The near-Earth asteroid collisions could cause catastrophic disasters to humanity and the Earth,so it is crucial to monitor asteroids.Ground-based synthetic aperture radar(SAR)is an observation technique for high reso...The near-Earth asteroid collisions could cause catastrophic disasters to humanity and the Earth,so it is crucial to monitor asteroids.Ground-based synthetic aperture radar(SAR)is an observation technique for high resolution imaging of asteroids.The ground-based SAR requires a long integration time to achieve a large synthetic aperture,and the echo signal will be seriously affected by temporal-spatial variant troposphere.Traditional spatiotemporal freezing tropospheric models are ineffective.To cope with this,this paper models and analyses the impacts of temporal-spatial variant troposphere on ground-based SAR imaging of asteroids.For the background tropo-sphere,a temporal-spatial variant ray tracing method is proposed to trace the 4D(3D spatial+temporal)refractive index network provided by the numerical weather model,and calculate the error of the background troposphere.For the tropospheric turbulence,the Andrew power spectral model is used in conjunction with multiphase screen theory,and varying errors are obtained by tracking the changing position of the pierce point on the phase screen.Through simulation,the impact of temporal-spatial variant tropospheric errors on image quality is analyzed,and the simulation results show that the X-band echo signal is seriously affected by the troposphere and the echo signal must be compensated.展开更多
This article summarizes the researches on the middle and upper atmosphere by Chinese scientists in 2010-2012.The focuses are placed on the advances in construction of ground-based remote sensing facilities,the mean st...This article summarizes the researches on the middle and upper atmosphere by Chinese scientists in 2010-2012.The focuses are placed on the advances in construction of ground-based remote sensing facilities,the mean state and long-term changes in the middle atmosphere circulation, the prevailing dynamical processes,and the coupling of the middle atmospheric layers.展开更多
This paper presents estimation of tropospheric scintillation based on ITU-R model from previous 10 years meteorological data.Scintillation As(p) is critical in designing of microwave links for achieving optimal perfor...This paper presents estimation of tropospheric scintillation based on ITU-R model from previous 10 years meteorological data.Scintillation As(p) is critical in designing of microwave links for achieving optimal performance.There are many phenomenons that cause degradation to signal during transmission through the earth's atmosphere one of them is scintillation.Scintillation estimation is based on measurements of surface temperature T and relative humidity RH.Input parameter for ITU-R scintillation estimation model is the monthly average of wet part of refractivity Nwet.MATLAB software tool is employed to show the results for tropospheric scintillation in various seasons for time percentage p and frequencies ranging from 4GHz to 20 GHz.展开更多
Several theories have been developed to explain tropical biennial oscillation （TBO）, as an air-sea interactive system to impact Asian and global weather and climate, and some models have been established to produce ...Several theories have been developed to explain tropical biennial oscillation （TBO）, as an air-sea interactive system to impact Asian and global weather and climate, and some models have been established to produce a TBO. A simple 5-box model, with almost all the key processes associated with TBO, can produce a TBO by including airsea interactions in the monsoon regions. Despite that, the South China Sea/western North Pacific summer monsoon （SCS/WNPSM）, a very important monsoon subsystem, is neglected. In this paper, based on the dynamical framework of 5-box model, the term of SCS/WNPSM has been added and a 6-box model has been developed. Comparing the difference of TBO sensibilities with several key parameters, air-sea coupling coefficient α, SST-thermocline feedback coefficient γand wind-evaporation feedback coefficient λ, between the modified model and original model, TBO is more sensible to the parameters in the new model. The results imply that the eastern Pacific and local wind-evaporation play more important roles in the TBO when including SCS /WNPSM.展开更多
The observed tropospheric biennial oscillation （TBO） in the western North Pacific （WNP） monsoon region has an interdecadal variability with a period of 40-50 yr. That suggests a weaker effect of the TBO on the Eas...The observed tropospheric biennial oscillation （TBO） in the western North Pacific （WNP） monsoon region has an interdecadal variability with a period of 40-50 yr. That suggests a weaker effect of the TBO on the East Asia followed by a stronger one. A simple analytic model was designed to investigate the mechanism of the interdecadal variability of the TBO. The results indicated that a local TBO air-sea system not only supports the TBO variability in the WNP monsoon region but also produces an interdecadal variability of the TBO.展开更多
