Extreme weather events pose an ever-greater threat to people,infrastructure,and nature.Forest ecosystems are highly sensitive to extreme cold events that can disrupt ecosystem functions,especially in montane regions.I...Extreme weather events pose an ever-greater threat to people,infrastructure,and nature.Forest ecosystems are highly sensitive to extreme cold events that can disrupt ecosystem functions,especially in montane regions.Ice storms can be particularly destructive,with rapid ice accretion causing tree branches to break,even snapping or uprooting entire trees.In March 2022,the Shennongjia forest in central China experienced severe ice storm conditions that severely damaged over 230,300ha.We utilized this opportunity to assess the vulnerability of different tree types(coniferous,deciduous,and evergreen broad-leaved)and stand compositions to damage resulting from ice glaze along an elevation gradient from 1,200 to 2,400m a.s.l.Among the 7,144 trees surveyed,10.1%suffered some extent of damage,which was most prolific in the middle elevation zone.While 96.8%of all damage occurred to deciduous broadleaved trees that dominated the forest community,the most severe damage(uprooting and lower trunk breakage)occurred to coniferous trees.The extent and severity of tree damage were moderated by forest composition,with secondary effects of forest structure and slope.Abiotic factors predominantly affected coniferous trees.We emphasize that more research and monitoring are needed to better understand the full impact of extreme weather events on forests,especially as the frequency and intensity of these events increases due to climate change.展开更多
Cunninghamia lanceolata （Lamb.） Hook. is economically the most important tree species in southern China and has been cultivated in plantations on a large scale. This species is widely used in construction, furniture...Cunninghamia lanceolata （Lamb.） Hook. is economically the most important tree species in southern China and has been cultivated in plantations on a large scale. This species is widely used in construction, furniture, utensils and shipbuilding. Soil fertility of C. lanceolata stands affects soil structure, porosity and nutrient availability, which causes changes in fauna activity. During January to February 2008, an ice storm caused extensive damage to C. lanceolata stands. Despite the environmental importance of soil fauna, basic information on the distribution and diversity of soil fauna in C. lanceolata stands after ice storm damage is lacking. To assess the response of soil fauna diversity and distribution to forest gaps following the ice storm, five small gaps （each 30-40 m^2）, five large gaps （each 80-100 m^2） and five canopy cover plots were selected within a 2-ha C. lanceolata stand. Soil samples were collected from 0 to 10 cm depth in March 2011 to measure soil fauna diversity and abundance. The abundance and community composition of the soil fauna varied with gap size. In canopy cover sites, the number of individuals was 2.0 and 5.2 times greater than in the small gaps and large gaps. Three taxa （Nematoda, Oribatida and lnsecta） of soil inver- tebrates occurred commonly, and Nematoda dominated the communities in all three habitat types. The Shannon-Wiener diversity index, Margalef diversity index, and Pielou evenness index were high in the small gaps, indicating that they harbored the most species, with the most even distribution, and the highest diversity. Our results indicated that gap size apparently affected abundance and community composition of the soil fauna.展开更多
Ice storms,as important sources of frequent and injurious disturbances,drive forest dynamics in the Northern Hemisphere.However,stand-level differential vulnerability to ice storms and the associated factors that pred...Ice storms,as important sources of frequent and injurious disturbances,drive forest dynamics in the Northern Hemisphere.However,stand-level differential vulnerability to ice storms and the associated factors that predispose forest stands remain unclear.This is particularly concerning in the subtropics where the frequency of ice storms is predicted to increase with global warming.Here we assessed how the impact on three forest stands(early and late secondary-growth forests,and old-growth forests)differed after an extreme ice storm during 20–21 March 2022,and identified the abiotic and biotic factors that determine the damage intensity in the Shennongjia World Natural Heritage Site,a biodiversity conservation hotspot in central China.We found a stand-specific‘middomain effect’where the late secondary-growth forest sustained the most severe damage,the early secondarygrowth forest sustained the least,and the old-growth forest suffered an intermediate amount.