches with the expectations from the element tests of the soil. The test results were plotted in a non-dimensional manner in order to be scaled to predict the orototvoe conseouences usin~ element tests of a soil usin~ resonant column aoDararus.展开更多
Using surface and balloon-sounding measurements, satellite retrievals, and ERA5 reanalysis during 2011–20, this study compares the precipitation and related wind dynamics, moisture and heat features in different area...Using surface and balloon-sounding measurements, satellite retrievals, and ERA5 reanalysis during 2011–20, this study compares the precipitation and related wind dynamics, moisture and heat features in different areas of the South China Sea(SCS) before and after SCS summer monsoon onset(SCSSMO). The rainy sea around Dongsha(hereafter simply referred to as Dongsha) near the north coast, and the rainless sea around Xisha(hereafter simply referred to as Xisha) in the western SCS, are selected as two typical research subregions. It is found that Dongsha, rather than Xisha, has an earlier and greater increase in precipitation after SCSSMO under the combined effect of strong low-level southwesterly winds, coastal terrain blocking and lifting, and northern cold air. When the 950-h Pa southwesterly winds enhance and advance northward, accompanied by strengthened moisture flux, there is a strong convergence of wind and moisture in Dongsha due to a sudden deceleration and rear-end collision of wind by coastal terrain blocking. Moist and warm advection over Dongsha enhances early and deepens up to 200 h Pa in association with the strengthened upward motion after SCSSMO, thereby providing ample moisture and heat to form strong precipitation. However, when the 950-h Pa southwesterly winds weaken and retreat southward, Xisha is located in a wind-break area where strong convergence and upward motion centers move in. The vertical moistening and heating by advection in Xisha enhance later and appear far weaker compared to that in Dongsha, consistent with later and weaker precipitation.展开更多
We carried out a wind tunnel test to measure cladding loads for a high-rise building of 295 m in height, which would be located in the business center of Chongqing Municipality, P. R. China. The rigid model was used t...We carried out a wind tunnel test to measure cladding loads for a high-rise building of 295 m in height, which would be located in the business center of Chongqing Municipality, P. R. China. The rigid model was used to determine fluctuating local pressures on the exterior surfaces of the building. The wind tunnel test results show the cr/tical zone of wind pressures on building surfaces in both standalone and interference conditions. The computational fluid dynamics （CFD） was conducted by using the FLUENT Code to compare with the wind tunnel test results, and the steady three-dimensional turbulent flow with Realizable k-ε as a turbulence model was used. The CFD results are agree with the wind tunnel test results in regards to distributions of wind pressures over a high-rise building＇s surfaces.展开更多
The state-of-art Computational Fluid Dynamics （CFD） codes FLUENT is applied in a fine-scale simulation of the wind field over a complex terrain. Several numerical tests are performed to validate the capability of FL...The state-of-art Computational Fluid Dynamics （CFD） codes FLUENT is applied in a fine-scale simulation of the wind field over a complex terrain. Several numerical tests are performed to validate the capability of FLUENT on describing the wind field details over a complex terrain. The results of the numerical tests show that FLUENT can simulate the wind field over extremely complex terrain, which cannot be simulated by mesoscale models. The reason why FLUENT can cope with extremely complex terrain, which can not be coped with by mesoscale models, relies on some particular techniques adopted by FLUENT, such as computer-aided design （CAD） technique, unstructured grid technique and finite volume method. Compared with mesoscale models, FLUENT can describe terrain in much more accurate details and can provide wind simulation results with higher resolution and more accuracy.展开更多
Studies on soil wind erosion began with single factors affecting soil wind erosion; with increasing quantities of data being accumulated,the wind erosion equation(WEQ),the revised wind erosion equation(RWEQ),the wind ...Studies on soil wind erosion began with single factors affecting soil wind erosion; with increasing quantities of data being accumulated,the wind erosion equation(WEQ),the revised wind erosion equation(RWEQ),the wind erosion prediction system(WEPS),and other soil wind erosion models have been successively established,and great advances have been achieved.Here we briefly review the soil wind erosion research course and analyze the advantages and disadvantages of the current soil wind erosion models.From the perspective of the