Based on the conventional observation data,daily reanalysis data from NCAR/NCEP,and TBB data derived from FY-2G infrared cloud images in April 2018,a heavy snowfall weather process in central Inner Mongolia from April...Based on the conventional observation data,daily reanalysis data from NCAR/NCEP,and TBB data derived from FY-2G infrared cloud images in April 2018,a heavy snowfall weather process in central Inner Mongolia from April 4 to 6 in 2018 was analyzed.The results show that the low trough at 500 hPa,the southerly wind jet stream at 700 hPa,and the inverted trough on the ground were the main influencing systems causing this blizzard.The transportation of warm and humid air by the southerly wind jet stream at 700 hPa and intense water vapor convergence provided sufficient water vapor conditions for the blizzard,and the moist layer in the blizzard area was deep.The low-level MPV in the blizzard area was<0,and the atmosphere was in a conditional symmetric instability state.The coupling of the upper and lower-level jets induced strong ascending motion.With the invasion of cold air,a low-level cold pad was formed,so that the warm and humid air tilted upward.The secondary circulation updraft triggered by the wet Q vector system released the conditional symmetric instability energy,so that the sloping motion was more intense,and the heavy snowfall appeared.Meanwhile,there was a good correspondence relationship between the blizzard area and the large-value area of low-level wet Q vector divergence.The mesoscale cloud clusters continuously generating,merging,and moving eastward in Hetao area were the direct cause of this blizzard,and the TBB of the cloud clusters was≤-56℃.The blizzard happened in the the edge gradient and large-value area of TBB.展开更多
Typhoon Meranti originated over the western North Pacific off the south tip of the Taiwan Island in 2010.It moved westward entering the South China Sea,then abruptly turned north into the Taiwan Strait,got intensified...Typhoon Meranti originated over the western North Pacific off the south tip of the Taiwan Island in 2010.It moved westward entering the South China Sea,then abruptly turned north into the Taiwan Strait,got intensified on its way northward,and eventually made landfall on Fujian province.In its evolution,there was a northwest-moving cold vortex in upper troposphere to the south of the Subtropical High over the western North Pacific(hereafter referred to as the Subtropical High).In this paper,the possible impacts of this cold vortex on Meranti in terms of its track and intensity variation is investigated using typhoon best track data from China Meteorological Administration,analyses data of 0.5×0.5 degree provided by the global forecasting system of National Centers for Environmental Prediction,GMS satellite imagery and Taiwan radar data.Results show as follows:(1)The upper-level cold vortex was revolving around the typhoon anticlockwise from its east to its north.In the early stage,due to the blocking of the cold vortex,the role of the Subtropical High to steer Meranti was weakened,which results in the looping of the west-moving typhoon.However,when Meranti was coupled with the cold vortex in meridional direction,the northerly wind changed to the southerly at the upper level of the typhoon;at the same time the Subtropical High protruded westward and its southbound steering flow gained strength,and eventually created an environment in which the southerly winds in both upper and lower troposphere suddenly steered Meranti to the north;(2)The change of airflow direction above the typhoon led to a weak vertical wind shear,which in return facilitated the development of Meranti.Meanwhile,to the east of typhoon Meranti,the overlapped southwesterly jets in upper and lower atmosphere accelerated its tangential wind and contributed to its cyclonic development;(3)The cold vortex not only supplied positive vorticity to the typhoon,but also transported cold advection to its outer bands.In conjunction with the warm and moist air masses at the lower levels,the cold vortex increased the vertical instability in the atmosphere,which was favorable for convection development within the typhoon circulation,and its warmer center was enhanced through latent heat release;(4)Vertical vorticity budget averaged over the typhoon area further shows that the intensification of a typhoon vorticity column mainly depends on horizontal advection of its high-level vorticity,low-level convergence,uneven wind field distribution and its convective activities.展开更多