‘Crown broken’was the most severe damage type across all three forest stands,although the proportion of‘branch broken’was also high in the old-growth forest.Topography played a significant role in determining the vulnerability of the early secondary-growth forest to severe ice storms whereas the forest structure and composition were important factors in explaining the damage rates in the old-growth forest,although they differed among the damage categories.In contrast,topography,forest structure and composition generally explain the intensity of damage in the late secondary-growth forests.Our results highlight that,in subtropical forests,the intensity of damage caused by severe ice storms and related determining factors are stand-level dependent.We also suggest exploring potential management strategies(e.g.,slow-growing hardwood species that can resist storms should be the main species for reforestation in early secondary-growth forests)to mitigate the risk of future severe ice storms,as well as other wind-related climatic extremes.展开更多
Ice storms can cause substantial damage to tree crowns and lead to growth reduction.However,in uneven-aged stands,the growth of an individual tree may also increase due to crown release caused by the damage or mortali...Ice storms can cause substantial damage to tree crowns and lead to growth reduction.However,in uneven-aged stands,the growth of an individual tree may also increase due to crown release caused by the damage or mortality of neighboring trees.Three years after the devastating ice storm in 2014 in mixed uneven-aged Dinaric forests(Croatia),we cored 156 European beech(Fagus sylvatica)and 85 silver fir(Abies alba)trees across 20 permanent sample plots to study the post-storm growth response as a function of tree,stand,site,spatial arrangement and local competition factors.The ice storm damaged over 84% of trees on the sampled plots.Among the cored trees,52.7% exhibited growth reduction,which on average amounted to3.1%relative to the pre-disturbance average.Trees with less than 40% crown damage maintained their pre-disturbance growth rates or experienced only minor growth suppression.While 60% of beech trees suffered a growth reduction at an average rate of 7.2%,the average radial increment of fir after the storm was 14.0% higher compared to the pre-storm rate.A linear mixedeffects model suggests that the growth response can largely be explained by the focal and neighboring tree species identity,tree competition pressure,focal and neighboring tree damage,crown size,slenderness index and stoniness.Growth release was positively associated with fir,inverse distance-weighted crown damage of the nearest neighbor,shorter crowns,slenderness,less stony sites and less damaged trees.The analysis suggests that at the same level of local competition load,trees with a broadleaved and damaged nearest neighbor are more likely to experience growth release than those with a coniferous or undamaged nearest neighbor.This implies that unevenaged stands with a substantial presence and mingling of both conifers and broadleaves are expected to be more resilient to ice storms and are less likely to suffer growth reduction.展开更多
Assessing forest loss from snow and ice storms is vital for disaster evaluation and sustainable management.Traditional optical remote sensing methods,which focus on horizontal canopy changes,struggle to capture vertic...Assessing forest loss from snow and ice storms is vital for disaster evaluation and sustainable management.Traditional optical remote sensing methods,which focus on horizontal canopy changes,struggle to capture vertical stand alterations caused by snow and ice storms.This study introduces the LiDAR Forest Structure Change Index(LFSCI),a novel index that employs bitemporal unmanned aerial vehicle(UAV)LiDAR point data to comprehensively evaluate changes in the vertical distribution of forest stands.Following ice storms in Shi-zishan,Wuhan,China in early 2024,research was conducted to compare the performance of LFSCI with tradi-tional metrics,such as canopy cover(CC),Leaf Area Index(LAI),and tree height(TH),across two spatial scales(grid and individual tree).LFSCI was evaluated at nine point densities(5-177 pt/m^(2)).Through validation with field-measured stand volume changes from 43 plots,LFSCI showed superior correlation(R^(2)=0.64 for grids,0.59 for trees)in comparison to CC(R^(2)=0.52),LAI(R^(2)=0.38),and TH(R^(2)=0.16).Higher point densities enhanced accuracy,with 50 pt/m^(2) recommended for effective snow and ice storm impact detection.Pure broad-leaved forests were more susceptible to loss in comparison to mixed conifer-broadleaf forests,mixed broadleaf for-ests,and needle forests.Additionally,stands characterized by greater tree heights,steeper slopes,and shaded conditions were more vulnerable to damage than those in other environments.展开更多