dynamics of wind erosion,we classified the factors affecting soil wind erosion into three categories,namely,wind erosivity factors(WEF),soil antierodibility factors(SAF),and roughness interference factors(RIF).We proposed the concept of a standard plot of soil wind erosion to solve the problem of uncertainty of the soil wind erosion modulus on a spatial scale,and provided methods to set similarity conditions in wind tunnel simulation experiments and to convert the spatial scale of the wind erosion modulus from the standard plot to a large scale field.We also proposed a conceptual model on the basis of the dynamics of soil wind erosion with the theoretical basis that wind produces a shear force on the soil surface.This shear force is partitioned by barely erodible soil surfaces and roughness elements on the ground,and the amount of soil loss by wind should be calculated by comparing the shear force of the wind on barely erodible soil surfaces with the anti-erosion force of the surface soil.One advantage of this conceptual model is that the calculated soil wind erosion modulus is not subject to changes of spatial scale.Finally,we recommended continual improvement of the existing models while also establishing new models.展开更多
This study reports the rare ultralow-frequency(ULF) wave activity associated with the solar wind dynamic pressure enhancement that was successively observed by the GOES-17(Geostationary Operational Environmental Satel...This study reports the rare ultralow-frequency(ULF) wave activity associated with the solar wind dynamic pressure enhancement that was successively observed by the GOES-17(Geostationary Operational Environmental Satellite) in the magnetosphere, the CSES(China Seismo-Electromagnetic Satellite) in the ionosphere, and the THEMIS ground-based observatories(GBO) GAKO and EAGL in the Earth's polar region during the main phase of an intense storm on 4 November 2021. Along with the enhanced-pressure solar wind moving tailward, the geomagnetic field structure experienced a large-scale change. From dawn/dusk sides to midnight, the GAKO, EAGL, and GOES-17 sequentially observed the ULF waves in a frequency range of0.04–0.36 Hz at L shells of ~5.07, 6.29, and 5.67, respectively. CSES also observed the ULF wave event with the same frequency ranges at wide L-shells of 2.52–6.22 in the nightside ionosphere. The analysis results show that the ULF waves at ionospheric altitude were mixed toroidal-poloidal mode waves. Comparing the ULF waves observed in different regions, we infer that the nightside ULF waves were directly or indirectly excited by the solar wind dynamic pressure increase: in the area of L-shells~2.52–6.29, the magnetic field line resonances(FLRs) driven by the solar wind dynamic pressure increase is an essential excitation source;on the other hand, around L~3.29, the ULF waves can also be excited by the outward expansion of the plasmapause owing to the decrease of the magnetospheric convection, and in the region of L-shells ~5.19–6.29, the ULF waves are also likely excited by the ion cyclotron instabilities driven by the solar wind dynamic pressure increase.展开更多
An example of post-noon ionospheric absorption observed by the imaging riometers at Ny-Alesund / Danmarkshavn in the arctic region and Zhongshan Station in Antarctic is presented. The post-noon absorption observed sim...An example of post-noon ionospheric absorption observed by the imaging riometers at Ny-Alesund / Danmarkshavn in the arctic region and Zhongshan Station in Antarctic is presented. The post-noon absorption observed simultaneously between the hemispherical stations was a spike-type with weak intensity (<1 dB) during the high solar wind dynamic pressure. The absorption spikes might be caused by precipitation of highrenergy electrons (30 - 300 keV) in the closed dayside magnetosphere. It should be noted that the precipitation region of the absorption spike associated with the steep pressure increase (~ 13 nPa) was localized and shifted equatorward.展开更多
With coordinated observations of the NOAA 15 satellite and OUL magnetometer station in Finland, we report that the elec- tromagnetic ion cyclotron （EMIC） waves which were stimulated by the compression of the magneto...With coordinated observations of the NOAA 15 satellite and OUL magnetometer station in Finland, we report that the elec- tromagnetic ion cyclotron （EMIC） waves which were stimulated by the compression of the magnetosphere drive relativistic electron precipitation in geoquiescence on 1 Jan 2007. After an enhancement of solar wind dynamic pressure （SWDP）, a day- side Pcl pulsation was observed by the OUL station. Such a Pcl pulsation is caused by an EMIC wave which propagates from the generation source to lower altitudes. Simultaneously, the NOAA 15 satellite registered an enhancement of precipitating electron count rates with energies 〉3 MeV within the anisotropic zone of protons. This phenomenon is coincident with the quasi-linear theoretical calculation presented in this paper. Our observations suggest that after a positive impulse of solar wind, the compression-related EMIC waves can drive relativistic electrons precipitation and play a pivotal role in the dynamic of ra- diation belts.展开更多