A statistically-based low-level cloud parameterization scheme is introduced, modified, and applied in the Flexible coupled General Circulation Model (FGCM-O). It is found that the low-level cloud scheme makes improved...A statistically-based low-level cloud parameterization scheme is introduced, modified, and applied in the Flexible coupled General Circulation Model (FGCM-O). It is found that the low-level cloud scheme makes improved simulations of low-level cloud fractions and net surface shortwave radiation fluxes in the subtropical eastern oceans off western coasts in the model. Accompanying the improvement in the net surface shortwave radiation fluxes, the simulated distribution of SSTs is more reasonably asymmetrical about the equator in the tropical eastern Pacific, which suppresses, to some extent, the development of the double ITCZ in the model. Warm SST biases in the ITCZ north of the equator are more realistically reduced, too. But the equatorial cold tongue is strengthened and extends further westward, which reduces the precipitation rate in the western equatorial Pacific but increases it in the ITCZ north of the equator in the far eastern Pacific. It is demonstrated that the low-level cloud-radiation feedback would enhance the cooperative feedback between the equatorial cold tongue and the ITCZ. Based on surface layer heat budget analyses, it is demonstrated that the reduction of SSTs is attributed to both the thermodynamic cooling process modified by the increase of cloud fractions and the oceanic dynamical cooling processes associated with the strengthened surface wind in the eastern equatorial Pacific, but it is mainly attributed to oceanic dynamical cooling processes associated with the strengthening of surface wind in the central and western equatorial Pacific.展开更多
The snow enhancement experiments, carried out by injecting AgI and water vapor into orographically enhanced clouds （fog）, have been conducted to confirm Li and Pitter＇s forced condensation process in a natural situ...The snow enhancement experiments, carried out by injecting AgI and water vapor into orographically enhanced clouds （fog）, have been conducted to confirm Li and Pitter＇s forced condensation process in a natural situation. Nine ground-based experiments have been conducted at Daegwallyeong in the Taebaek Mountains for the easterly foggy days from January-February 2006. We then obtained the optimized conditions for the Daegwallyeong region as follows： the small seeding rate （1.04 g min-1） of AgI for the easterly cold fog with the high humidity of Gangneung. Additional experiments are needed to statistically estimate the snowfall increment caused by the small AgI seeding into the orographical fog （cloud） over the Taeback Mountains.展开更多
The microphysical characteristics of wintertime cold clouds in North China were investigated from 22 aircraft observation flights from 2014 to 2017,2020,and 2021.The clouds were generated by mesoscale weather systems ...The microphysical characteristics of wintertime cold clouds in North China were investigated from 22 aircraft observation flights from 2014 to 2017,2020,and 2021.The clouds were generated by mesoscale weather systems with little orographic component.Over the mixed-phase temperature range(–40℃to 0℃),the average fraction of liquid,mixedphase,and ice cloud was 4.9%,23.3%,and 71.8%,respectively,and the probability distribution of ice mass fraction was a half-U-shape,suggesting that ice cloud was the primary cloud type.The wintertime mixed-phase clouds in North China were characterized by large cloud droplet number concentration,small liquid water content(LWC),and small effective diameter of cloud droplets.The main reason for larger cloud droplet number concentration and smaller effective diameter of cloud droplets was the heavy pollution in winter in North China,while for smaller LWC was the lower temperature during flights and the difference in air mass type.With the temperature increasing,cloud droplet number concentration,LWC,and the size of ice particles increased,but ice number concentration and effective diameter of cloud droplets decreased,similar to other mid-latitude regions,indicating the similarity in the temperature dependence of cloud properties of mixed-phase clouds.The variation of the cloud properties and ice habit at different temperatures indicated the operation of the aggregation and riming processes,which were commonly present in the wintertime mixed-phase clouds.This study fills a gap in the aircraft observation of wintertime cold clouds in North China.展开更多