This paper proposes a co-optimal strategy using line hardening,mobile devices(mobile ice-melting device,mobile emergency generator,mobile energy storage system),and repair crew dispatching to improve distribution syst...This paper proposes a co-optimal strategy using line hardening,mobile devices(mobile ice-melting device,mobile emergency generator,mobile energy storage system),and repair crew dispatching to improve distribution system resilience during ice storms.A multi-stage defender-attacker-defender model is established to take into account interactions and coupling relationships between different measures.In our proposed model,ice storms will attack the distribution and transportation system in a worst-case scenario,affecting system performance from various perspectives.Corresponding to the different operating states in the distribution system affected by ice storms,aiming at minimizing the weighted load shedding value,this paper applies various measures to different stages to improve the response and defense capabilities to ice storms and realize restoration of the distribution system ultimately.The nested column-and-constraint generation algorithm is used to solve the model efficiently.The effectiveness of the proposed model and solution method for enhancing the distribution system resilience is verified on the modified IEEE 33-bus distribution system and modified realworld zone of Caracas 141-bus distribution system.展开更多
Between January and February 2008,a severe ice storm occurred in southern China.The storm damaged nearly 21 million hectares of forest lands with broken branch,trunk breakage,and stem bending of many trees.This natura...Between January and February 2008,a severe ice storm occurred in southern China.The storm damaged nearly 21 million hectares of forest lands with broken branch,trunk breakage,and stem bending of many trees.This natural disturbance provides a unique opportunity to study impacts of extreme climatic event on forest birds.Using hierarchical multi-species occupancy model(species richness;27 species)and N-mixture model(abundance;3 species),we investigated how the storm affected resident bird species in subtropical forest in southern China.We sampled birds at Chebaling National Nature Reserve in Guangdong Province,monthly for 1 year each before and after the storm by mist nets.To take into account variations in temperature between years and between months,we incorporated monthly mean temperature into the models as an additional covariate.Observed species richness was greater before the storm.Estimated species richness(from the hierarchical model)also tended to be greater before than after the storm although 95%Bayesian credible intervals of these estimates were overlapped.Temperature showed a negative effect on estimated species richness,indicating greater species richness during winter.Among three species captured the most,abundance of Chestnut Bulbul(Hemixos castanonotus)significantly decreased after the storm.Other two species,Grey Treepie(Dendrocitta formosae)and Huet’s Fulvetta(Alcippe hueti)showed insignificant responses to the storm.Our study indicates that the 2008 ice storm may not have a significant impact on species richness of resident birds in subtropical forest;however,the effect can be species-specific and negative to some species’population.展开更多
Icicles are often formed under the downside surface of conductor in the wet growth icing of overhead power line.When the ice deposit around overhead power line is molten by Joule heat produced by current,the pattern o...Icicles are often formed under the downside surface of conductor in the wet growth icing of overhead power line.When the ice deposit around overhead power line is molten by Joule heat produced by current,the pattern of heat transfer of ice deposit with icicles is dissimilar to that without icicle,so the ice-melting model for the columnar icing conductor cannot be applied to icicle-shaped icing conductor.According to the heat-transfer characteristic of the icicle-shaped icing conductor,this paper puts forward a DC ice-melting model for the icicle-shaped icing conductor.Because this full model includes three-dimensional heat-transfer and interface movement,which cannot be solved in closed form,a finite element scheme in space-domain and a finite difference scheme in time-domain are employed to discretize the governing equations.Firstly the whole ice-melting process on the icicle-shaped icing conductor is simulated by this model.Then the simulated results are validated by ice-melting experiments in the artificial chamber.The study from the model and the experiments shows that the size and length of icicle as well as the space between the adjacent icicles are factors to affect ice-melting.With the shorter icicle space,the bigger icicle size and the longer icicle-length,the surface of ice layer is enlarged and then more heat is taken away by the convection and radiation,so the ice melting time will get longer.展开更多