Background:Baseline levels of tree mortality can,over time,contribute to high snag densities and high levels of deadwood(down woody debris)if fire is infrequent and decomposition is slow.Deadwood can be important for ...Background:Baseline levels of tree mortality can,over time,contribute to high snag densities and high levels of deadwood(down woody debris)if fire is infrequent and decomposition is slow.Deadwood can be important for tree recruitment,and it plays a major role in terrestrial carbon cycling,but deadwood is rarely examined in a spatially explicit context.Methods:Between 2011 and 2019,we annually tracked all trees and snags≥1 cm in diameter and mapped all pieces of deadwood≥10 cm diameter and≥1 m in length in 25.6 ha of Tsuga heterophylla/Pseudotsuga menziesii forest.We analyzed the amount,biomass,and spatial distribution of deadwood,and we assessed how various causes of mortality that contributed uniquely to deadwood creation.Results:Compared to aboveground woody live biomass of 481 Mg ha^(−1)(from trees≥10 cm diameter),snag biomass was 74 Mg ha^(−1) and deadwood biomass was 109 Mg ha^(−1)(from boles≥10 cm diameter).Biomass from large-diameter trees(≥60 cm)accounted for 85%,88%,and 58%,of trees,snags,and deadwood,respectively.Total aboveground woody live and dead biomass was 668 Mg ha^(−1).The annual production of downed wood(≥10 cm diameter)from tree boles averaged 4 Mg ha^(−1) yr^(−1).Woody debris was spatially heterogeneous,varying more than two orders of magnitude from 4 to 587 Mg ha^(−1) at the scale of 20 m×20 m quadrats.Almost all causes of deadwood creation varied in importance between large-diameter trees and small-diameter trees.Biomass of standing stems and deadwood had weak inverse distributions,reflecting the long period of time required for trees to reach large diameters following antecedent tree mortalities and the centennial scale time required for deadwood decomposition.Conclusion:Old-growth forests contain large stores of biomass in living trees,as well as in snag and deadwood biomass pools that are stable long after tree death.Ignoring biomass(or carbon)in deadwood pools can lead to substantial underestimations of sequestration and stability.展开更多
文摘A variational method is developed to retrieve winds in the first step and then thermodynamic fields in the second step from Doppler radar observations. In the first step, wind fields are retrieved at two time levels: the beginning and ending times of the data assimilation period, simultaneously from two successive volume scans by using the weak form constraints provided by the mass continuity and vorticity equations. As the retrieved wind fields are expressed by Legendre polynomial expansions at the beginning and ending times, the time tendency term in the vorticity equation can be conveniently formulated, and the retrieved winds can be compared with the radar observed radial winds in the cost function at the precise time and position of each radar beam. In the second step, the perturbation pressure and temperature fields at the middle time are then derived from the retrieved wind fields and the velocity time tendency by using the weak form constraints provided by the three momentum equations. The merits of the new method are demonstrated by numerical experiments with simulated radar observations and compared with the traditional least squares methods which consider neither the precise observation times and positions nor the velocity time tendency. The new method is also applied to real radar data for a heavy rainfall event during the 2001 Meiyu season in China.
基金financially supported by the National Natural Science Foundation of China(Grant No.51239007)
文摘This paper addresses joint wind-wave induced dynamic responses of a semi-type offshore floating wind turbine（OFWT） under normal states and fault event conditions. The analysis in this paper is conducted in time domain, using an aero-hydro-servo-elastic simulation code-FAST. Owing to the unique viscous features of the reference system, the original viscous damping model implemented in FAST is replaced with a quadratic one to gain an accurate capture of viscous effects. Simulation cases involve free-decay motion in still water, steady motions in the presence of regular waves and wind as well as dynamic response in operational sea states with and without wind. Simulations also include the cases for transient responses induced by fast blade pitching after emergency shutdown. The features of platform motions, local structural loads and a typical mooring line tension force under a variety of excitations are obtained and investigated.