The maritime tropospheric duct is a low-altitude anomalous refractivity structure over the ocean surface,and it can significantly affect the performance of many shore-based/shipboard radar and communication systems.We...The maritime tropospheric duct is a low-altitude anomalous refractivity structure over the ocean surface,and it can significantly affect the performance of many shore-based/shipboard radar and communication systems.We propose the idea that maritime tropospheric ducts can be retrieved from ocean forward-scattered low-elevation global positioning system（GPS） signals.Retrieval is accomplished by matching the measured power patterns of the signals to those predicted by the forward propagation model as a function of the modified refractivity profile.On the basis of a parabolic equation method and bistatic radar equation,we develop such a forward model for computing the trapped propagation characteristics of an ocean forward-scattered GPS signal within a tropospheric duct.A new GPS scattering initial field is defined for this model to start the propagation modeling.A preliminary test on the performance of this model is conducted using measured data obtained from a 2009-experiment in the South China Sea.Results demonstrate that this model can predict GPS propagation characteristics within maritime tropospheric ducts and serve as a forward model for duct inversion.展开更多
Japanese larch(Larix kaempferi(Lamb.)Carr.)and its hybrid are economically important coniferous trees widely grown in the Northern Hemisphere.Ground-level ozone(O_(3))concentrations have increased since the preindustr...Japanese larch(Larix kaempferi(Lamb.)Carr.)and its hybrid are economically important coniferous trees widely grown in the Northern Hemisphere.Ground-level ozone(O_(3))concentrations have increased since the preindustrial era,and research projects showed that Japanese larch is susceptible to elevated O_(3)exposures.Therefore,methodologies are needed to(1)protect Japanese larch against O_(3)damage and(2)conduct biomonitoring of O_(3)in Japanese larch forests and,thus,monitor O_(3)risks to Japanese larch.For the first time,this study evaluates whether the synthetic chemical ethylenediurea(EDU)can protect Japanese larch against O_(3)damage,in two independent experiments.In the first experiment,seedling communities,simulating natural regeneration,were treated with EDU(0,100,200,and 400 mg L^(-1))and exposed to either ambient or elevated O_(3)in a growing season.In the second experiment,individually-grown saplings were treated with EDU(0,200 and 400 mg L-1)and exposed to ambient O_(3)in two growing seasons and to elevated O_(3)in the succeeding two growing seasons.The two experiments revealed that EDU concentrations of 200-400 mg L^(-1)could protect Japanese larch seedling communities and individual saplings against O_(3)-induced inhibition of growth and productivity.However,EDU concentrations≤200 mg L^(-1)did offer only partial protection when seedling communities were coping with higher level of O_(3)-induced stress,and only 400 mg EDU L^(-1)fully protected communities under higher stress.Therefore,we conclude that among the concentrations tested the concentration offering maximum protection to Japanese larch plants under high competition and O_(3)-induced stress is that of 400 mg EDU L^(-1).The results of this study can provide a valuable resource of information for applied forestry in an O_(3)-polluted world.展开更多
Ground-level ozone(O_(3))pollution is a persistent environmental issue that can lead to adverse effects on trees and wood production,thus indicating a need for forestry interventions to mediate O_(3) effects.We treate...Ground-level ozone(O_(3))pollution is a persistent environmental issue that can lead to adverse effects on trees and wood production,thus indicating a need for forestry interventions to mediate O_(3) effects.We treated hybrid larch(Larix gmelinii var.japonica×L.kaempferi)saplings grown in nutrient-poor soils with 0 or 400 mg L^(-1) water solutions of the antiozonant ethylenediurea(EDU0,EDU400)and exposed them to ambient O_(3)(AOZ;08:00-18:00≈30 nmol mol^(-1)) or elevated O_(3)(EOZ;08:00-18:00≈60 nmol mol^(-1))over three growing seasons.We found that EDU400 protected saplings against most effects of EOZ,which included extensive visible foliar injury,premature senescence,decreased photosynthetic pigment contents and altered balance between pigments,suppressed gas exchange and biomass production,and impaired leaf litter decay.While EOZ had limited effects on plant growth(suppressed stem diameter),it decreased the total number of buds per plant,an effect that was not observed in the first growing season.These results indicate that responses to EOZ might have implications to plant competitiveness,in the long term,as a result of decreased potential for vegetative growth.However,when buds were standardized per unit of branches biomass,EOZ significantly increased the number of buds per unit of biomass,suggesting a potentially increased investment to bud development,in an effort to enhance growth potential and competitiveness in the next growing season.EDU400 minimized most of these effects of EOZ,significantly enhancing plant health under O_(3)-induced stress.The effect of EDU was attributed mainly to a biochemical mode of action.Therefore,hybrid larch,which is superior to its parents,can be significantly improved by EDU under long-term elevated O_(3) exposure,providing a perspective for enhancing afforestation practices.展开更多