Four successive freezing rain/heavy snowfall processes occurred in the southern part of China from 11 January to 2 February 2008 （named ＂0801 Southern Snow Disaster＂ hereafter）, during which a large-scale blocking...Four successive freezing rain/heavy snowfall processes occurred in the southern part of China from 11 January to 2 February 2008 （named ＂0801 Southern Snow Disaster＂ hereafter）, during which a large-scale blocking circulation lasted for a long time over the mid-high latitudes of the Euro-Asian continent. This severe event is featured with a broad spatial scale, strong intensity, long duration, and serious damage. During the event, the blocking situation in the mid-high latitudes maintained quasi-sationary, but weather systems in the lower latitudes were active. Abundant water vapor was supplied, and favorable weather conditions for ice storms were formed over the large areas across the southern part of China. The results in this paper demonstrate that the significant factors responsible for the abnormal atmospheric circulation and this severe event include： 1） the very active Arctic Oscillation （AO）, which helped the permanent maintenance of the planetary-scale waves; 2） the continuous transfer of negative vorticity from the upstream region around 50°E into the blocking area, which caused the blocking situation reinforced repeatedly and sustained for a long time; and 3） the active air currents south of the Tibetan Plateau, which ensured abundant moisture supply to the southern areas of China. The 0801 Southern Snow Disaster was accompanied by extremely severe icing. In this paper, the data from Cloud-Profile Radar onboard the satellite CloudSat are used to study the dynamic and microphysical features of this event. The results show that there existed a melting layer between 2 and 4 km, and ice particles could be found above this layer and in the layer near the ground surface. Surface temperature kept between -4℃ and 0℃ with relative humidity over 90%, which provided the descending supercooled waterdrops with favorable synoptic and physical conditions to form glaze and ice at the surface via freezing, deposition and/or accretion. Causes of the event might be, as a whole, traced back to the planetary-scale systems. The study on the polar vortex anomaly in this paper reveals that changes in the polar vortex in the stratosphere preceded those in the troposphere, especially in early December 2007, while the intensification of the polar vortex in the troposphere delayed dramatically until middle January and early February of 2008. This implies that changes in the polar vortex in the stratosphere may be a precursor of the ensuing severe event and a meaningful clue for extended forecasts of such a disaster.展开更多
基金supported by the National Natural Science Foundation of China(Nos.31971541 and 32201545).
文摘Extreme weather events pose an ever-greater threat to people,infrastructure,and nature.Forest ecosystems are highly sensitive to extreme cold events that can disrupt ecosystem functions,especially in montane regions.Ice storms can be particularly destructive,with rapid ice accretion causing tree branches to break,even snapping or uprooting entire trees.In March 2022,the Shennongjia forest in central China experienced severe ice storm conditions that severely damaged over 230,300ha.We utilized this opportunity to assess the vulnerability of different tree types(coniferous,deciduous,and evergreen broad-leaved)and stand compositions to damage resulting from ice glaze along an elevation gradient from 1,200 to 2,400m a.s.l.Among the 7,144 trees surveyed,10.1%suffered some extent of damage,which was most prolific in the middle elevation zone.While 96.8%of all damage occurred to deciduous broadleaved trees that dominated the forest community,the most severe damage(uprooting and lower trunk breakage)occurred to coniferous trees.The extent and severity of tree damage were moderated by forest composition,with secondary effects of forest structure and slope.Abiotic factors predominantly affected coniferous trees.We emphasize that more research and monitoring are needed to better understand the full impact of extreme weather events on forests,especially as the frequency and intensity of these events increases due to climate change.