基金Project supported by the Russian Foundation for Basic Researches （Grant Nos 04-02-16152 and 04-02-39004）, the International Association for the Promotion of Co-operation with Scientists from the New Independent States of the Former Soviet Union （Grant Nos 03-51-3738 and MK-2267.2004.2） and the National Natural Science Foundation of China （Grand Nos 40325010 and 40574069）.
文摘We present a comparison of changes in large and sharp solar wind dynamic pressure, observed by several spacecraft, with fast disturbances in the magnetospheric magnetic field, measured by the geosynchronous satellites. More than 260 changes in solar wind pressure during the period 1996-2003 are selected for this study. Large statistics show that an increase （a decrease） in dynamic pressure always results in an increase （a decrease） in the magnitude of geosynchronous magnetic field. The amplitude of response to the geomagnetic field strongly depends on the location of observer relative to the noon meridian, the value of pressure before disturbance, and the change in amplitude of pressure.
基金supported by the National Natural Science Foundation of China(51109184,51209183,and 51325901)
文摘The complexity of the loads acting on the offshore wind turbines （OWl＇s） structures and the significance of investigation on structure dynamics are explained. Test results obtained from a scaled wind turbine model are also summarized. The model is supported on monopile, subjected to different types of dynamic loading using an innovative out of balance mass system to apply cyclic/dynamic loads. The test results show the natural frequency of the wind turbine structure increases with the number of cycles, but with a reduced rate of increase with the accumulation of soil strain level. The change is found to be dependent on the shear strain level in the soil next to the pile which matches with the expectations from the element tests of the soil. The test results were plotted in a non-dimensional manner in order to be scaled to predict the orototvoe conseouences usin~ element tests of a soil usin~ resonant column aoDararus.
基金supported by a Guangdong Major Project of Basic and Applied Basic Research (Grant No.2020B0301030004)the Collaborative Observation and Multisource Real-time Data Fusion and Analysis Technology & Innovation team (Grant No.GRMCTD202103)the Foshan Special Project on Science and Technology in Social Field (Grant No.2120001008761)。
文摘Using surface and balloon-sounding measurements, satellite retrievals, and ERA5 reanalysis during 2011–20, this study compares the precipitation and related wind dynamics, moisture and heat features in different areas of the South China Sea(SCS) before and after SCS summer monsoon onset(SCSSMO). The rainy sea around Dongsha(hereafter simply referred to as Dongsha) near the north coast, and the rainless sea around Xisha(hereafter simply referred to as Xisha) in the western SCS, are selected as two typical research subregions. It is found that Dongsha, rather than Xisha, has an earlier and greater increase in precipitation after SCSSMO under the combined effect of strong low-level southwesterly winds, coastal terrain blocking and lifting, and northern cold air. When the 950-h Pa southwesterly winds enhance and advance northward, accompanied by strengthened moisture flux, there is a strong convergence of wind and moisture in Dongsha due to a sudden deceleration and rear-end collision of wind by coastal terrain blocking. Moist and warm advection over Dongsha enhances early and deepens up to 200 h Pa in association with the strengthened upward motion after SCSSMO, thereby providing ample moisture and heat to form strong precipitation. However, when the 950-h Pa southwesterly winds weaken and retreat southward, Xisha is located in a wind-break area where strong convergence and upward motion centers move in. The vertical moistening and heating by advection in Xisha enhance later and appear far weaker compared to that in Dongsha, consistent with later and weaker precipitation.
基金Funded by the National Natural Science Foundation of China(No.90715024)
文摘We carried out a wind tunnel test to measure cladding loads for a high-rise building of 295 m in height, which would be located in the business center of Chongqing Municipality, P. R. China. The rigid model was used to determine fluctuating local pressures on the exterior surfaces of the building. The wind tunnel test results show the cr/tical zone of wind pressures on building surfaces in both standalone and interference conditions. The computational fluid dynamics （CFD） was conducted by using the FLUENT Code to compare with the wind tunnel test results, and the steady three-dimensional turbulent flow with Realizable k-ε as a turbulence model was used. The CFD results are agree with the wind tunnel test results in regards to distributions of wind pressures over a high-rise building＇s surfaces.