Tropospheric Scattering(Troposcatter) and Tropospheric Ducting are two different mechanisms due to in-homogenoueties in the lower part of the Earths atmosphere.Their common influence in propagation of microwaves is st...Tropospheric Scattering(Troposcatter) and Tropospheric Ducting are two different mechanisms due to in-homogenoueties in the lower part of the Earths atmosphere.Their common influence in propagation of microwaves is studied here in order to achieve a feasible naval communication system.Although not new,Troposcatter together with Tropospheric Ducting communications are regaining popularity in current military and civil applications such as isolated islands and oil extraction facilities in the open sea.The innovation proposed here is the application of such systems in naval communications where at least one of the stations is mobile.Several propagation together with fading models are simulated using appropriate programs and scientific simulation packets in order to predict maximum range of such communication systems in each dominant mode of operation.Then appropriate antenna design proposals are given to overcome the high propagation loss and minimize possible interferences.展开更多
In Europe,tropospheric ozone pollution appears as a major air quality issue,and ozone concentrations remain potentially harmful to vegetation.In this study we compared the trends of two ozone metrics widely used for f...In Europe,tropospheric ozone pollution appears as a major air quality issue,and ozone concentrations remain potentially harmful to vegetation.In this study we compared the trends of two ozone metrics widely used for forests protection in Europe,the AOT40(Accumulated Ozone over Threshold of 40 ppb)which only depends on surface air ozone concentrations,and the Phytotoxic Ozone Dose which is the accumulated ozone uptake through stomata over the growing season,and above a threshold Y of uptake(PODY).By using a chemistry transport model,we found that European-averaged ground-level ozone concentrations(−2%)and AOT40 metric(−26.5%)significantly declined from 2000 to 2014,due to successful control strategies to reduce the emission of ozone precursors in Europe since the early 1990s.In contrast,the stomatal ozone uptake by forests increased from 17.5 to 26.6 mmol O3 m^(−2)despite the reduction in ozone concentrations,leading to an increase of potential ozone damage on plants in Europe.In a climate change context,a biologically-sound stomatal flux-based standard(PODY)as new European legislative standard is needed.展开更多
Eucalypts are important forest resources in southwestern China,and may be tolerant to elevated ground-level ozone(O3)concentrations that can negatively affect plant growth.High CO2 may offset O3-induced effects by pro...Eucalypts are important forest resources in southwestern China,and may be tolerant to elevated ground-level ozone(O3)concentrations that can negatively affect plant growth.High CO2 may offset O3-induced effects by providing excess carbon to produce secondary metabolites or by inducing stomatal closure.Here,the effects of elevated CO2 and O3 on leaf secondary metabolites and other defense chemicals were studied by exposing seedlings of Eucalyptus globulus,E.grandis,and E.camaldulensis×E.deglupta to a factorial combination of two levels of O3(<10 nmol mol^(−1)and 60 nmol mol^(−1))and CO2(ambient:370μmol mol^(−1)and 600μmol mol^(−1))in open-top field chambers.GC-profiles of leaf extracts illustrated the effect of elevated O3 and the countering effect of high CO2 on compounds in leaf epicuticular wax and essential oils,i.e.,n-icosane,geranyl acetate and elixene,compounds known as a first-line defense against insect herbivores.n-Icosane may be involved in tolerance mechanisms of E.grandis and the hybrid,while geranyl acetate and elixene in the tolerance of E.globulus.Elevated O3 and CO2,singly or in combination,affected only leaf physiology but not biomass of various organs.Elevated CO2 impacted several leaf traits,including stomatal conductance,leaf mass per area,carbon,lignin,n-icosane,geranyl acetate and elixene.Limited effects of elevated O3 on leaf physiology(nitrogen,n-icosane,geranyl acetate,elixene)were commonly offset by elevated CO2.We conclude that E.globulus,E.grandis and the hybrid were tolerant to these O3 and CO2 treatments,and n-icosane,geranyl acetate and elixene may be major players in tolerance mechanisms of the tested species.展开更多