基金supported by the Shenzhen Strategic Emerging Industrial Development Funds(GCZX20120618100801416)from Shenzhen Municipal People’s Government,China
文摘Cunninghamia lanceolata （Lamb.） Hook. is economically the most important tree species in southern China and has been cultivated in plantations on a large scale. This species is widely used in construction, furniture, utensils and shipbuilding. Soil fertility of C. lanceolata stands affects soil structure, porosity and nutrient availability, which causes changes in fauna activity. During January to February 2008, an ice storm caused extensive damage to C. lanceolata stands. Despite the environmental importance of soil fauna, basic information on the distribution and diversity of soil fauna in C. lanceolata stands after ice storm damage is lacking. To assess the response of soil fauna diversity and distribution to forest gaps following the ice storm, five small gaps （each 30-40 m^2）, five large gaps （each 80-100 m^2） and five canopy cover plots were selected within a 2-ha C. lanceolata stand. Soil samples were collected from 0 to 10 cm depth in March 2011 to measure soil fauna diversity and abundance. The abundance and community composition of the soil fauna varied with gap size. In canopy cover sites, the number of individuals was 2.0 and 5.2 times greater than in the small gaps and large gaps. Three taxa （Nematoda, Oribatida and lnsecta） of soil inver- tebrates occurred commonly, and Nematoda dominated the communities in all three habitat types. The Shannon-Wiener diversity index, Margalef diversity index, and Pielou evenness index were high in the small gaps, indicating that they harbored the most species, with the most even distribution, and the highest diversity. Our results indicated that gap size apparently affected abundance and community composition of the soil fauna.
基金supported by the National Natural Science Foundation of China(Nos.32201545,31971541).
文摘Ice storms,as important sources of frequent and injurious disturbances,drive forest dynamics in the Northern Hemisphere.However,stand-level differential vulnerability to ice storms and the associated factors that predispose forest stands remain unclear.This is particularly concerning in the subtropics where the frequency of ice storms is predicted to increase with global warming.Here we assessed how the impact on three forest stands(early and late secondary-growth forests,and old-growth forests)differed after an extreme ice storm during 20–21 March 2022,and identified the abiotic and biotic factors that determine the damage intensity in the Shennongjia World Natural Heritage Site,a biodiversity conservation hotspot in central China.We found a stand-specific‘middomain effect’where the late secondary-growth forest sustained the most severe damage,the early secondarygrowth forest sustained the least,and the old-growth forest suffered an intermediate amount.‘Crown broken’was the most severe damage type across all three forest stands,although the proportion of‘branch broken’was also high in the old-growth forest.Topography played a significant role in determining the vulnerability of the early secondary-growth forest to severe ice storms whereas the forest structure and composition were important factors in explaining the damage rates in the old-growth forest,although they differed among the damage categories.In contrast,topography,forest structure and composition generally explain the intensity of damage in the late secondary-growth forests.Our results highlight that,in subtropical forests,the intensity of damage caused by severe ice storms and related determining factors are stand-level dependent.We also suggest exploring potential management strategies(e.g.,slow-growing hardwood species that can resist storms should be the main species for reforestation in early secondary-growth forests)to mitigate the risk of future severe ice storms,as well as other wind-related climatic extremes.
基金supported by the Croatian Science Foundation(project number IP-2018-01-8820)the Slovenian Research Agency core funding(grant number P4-0059).
文摘Ice storms can cause substantial damage to tree crowns and lead to growth reduction.However,in uneven-aged stands,the growth of an individual tree may also increase due to crown release caused by the damage or mortality of neighboring trees.Three years after the devastating ice storm in 2014 in mixed uneven-aged Dinaric forests(Croatia),we cored 156 European beech(Fagus sylvatica)and 85 silver fir(Abies alba)trees across 20 permanent sample plots to study the post-storm growth response as a function of tree,stand,site,spatial arrangement and local competition factors.The ice storm damaged over 84% of trees on the sampled plots.Among the cored trees,52.7% exhibited growth reduction,which on average amounted to3.1%relative to the pre-disturbance average.Trees with less than 40% crown damage maintained their pre-disturbance growth rates or experienced only minor growth suppression.While 60% of beech trees suffered a growth reduction at an average rate of 7.2%,the average radial increment of fir after the storm was 14.0% higher compared to the pre-storm rate.A linear mixedeffects model suggests that the growth response can largely be explained by the focal and neighboring tree species identity,tree competition pressure,focal and neighboring tree damage,crown size,slenderness index and stoniness.Growth release was positively associated with fir,inverse distance-weighted crown damage of the nearest neighbor,shorter crowns,slenderness,less stony sites and less damaged trees.The analysis suggests that at the same level of local competition load,trees with a broadleaved and damaged nearest neighbor are more likely to experience growth release than those with a coniferous or undamaged nearest neighbor.This implies that unevenaged stands with a substantial presence and mingling of both conifers and broadleaves are expected to be more resilient to ice storms and are less likely to suffer growth reduction.