基金supported by the National Natural Science Foundation of China(40805004, 40705039 and 90715031)the "Mini-projecton detailed survey and evaluation of wind energy resources"supported by National Climate Center of Chinese Meteoro-logical Administration (CWERA2010002)
文摘The state-of-art Computational Fluid Dynamics （CFD） codes FLUENT is applied in a fine-scale simulation of the wind field over a complex terrain. Several numerical tests are performed to validate the capability of FLUENT on describing the wind field details over a complex terrain. The results of the numerical tests show that FLUENT can simulate the wind field over extremely complex terrain, which cannot be simulated by mesoscale models. The reason why FLUENT can cope with extremely complex terrain, which can not be coped with by mesoscale models, relies on some particular techniques adopted by FLUENT, such as computer-aided design （CAD） technique, unstructured grid technique and finite volume method. Compared with mesoscale models, FLUENT can describe terrain in much more accurate details and can provide wind simulation results with higher resolution and more accuracy.
基金supported by the National Natural Science Foundation of China(Grant No.41330746)
文摘Studies on soil wind erosion began with single factors affecting soil wind erosion; with increasing quantities of data being accumulated,the wind erosion equation(WEQ),the revised wind erosion equation(RWEQ),the wind erosion prediction system(WEPS),and other soil wind erosion models have been successively established,and great advances have been achieved.Here we briefly review the soil wind erosion research course and analyze the advantages and disadvantages of the current soil wind erosion models.From the perspective of the dynamics of wind erosion,we classified the factors affecting soil wind erosion into three categories,namely,wind erosivity factors(WEF),soil antierodibility factors(SAF),and roughness interference factors(RIF).We proposed the concept of a standard plot of soil wind erosion to solve the problem of uncertainty of the soil wind erosion modulus on a spatial scale,and provided methods to set similarity conditions in wind tunnel simulation experiments and to convert the spatial scale of the wind erosion modulus from the standard plot to a large scale field.We also proposed a conceptual model on the basis of the dynamics of soil wind erosion with the theoretical basis that wind produces a shear force on the soil surface.This shear force is partitioned by barely erodible soil surfaces and roughness elements on the ground,and the amount of soil loss by wind should be calculated by comparing the shear force of the wind on barely erodible soil surfaces with the anti-erosion force of the surface soil.One advantage of this conceptual model is that the calculated soil wind erosion modulus is not subject to changes of spatial scale.Finally,we recommended continual improvement of the existing models while also establishing new models.
基金supported by the National Key Research and Development Program of China (Grant No. 2023YFE0117300)the National Natural Science Foundation of China (Grant No. 4187417)the APSCO Earthquake Research Project Phase Ⅱ, and the Dragon 5 Cooperation 2020-2024 (Grant No. 59236)。
文摘This study reports the rare ultralow-frequency(ULF) wave activity associated with the solar wind dynamic pressure enhancement that was successively observed by the GOES-17(Geostationary Operational Environmental Satellite) in the magnetosphere, the CSES(China Seismo-Electromagnetic Satellite) in the ionosphere, and the THEMIS ground-based observatories(GBO) GAKO and EAGL in the Earth's polar region during the main phase of an intense storm on 4 November 2021. Along with the enhanced-pressure solar wind moving tailward, the geomagnetic field structure experienced a large-scale change. From dawn/dusk sides to midnight, the GAKO, EAGL, and GOES-17 sequentially observed the ULF waves in a frequency range of0.04–0.36 Hz at L shells of ~5.07, 6.29, and 5.67, respectively. CSES also observed the ULF wave event with the same frequency ranges at wide L-shells of 2.52–6.22 in the nightside ionosphere. The analysis results show that the ULF waves at ionospheric altitude were mixed toroidal-poloidal mode waves. Comparing the ULF waves observed in different regions, we infer that the nightside ULF waves were directly or indirectly excited by the solar wind dynamic pressure increase: in the area of L-shells~2.52–6.29, the magnetic field line resonances(FLRs) driven by the solar wind dynamic pressure increase is an essential excitation source;on the other hand, around L~3.29, the ULF waves can also be excited by the outward expansion of the plasmapause owing to the decrease of the magnetospheric convection, and in the region of L-shells ~5.19–6.29, the ULF waves are also likely excited by the ion cyclotron instabilities driven by the solar wind dynamic pressure increase.