With the rapid development of the fifth-generation(5 G)mobile communication technology,the application of each frequency band has reached the extreme,causing mutual interference between different modules.Hence,there i...With the rapid development of the fifth-generation(5 G)mobile communication technology,the application of each frequency band has reached the extreme,causing mutual interference between different modules.Hence,there is a requirement for detecting filtering and preventing interference.In the troposphere,over-the-horizon propagation occurs in atmospheric ducts and turbulent media.The effects of both ducting and turbulence can increase the probability of occurrence of long-distance co-channel interference(CCI),in turn,severely affecting the key performance indicators such as system access,handover and drop.In the 5 G era,to ensure communication channels and information security,CCI must be reduced.This paper introduces a scattering parabolic equation algorithm for calculating signal propagation in atmospheric ducts on irregular terrain boundaries.It combines Hitney’s radio physical optical model and Wagner’s nonuniform turbulent scattering model for calculating the tropospheric scattering in an evaporation duct or a surface-based duct.The new model proposes a tropospheric scattering parabolic equation algorithm for various tropospheric duct environments.Finally,as a specific case,the topographical boundaries between several cities in the East China Plain were considered,and the over-the-horizon propagation loss was simulated for various ducting and turbulent environments.The simulation results were used to evaluate whether CCI would occur between cities in a specific environment.展开更多
Ground-level ozone(O_(3)) is a widespread air pollutant causing extensive injuries in plants.However,its effects on perennial energy crops remain poorly under-stood due to technical difficulties in cultivating fast-gr...Ground-level ozone(O_(3)) is a widespread air pollutant causing extensive injuries in plants.However,its effects on perennial energy crops remain poorly under-stood due to technical difficulties in cultivating fast-growing shrubs for biomass production under O_(3) treatment on the field.Here we present the results of a two-year evaluation in the framework of which willow(Salix sachalinensis F.Schmid)shrubs were exposed to ambient(AOZ)or elevated(EOZ)O_(3) in two successive growing seasons(2014,2015)and treated with 0(EDU0)or 400 mg L^(−1)(EDU400)eth-ylenediurea spray in the second growing season.In 2014,EOZ altered the chemical composition of both top young and fallen leaves,and a novel mechanism of decreasing Mg in fallen leaves while highly enriching it in young top leaves was revealed in shrubs exposed to EOZ.In 2015,EDU400 alleviated EOZ-induced decreases in leaf fresh mass to dry mass ratio(FM/DM)and leaf mass per area(LMA).While EDU400 protected against EOZ-induced suppression of the maximum rate at which leaves can fix carbon(A_(max))in O_(3)-asymptomatic leaves,it did not alle-viate EOZ-induced suppression of the maximum rates of carboxylation(VCmax)and electron transport(J_(max))and chlorophylls a,b,and a+b in the same type of leaves.In O_(3)-symptomatic leaves,however,EDU400 alleviated EOZ-induced suppression of chlorophylls a and a+b,indicating different mode of action of EDU between O_(3)-asymptomatic and O_(3)-symptomatic leaves.Extensive herbivory occurred only in AOZ-exposed plants,leading to suppressed biomass production,while EOZ also led to a similar suppression of biomass production(EDU0×EOZ vs.EDU400×EOZ).In 2016,carry-over effects were also evaluated following cropping and transplantation into new ambient plots.Effects of EOZ in the preceding growing seasons extended to the third growing season in the form of suppressed ratoon biomass production,indicating carry-over effect of EOZ.Although EDU400 protected against EOZ-induced suppression of biomass production when applied in 2015,there was no carry-over effect of EDU in the absence of EDU treatment in 2016.The results of this study provide novel mechanistic understandings of O_(3)and EDU modes of action and can enlighten cultivation of willow as energy crop.展开更多
An airborne multi-axis differential optical absorption spectroscopic （AMAX-DOAS） instrument was developed and applied to measure tropospheric NO2 in the Pearl River Delta region in the south of China. By combining t...An airborne multi-axis differential optical absorption spectroscopic （AMAX-DOAS） instrument was developed and applied to measure tropospheric NO2 in the Pearl River Delta region in the south of China. By combining the measurements in nadir and zenith directions and analyzing the UV and visible spectral region using the DOAS method, information about tropospheric NO2 vertical columns was obtained. Strong tropospheric NO2 signals were detected when flying over heavilly polluted regions and point sources like plants. The AMAX-DOAS results were compared with ground-based MAX-DOAS observations in the southwest of Zhuhai city using the same parameters for radiative transport calculations. The difference in vertical column data between the two instruments is about 8%. Our data were also compared with those from OMI and fair agreement was obtained with a correlation coefficient R of 0.61. The difference between the two instruments can be attributed to the different spatial resolution and the temporal mismatch during the measurements.展开更多
基金supported in part by the National Natural Science Foundation of China(Nos.62101039,62201051)in part by the Shandong Excellent Young Scientists Fund Program(Overseas)in part by China Postdoctoral Science Foundation(No.2022M720443).