基金This research was funded by the National Natural Science Foundation of China(Grant number 32071683)the Project of Fundamental Research Funds for the Central Universities(2662023YLPY003).
文摘Assessing forest loss from snow and ice storms is vital for disaster evaluation and sustainable management.Traditional optical remote sensing methods,which focus on horizontal canopy changes,struggle to capture vertical stand alterations caused by snow and ice storms.This study introduces the LiDAR Forest Structure Change Index(LFSCI),a novel index that employs bitemporal unmanned aerial vehicle(UAV)LiDAR point data to comprehensively evaluate changes in the vertical distribution of forest stands.Following ice storms in Shi-zishan,Wuhan,China in early 2024,research was conducted to compare the performance of LFSCI with tradi-tional metrics,such as canopy cover(CC),Leaf Area Index(LAI),and tree height(TH),across two spatial scales(grid and individual tree).LFSCI was evaluated at nine point densities(5-177 pt/m^(2)).Through validation with field-measured stand volume changes from 43 plots,LFSCI showed superior correlation(R^(2)=0.64 for grids,0.59 for trees)in comparison to CC(R^(2)=0.52),LAI(R^(2)=0.38),and TH(R^(2)=0.16).Higher point densities enhanced accuracy,with 50 pt/m^(2) recommended for effective snow and ice storm impact detection.Pure broad-leaved forests were more susceptible to loss in comparison to mixed conifer-broadleaf forests,mixed broadleaf for-ests,and needle forests.Additionally,stands characterized by greater tree heights,steeper slopes,and shaded conditions were more vulnerable to damage than those in other environments.
文摘This paper proposes a co-optimal strategy using line hardening,mobile devices(mobile ice-melting device,mobile emergency generator,mobile energy storage system),and repair crew dispatching to improve distribution system resilience during ice storms.A multi-stage defender-attacker-defender model is established to take into account interactions and coupling relationships between different measures.In our proposed model,ice storms will attack the distribution and transportation system in a worst-case scenario,affecting system performance from various perspectives.Corresponding to the different operating states in the distribution system affected by ice storms,aiming at minimizing the weighted load shedding value,this paper applies various measures to different stages to improve the response and defense capabilities to ice storms and realize restoration of the distribution system ultimately.The nested column-and-constraint generation algorithm is used to solve the model efficiently.The effectiveness of the proposed model and solution method for enhancing the distribution system resilience is verified on the modified IEEE 33-bus distribution system and modified realworld zone of Caracas 141-bus distribution system.
基金the National Natural Science Foundation of China(31672265,31670445)the GDAS Special Project of Science and Technology Development(2018GDASCX-0107)+1 种基金the First Wildlife Monitoring of National Forest Nature Reserve in Guangdong(0877-16GZTP01D060)the Forest Resource Survey and Cultivation of Chebaling National Nature Reserve(SX15GZ022)to F.S.Zou.
文摘Between January and February 2008,a severe ice storm occurred in southern China.The storm damaged nearly 21 million hectares of forest lands with broken branch,trunk breakage,and stem bending of many trees.This natural disturbance provides a unique opportunity to study impacts of extreme climatic event on forest birds.Using hierarchical multi-species occupancy model(species richness;27 species)and N-mixture model(abundance;3 species),we investigated how the storm affected resident bird species in subtropical forest in southern China.We sampled birds at Chebaling National Nature Reserve in Guangdong Province,monthly for 1 year each before and after the storm by mist nets.To take into account variations in temperature between years and between months,we incorporated monthly mean temperature into the models as an additional covariate.Observed species richness was greater before the storm.Estimated species richness(from the hierarchical model)also tended to be greater before than after the storm although 95%Bayesian credible intervals of these estimates were overlapped.Temperature showed a negative effect on estimated species richness,indicating greater species richness during winter.Among three species captured the most,abundance of Chestnut Bulbul(Hemixos castanonotus)significantly decreased after the storm.Other two species,Grey Treepie(Dendrocitta formosae)and Huet’s Fulvetta(Alcippe hueti)showed insignificant responses to the storm.Our study indicates that the 2008 ice storm may not have a significant impact on species richness of resident birds in subtropical forest;however,the effect can be species-specific and negative to some species’population.