文摘An example of post-noon ionospheric absorption observed by the imaging riometers at Ny-Alesund / Danmarkshavn in the arctic region and Zhongshan Station in Antarctic is presented. The post-noon absorption observed simultaneously between the hemispherical stations was a spike-type with weak intensity (<1 dB) during the high solar wind dynamic pressure. The absorption spikes might be caused by precipitation of highrenergy electrons (30 - 300 keV) in the closed dayside magnetosphere. It should be noted that the precipitation region of the absorption spike associated with the steep pressure increase (~ 13 nPa) was localized and shifted equatorward.
基金supported by the National Natural Science Foundation of China(Grant Nos.41374168,41174140,41174147 and 41004060)the Research Fund for the Doctoral Program of Higher Education of China(Grant No.20110141110043)the Fundamental Research Funds for the Central Universities of China(Grant No.2012212020204)
文摘With coordinated observations of the NOAA 15 satellite and OUL magnetometer station in Finland, we report that the elec- tromagnetic ion cyclotron （EMIC） waves which were stimulated by the compression of the magnetosphere drive relativistic electron precipitation in geoquiescence on 1 Jan 2007. After an enhancement of solar wind dynamic pressure （SWDP）, a day- side Pcl pulsation was observed by the OUL station. Such a Pcl pulsation is caused by an EMIC wave which propagates from the generation source to lower altitudes. Simultaneously, the NOAA 15 satellite registered an enhancement of precipitating electron count rates with energies 〉3 MeV within the anisotropic zone of protons. This phenomenon is coincident with the quasi-linear theoretical calculation presented in this paper. Our observations suggest that after a positive impulse of solar wind, the compression-related EMIC waves can drive relativistic electrons precipitation and play a pivotal role in the dynamic of ra- diation belts.
基金Funding was received from the Utah Agricultural Experiment Station(projects 1153,1398,and 1423 to JAL)the National Science Foundation(DEB#1542681 to JAL and colleagues)the Smithsonian Institution ForestGEO.Research was performed under a 5-year permit(2016–2020)from the USDA Forest Service Pacific Northwest Research Station.
文摘Background:Baseline levels of tree mortality can,over time,contribute to high snag densities and high levels of deadwood(down woody debris)if fire is infrequent and decomposition is slow.Deadwood can be important for tree recruitment,and it plays a major role in terrestrial carbon cycling,but deadwood is rarely examined in a spatially explicit context.Methods:Between 2011 and 2019,we annually tracked all trees and snags≥1 cm in diameter and mapped all pieces of deadwood≥10 cm diameter and≥1 m in length in 25.6 ha of Tsuga heterophylla/Pseudotsuga menziesii forest.We analyzed the amount,biomass,and spatial distribution of deadwood,and we assessed how various causes of mortality that contributed uniquely to deadwood creation.Results:Compared to aboveground woody live biomass of 481 Mg ha^(−1)(from trees≥10 cm diameter),snag biomass was 74 Mg ha^(−1) and deadwood biomass was 109 Mg ha^(−1)(from boles≥10 cm diameter).Biomass from large-diameter trees(≥60 cm)accounted for 85%,88%,and 58%,of trees,snags,and deadwood,respectively.Total aboveground woody live and dead biomass was 668 Mg ha^(−1).The annual production of downed wood(≥10 cm diameter)from tree boles averaged 4 Mg ha^(−1) yr^(−1).Woody debris was spatially heterogeneous,varying more than two orders of magnitude from 4 to 587 Mg ha^(−1) at the scale of 20 m×20 m quadrats.Almost all causes of deadwood creation varied in importance between large-diameter trees and small-diameter trees.Biomass of standing stems and deadwood had weak inverse distributions,reflecting the long period of time required for trees to reach large diameters following antecedent tree mortalities and the centennial scale time required for deadwood decomposition.Conclusion:Old-growth forests contain large stores of biomass in living trees,as well as in snag and deadwood biomass pools that are stable long after tree death.Ignoring biomass(or carbon)in deadwood pools can lead to substantial underestimations of sequestration and stability.