文摘The near-Earth asteroid collisions could cause catastrophic disasters to humanity and the Earth,so it is crucial to monitor asteroids.Ground-based synthetic aperture radar(SAR)is an observation technique for high resolution imaging of asteroids.The ground-based SAR requires a long integration time to achieve a large synthetic aperture,and the echo signal will be seriously affected by temporal-spatial variant troposphere.Traditional spatiotemporal freezing tropospheric models are ineffective.To cope with this,this paper models and analyses the impacts of temporal-spatial variant troposphere on ground-based SAR imaging of asteroids.For the background tropo-sphere,a temporal-spatial variant ray tracing method is proposed to trace the 4D(3D spatial+temporal)refractive index network provided by the numerical weather model,and calculate the error of the background troposphere.For the tropospheric turbulence,the Andrew power spectral model is used in conjunction with multiphase screen theory,and varying errors are obtained by tracking the changing position of the pierce point on the phase screen.Through simulation,the impact of temporal-spatial variant tropospheric errors on image quality is analyzed,and the simulation results show that the X-band echo signal is seriously affected by the troposphere and the echo signal must be compensated.
文摘This article summarizes the researches on the middle and upper atmosphere by Chinese scientists in 2010-2012.The focuses are placed on the advances in construction of ground-based remote sensing facilities,the mean state and long-term changes in the middle atmosphere circulation, the prevailing dynamical processes,and the coupling of the middle atmospheric layers.
文摘This paper presents estimation of tropospheric scintillation based on ITU-R model from previous 10 years meteorological data.Scintillation As(p) is critical in designing of microwave links for achieving optimal performance.There are many phenomenons that cause degradation to signal during transmission through the earth's atmosphere one of them is scintillation.Scintillation estimation is based on measurements of surface temperature T and relative humidity RH.Input parameter for ITU-R scintillation estimation model is the monthly average of wet part of refractivity Nwet.MATLAB software tool is employed to show the results for tropospheric scintillation in various seasons for time percentage p and frequencies ranging from 4GHz to 20 GHz.
基金Project supported by the National Natural Science Foundation of China （Grant No 40505019） and the 0pen Research Fund of Laboratory of China Meteorological Administration （Grant No CMATG2006L03）.
文摘Several theories have been developed to explain tropical biennial oscillation （TBO）, as an air-sea interactive system to impact Asian and global weather and climate, and some models have been established to produce a TBO. A simple 5-box model, with almost all the key processes associated with TBO, can produce a TBO by including airsea interactions in the monsoon regions. Despite that, the South China Sea/western North Pacific summer monsoon （SCS/WNPSM）, a very important monsoon subsystem, is neglected. In this paper, based on the dynamical framework of 5-box model, the term of SCS/WNPSM has been added and a 6-box model has been developed. Comparing the difference of TBO sensibilities with several key parameters, air-sea coupling coefficient α, SST-thermocline feedback coefficient γand wind-evaporation feedback coefficient λ, between the modified model and original model, TBO is more sensible to the parameters in the new model. The results imply that the eastern Pacific and local wind-evaporation play more important roles in the TBO when including SCS /WNPSM.
基金supported by the National Natural Science Foundation of China (Grant No 40505019)
文摘The observed tropospheric biennial oscillation （TBO） in the western North Pacific （WNP） monsoon region has an interdecadal variability with a period of 40-50 yr. That suggests a weaker effect of the TBO on the East Asia followed by a stronger one. A simple analytic model was designed to investigate the mechanism of the interdecadal variability of the TBO. The results indicated that a local TBO air-sea system not only supports the TBO variability in the WNP monsoon region but also produces an interdecadal variability of the TBO.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61172031 and 41175012)
文摘The maritime tropospheric duct is a low-altitude anomalous refractivity structure over the ocean surface,and it can significantly affect the performance of many shore-based/shipboard radar and communication systems.We propose the idea that maritime tropospheric ducts can be retrieved from ocean forward-scattered low-elevation global positioning system（GPS） signals.Retrieval is accomplished by matching the measured power patterns of the signals to those predicted by the forward propagation model as a function of the modified refractivity profile.On the basis of a parabolic equation method and bistatic radar equation,we develop such a forward model for computing the trapped propagation characteristics of an ocean forward-scattered GPS signal within a tropospheric duct.A new GPS scattering initial field is defined for this model to start the propagation modeling.A preliminary test on the performance of this model is conducted using measured data obtained from a 2009-experiment in the South China Sea.Results demonstrate that this model can predict GPS propagation characteristics within maritime tropospheric ducts and serve as a forward model for duct inversion.