基金supported by the Special Funds for Major State Basic Research Projects of China(973 Program)(Grant No.2009CB724501)the Natural Science Foundation Project of CQ CSTC(2008BB6157)
文摘Icicles are often formed under the downside surface of conductor in the wet growth icing of overhead power line.When the ice deposit around overhead power line is molten by Joule heat produced by current,the pattern of heat transfer of ice deposit with icicles is dissimilar to that without icicle,so the ice-melting model for the columnar icing conductor cannot be applied to icicle-shaped icing conductor.According to the heat-transfer characteristic of the icicle-shaped icing conductor,this paper puts forward a DC ice-melting model for the icicle-shaped icing conductor.Because this full model includes three-dimensional heat-transfer and interface movement,which cannot be solved in closed form,a finite element scheme in space-domain and a finite difference scheme in time-domain are employed to discretize the governing equations.Firstly the whole ice-melting process on the icicle-shaped icing conductor is simulated by this model.Then the simulated results are validated by ice-melting experiments in the artificial chamber.The study from the model and the experiments shows that the size and length of icicle as well as the space between the adjacent icicles are factors to affect ice-melting.With the shorter icicle space,the bigger icicle size and the longer icicle-length,the surface of ice layer is enlarged and then more heat is taken away by the convection and radiation,so the ice melting time will get longer.
基金Supported jointly by the Basic Research Project of the State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciencesthe National Natural Science Foundation of China under Grant Nos. 40633016 and 40875029
文摘Four successive freezing rain/heavy snowfall processes occurred in the southern part of China from 11 January to 2 February 2008 （named ＂0801 Southern Snow Disaster＂ hereafter）, during which a large-scale blocking circulation lasted for a long time over the mid-high latitudes of the Euro-Asian continent. This severe event is featured with a broad spatial scale, strong intensity, long duration, and serious damage. During the event, the blocking situation in the mid-high latitudes maintained quasi-sationary, but weather systems in the lower latitudes were active. Abundant water vapor was supplied, and favorable weather conditions for ice storms were formed over the large areas across the southern part of China. The results in this paper demonstrate that the significant factors responsible for the abnormal atmospheric circulation and this severe event include： 1） the very active Arctic Oscillation （AO）, which helped the permanent maintenance of the planetary-scale waves; 2） the continuous transfer of negative vorticity from the upstream region around 50°E into the blocking area, which caused the blocking situation reinforced repeatedly and sustained for a long time; and 3） the active air currents south of the Tibetan Plateau, which ensured abundant moisture supply to the southern areas of China. The 0801 Southern Snow Disaster was accompanied by extremely severe icing. In this paper, the data from Cloud-Profile Radar onboard the satellite CloudSat are used to study the dynamic and microphysical features of this event. The results show that there existed a melting layer between 2 and 4 km, and ice particles could be found above this layer and in the layer near the ground surface. Surface temperature kept between -4℃ and 0℃ with relative humidity over 90%, which provided the descending supercooled waterdrops with favorable synoptic and physical conditions to form glaze and ice at the surface via freezing, deposition and/or accretion. Causes of the event might be, as a whole, traced back to the planetary-scale systems. The study on the polar vortex anomaly in this paper reveals that changes in the polar vortex in the stratosphere preceded those in the troposphere, especially in early December 2007, while the intensification of the polar vortex in the troposphere delayed dramatically until middle January and early February of 2008. This implies that changes in the polar vortex in the stratosphere may be a precursor of the ensuing severe event and a meaningful clue for extended forecasts of such a disaster.