基金supported in part by Research Grant#201802 of the Forestry and Forest Products Research Instituteby KAKENHI Grant Number JP17F17102 of the Japan Society for the Promotion of Science(JSPS)。
文摘Japanese larch(Larix kaempferi(Lamb.)Carr.)and its hybrid are economically important coniferous trees widely grown in the Northern Hemisphere.Ground-level ozone(O_(3))concentrations have increased since the preindustrial era,and research projects showed that Japanese larch is susceptible to elevated O_(3)exposures.Therefore,methodologies are needed to(1)protect Japanese larch against O_(3)damage and(2)conduct biomonitoring of O_(3)in Japanese larch forests and,thus,monitor O_(3)risks to Japanese larch.For the first time,this study evaluates whether the synthetic chemical ethylenediurea(EDU)can protect Japanese larch against O_(3)damage,in two independent experiments.In the first experiment,seedling communities,simulating natural regeneration,were treated with EDU(0,100,200,and 400 mg L^(-1))and exposed to either ambient or elevated O_(3)in a growing season.In the second experiment,individually-grown saplings were treated with EDU(0,200 and 400 mg L-1)and exposed to ambient O_(3)in two growing seasons and to elevated O_(3)in the succeeding two growing seasons.The two experiments revealed that EDU concentrations of 200-400 mg L^(-1)could protect Japanese larch seedling communities and individual saplings against O_(3)-induced inhibition of growth and productivity.However,EDU concentrations≤200 mg L^(-1)did offer only partial protection when seedling communities were coping with higher level of O_(3)-induced stress,and only 400 mg EDU L^(-1)fully protected communities under higher stress.Therefore,we conclude that among the concentrations tested the concentration offering maximum protection to Japanese larch plants under high competition and O_(3)-induced stress is that of 400 mg EDU L^(-1).The results of this study can provide a valuable resource of information for applied forestry in an O_(3)-polluted world.
基金partly supported by grant#201802 of the Japan’s Forestry and Forest Products Research Institute(FFPRI)KAKENHI grant#JP17F17102 of the Japan Society for the Promotion of Science(JSPS).E.A.support from The Startup Foundation for Introducing Talent of Nanjing University of Information Science&Technology(NUIST),Nanjing,China(Grant No.003080)。
文摘Ground-level ozone(O_(3))pollution is a persistent environmental issue that can lead to adverse effects on trees and wood production,thus indicating a need for forestry interventions to mediate O_(3) effects.We treated hybrid larch(Larix gmelinii var.japonica×L.kaempferi)saplings grown in nutrient-poor soils with 0 or 400 mg L^(-1) water solutions of the antiozonant ethylenediurea(EDU0,EDU400)and exposed them to ambient O_(3)(AOZ;08:00-18:00≈30 nmol mol^(-1)) or elevated O_(3)(EOZ;08:00-18:00≈60 nmol mol^(-1))over three growing seasons.We found that EDU400 protected saplings against most effects of EOZ,which included extensive visible foliar injury,premature senescence,decreased photosynthetic pigment contents and altered balance between pigments,suppressed gas exchange and biomass production,and impaired leaf litter decay.While EOZ had limited effects on plant growth(suppressed stem diameter),it decreased the total number of buds per plant,an effect that was not observed in the first growing season.These results indicate that responses to EOZ might have implications to plant competitiveness,in the long term,as a result of decreased potential for vegetative growth.However,when buds were standardized per unit of branches biomass,EOZ significantly increased the number of buds per unit of biomass,suggesting a potentially increased investment to bud development,in an effort to enhance growth potential and competitiveness in the next growing season.EDU400 minimized most of these effects of EOZ,significantly enhancing plant health under O_(3)-induced stress.The effect of EDU was attributed mainly to a biochemical mode of action.Therefore,hybrid larch,which is superior to its parents,can be significantly improved by EDU under long-term elevated O_(3) exposure,providing a perspective for enhancing afforestation practices.
文摘Tropospheric Scattering(Troposcatter) and Tropospheric Ducting are two different mechanisms due to in-homogenoueties in the lower part of the Earths atmosphere.Their common influence in propagation of microwaves is studied here in order to achieve a feasible naval communication system.Although not new,Troposcatter together with Tropospheric Ducting communications are regaining popularity in current military and civil applications such as isolated islands and oil extraction facilities in the open sea.The innovation proposed here is the application of such systems in naval communications where at least one of the stations is mobile.Several propagation together with fading models are simulated using appropriate programs and scientific simulation packets in order to predict maximum range of such communication systems in each dominant mode of operation.Then appropriate antenna design proposals are given to overcome the high propagation loss and minimize possible interferences.
基金carried out with the contribution of the LIFE financial instrument of the European Union in the framework of the MOTTLES project“Monitoring ozone injury for setting new critical levels”(LIFE15 ENV/IT/000183).
文摘In Europe,tropospheric ozone pollution appears as a major air quality issue,and ozone concentrations remain potentially harmful to vegetation.In this study we compared the trends of two ozone metrics widely used for forests protection in Europe,the AOT40(Accumulated Ozone over Threshold of 40 ppb)which only depends on surface air ozone concentrations,and the Phytotoxic Ozone Dose which is the accumulated ozone uptake through stomata over the growing season,and above a threshold Y of uptake(PODY).By using a chemistry transport model,we found that European-averaged ground-level ozone concentrations(−2%)and AOT40 metric(−26.5%)significantly declined from 2000 to 2014,due to successful control strategies to reduce the emission of ozone precursors in Europe since the early 1990s.In contrast,the stomatal ozone uptake by forests increased from 17.5 to 26.6 mmol O3 m^(−2)despite the reduction in ozone concentrations,leading to an increase of potential ozone damage on plants in Europe.In a climate change context,a biologically-sound stomatal flux-based standard(PODY)as new European legislative standard is needed.
基金supported by a Grant-in-Aid for Scientific Researches(Nos.21114008,23380078)JST Grant(No.JPMJSC18HB)the RA-GCOE project.
文摘Eucalypts are important forest resources in southwestern China,and may be tolerant to elevated ground-level ozone(O3)concentrations that can negatively affect plant growth.High CO2 may offset O3-induced effects by providing excess carbon to produce secondary metabolites or by inducing stomatal closure.Here,the effects of elevated CO2 and O3 on leaf secondary metabolites and other defense chemicals were studied by exposing seedlings of Eucalyptus globulus,E.grandis,and E.camaldulensis×E.deglupta to a factorial combination of two levels of O3(<10 nmol mol^(−1)and 60 nmol mol^(−1))and CO2(ambient:370μmol mol^(−1)and 600μmol mol^(−1))in open-top field chambers.GC-profiles of leaf extracts illustrated the effect of elevated O3 and the countering effect of high CO2 on compounds in leaf epicuticular wax and essential oils,i.e.,n-icosane,geranyl acetate and elixene,compounds known as a first-line defense against insect herbivores.n-Icosane may be involved in tolerance mechanisms of E.grandis and the hybrid,while geranyl acetate and elixene in the tolerance of E.globulus.Elevated O3 and CO2,singly or in combination,affected only leaf physiology but not biomass of various organs.Elevated CO2 impacted several leaf traits,including stomatal conductance,leaf mass per area,carbon,lignin,n-icosane,geranyl acetate and elixene.Limited effects of elevated O3 on leaf physiology(nitrogen,n-icosane,geranyl acetate,elixene)were commonly offset by elevated CO2.We conclude that E.globulus,E.grandis and the hybrid were tolerant to these O3 and CO2 treatments,and n-icosane,geranyl acetate and elixene may be major players in tolerance mechanisms of the tested species.
基金supported by the National Natural Science Foundation of China(Grant Nos.62005205,62071359,and 61775175)Natural Science Basic Research Program of Shaanxi,China(Grant No.2020JQ-331)。
文摘With the rapid development of the fifth-generation(5 G)mobile communication technology,the application of each frequency band has reached the extreme,causing mutual interference between different modules.Hence,there is a requirement for detecting filtering and preventing interference.In the troposphere,over-the-horizon propagation occurs in atmospheric ducts and turbulent media.The effects of both ducting and turbulence can increase the probability of occurrence of long-distance co-channel interference(CCI),in turn,severely affecting the key performance indicators such as system access,handover and drop.In the 5 G era,to ensure communication channels and information security,CCI must be reduced.This paper introduces a scattering parabolic equation algorithm for calculating signal propagation in atmospheric ducts on irregular terrain boundaries.It combines Hitney’s radio physical optical model and Wagner’s nonuniform turbulent scattering model for calculating the tropospheric scattering in an evaporation duct or a surface-based duct.The new model proposes a tropospheric scattering parabolic equation algorithm for various tropospheric duct environments.Finally,as a specific case,the topographical boundaries between several cities in the East China Plain were considered,and the over-the-horizon propagation loss was simulated for various ducting and turbulent environments.The simulation results were used to evaluate whether CCI would occur between cities in a specific environment.
基金supported by grant#201802 of the Japan’s Forestry and Forest Products Research Institute(FFPRI)KAKENHI grant#JP17F17102 of the Japan Society for the Promotion of Science(JSPS)+2 种基金Evgenios Agathokleous was an International Research Fellow(ID No:P17102)the JSPS,and JSPS is a non-profit,independent administrative institutionE.A acknowl-edges multi-year support from The Startup Foundation for Introducing Talent of Nanjing University of Information Science&Technology(NUIST),Nanjing,China(Grant No.003080).
文摘Ground-level ozone(O_(3)) is a widespread air pollutant causing extensive injuries in plants.However,its effects on perennial energy crops remain poorly under-stood due to technical difficulties in cultivating fast-growing shrubs for biomass production under O_(3) treatment on the field.Here we present the results of a two-year evaluation in the framework of which willow(Salix sachalinensis F.Schmid)shrubs were exposed to ambient(AOZ)or elevated(EOZ)O_(3) in two successive growing seasons(2014,2015)and treated with 0(EDU0)or 400 mg L^(−1)(EDU400)eth-ylenediurea spray in the second growing season.In 2014,EOZ altered the chemical composition of both top young and fallen leaves,and a novel mechanism of decreasing Mg in fallen leaves while highly enriching it in young top leaves was revealed in shrubs exposed to EOZ.In 2015,EDU400 alleviated EOZ-induced decreases in leaf fresh mass to dry mass ratio(FM/DM)and leaf mass per area(LMA).While EDU400 protected against EOZ-induced suppression of the maximum rate at which leaves can fix carbon(A_(max))in O_(3)-asymptomatic leaves,it did not alle-viate EOZ-induced suppression of the maximum rates of carboxylation(VCmax)and electron transport(J_(max))and chlorophylls a,b,and a+b in the same type of leaves.In O_(3)-symptomatic leaves,however,EDU400 alleviated EOZ-induced suppression of chlorophylls a and a+b,indicating different mode of action of EDU between O_(3)-asymptomatic and O_(3)-symptomatic leaves.Extensive herbivory occurred only in AOZ-exposed plants,leading to suppressed biomass production,while EOZ also led to a similar suppression of biomass production(EDU0×EOZ vs.EDU400×EOZ).In 2016,carry-over effects were also evaluated following cropping and transplantation into new ambient plots.Effects of EOZ in the preceding growing seasons extended to the third growing season in the form of suppressed ratoon biomass production,indicating carry-over effect of EOZ.Although EDU400 protected against EOZ-induced suppression of biomass production when applied in 2015,there was no carry-over effect of EDU in the absence of EDU treatment in 2016.The results of this study provide novel mechanistic understandings of O_(3)and EDU modes of action and can enlighten cultivation of willow as energy crop.
基金supported by the National Natural Science Foundation of China(Grant Nos.41275037,41275038,and 41275027)
文摘An airborne multi-axis differential optical absorption spectroscopic （AMAX-DOAS） instrument was developed and applied to measure tropospheric NO2 in the Pearl River Delta region in the south of China. By combining the measurements in nadir and zenith directions and analyzing the UV and visible spectral region using the DOAS method, information about tropospheric NO2 vertical columns was obtained. Strong tropospheric NO2 signals were detected when flying over heavilly polluted regions and point sources like plants. The AMAX-DOAS results were compared with ground-based MAX-DOAS observations in the southwest of Zhuhai city using the same parameters for radiative transport calculations. The difference in vertical column data between the two instruments is about 8%. Our data were also compared with those from OMI and fair agreement was obtained with a correlation coefficient R of 0.61. The difference between the two instruments can be attributed to the different spatial resolution and the temporal mismatch during the measurements.