On the night of April 20, 2017, there was a heavy rain in Longyan City, accompanied by strong convective weather such as strong lightning, short-term heavy precipitation, and 6 - 8 thunderstorms. The three-hour rain i...On the night of April 20, 2017, there was a heavy rain in Longyan City, accompanied by strong convective weather such as strong lightning, short-term heavy precipitation, and 6 - 8 thunderstorms. The three-hour rain intensity and the six-hour rain intensity of Shanghang Tongxian Township and Nanyang Town were once in a century. Through the use of radar, radar wind profile and lightning locator data, the process can be divided into two phases: The first stage is the strong precipitation stage of Changting Datong Town during the 20 - 22 periods on the 20th. The process is accompanied by short-term heavy precipitation (59.7 mm/h), strong lightning activity, and 6 - 8 thunderstorm gales. It is a convective cold cloud dominated precipitation. The second stage is the strong precipitation stage of Shanghang Tongxian Township on the 21st, 02 - 04, and the short-term strong precipitation intensity reaches 75.7 mm/h, but the lightning and wind activity are weak, which is the convective warm cloud-oriented precipitation. There are significant differences in the strong convective weather between the two phases in the same background. The analysis shows that the strong echo of the first stage radar (above 60 dBz) is block-shaped southward, the speed of movement is fast, the height of the echo top is high, and the rear nascent monomer forms a train effect. In the second stage, the southwest-northeast-oriented convective zone moves to the northeast direction, forming the train effect of the echo zone. The center intensity is above 50 dBz, the echo top height is low, and the precipitation center moves slowly. This caused a large amount of accumulated rainfall. In this paper, the radar data is used to analyze the heavy rainfall process on the west coast of the straits, which has certain indication significance for the predictability of strong convective weather.展开更多
[Objective] The aim was to summarize the characteristics of refelectivity factors of Doppler radar of the cold front cloud system. [Method] Judging from the characteristics of reflectivity factors, by dint of the new ...[Objective] The aim was to summarize the characteristics of refelectivity factors of Doppler radar of the cold front cloud system. [Method] Judging from the characteristics of reflectivity factors, by dint of the new generation weather radar in Harbin from 2002 to 2007, the features of the reflectivity factors of the cold front cloud system were summarized. [Result] The cloud formed by the cold front was in banded form in general. However, there was void in the cloud and its intensity was uneven. Most fast moving cold front was long and narrow banded echo and basically the radial velocity turned from northwest wind to southwest. With the changes of month, the feature of the reflective rate also changed. In winter, the cold front cloud was in layer form. The feature of the reflectivity factors was weak and in large area. However, the structure was loose and there was space in the echo. Among them, there were several strong echoes. Strong convection cell echo formed in the two sides of the cold front, and it moved with the entire cloud belt. When the dry cold front moved, regional strong convective current formed, mainly by convective cloud and small echo area. Generally, the changes of the wind direction can not be expounded from the radial velocity. However, the intensity of the convection cell was distinct, 'three-body scattering', 'side lobe echo', and 'weak echo', as well as features of super convection cell. [Conclusion] The study provided positive role for the application of Doppler radar in the surveillance of weather in Heilongjiang Province.展开更多
We present a cold atom system with a dark-line two-dimensional magneto-optical trap, to increase the atomic density by suppressing the atomic radiation pressure. Optical depth （OD） and duty cycle are used to evaluat...We present a cold atom system with a dark-line two-dimensional magneto-optical trap, to increase the atomic density by suppressing the atomic radiation pressure. Optical depth （OD） and duty cycle are used to evaluate the system performance. We demonstrate a 100% increase in OD with the dark line, and obtain an ultrahigh OD of 264 with 10% for the duty cycle. Also, with an efficient dark line region, the OD could maintain above i00 with duty cycle as high as 30%. The cold atomic ensemble with an ultrahigh OD with a 10%-30% duty cycle is particularly advantageous in quantum i^formation processing and communication.展开更多
晴空颠簸是影响飞机安全运行和旅客旅行舒适度的重要恶劣天气之一。为了研究2017年6月6日02:10(协调世界时)发生在山西省长治市上空的一次强烈的晴空颠簸事件的产生机制,本文使用常规观测资料、NOAA-15和NOAA-18卫星辐射资料并通过天气...晴空颠簸是影响飞机安全运行和旅客旅行舒适度的重要恶劣天气之一。为了研究2017年6月6日02:10(协调世界时)发生在山西省长治市上空的一次强烈的晴空颠簸事件的产生机制,本文使用常规观测资料、NOAA-15和NOAA-18卫星辐射资料并通过天气学分析和中尺度WRF数值模式以及GSI(Grid point Statistical Interpolation)同化系统同化等方法,对此次事件开展了数值模拟和机理研究。结果表明:该次飞机颠簸事件是一个典型的高空急流—锋区耦合系统导致的晴空湍流所致,高空急流是导致晴空湍流的主要因素之一。导致该次晴空湍流事件发生的是大气一系列要素对冷空气入侵的响应。高空冷云(冷空气)发展南下是促进此次强颠簸事件发生的重要诱因。由于高空冷云的南下,使得长治上空温度经向梯度增加,而长治上空温度经向梯度增加,使得中纬度风切变增大,增大的水平风垂直切变,导致理查森数(Ri)数值变小,而较小的Ri值是产生KH(Kelvin-Helmholtz)不稳定的必要条件,由于K-H不稳定导致了长治上空出现晴空湍流。此外,中尺度WRF模式以及GSI同化系统能够较好地模拟颠簸区附近的大气温度场特征,表明文中的数值预报流程对于大气温度、风场以及晴空湍流的发展具有一定的预报能力。展开更多
In this study, an east-moving Tibetan Plateau vortex(TPV) is analyzed by using the ERA-5 reanalysis and multi-source satellite data, including FengYun-2 E, Aqua/MODIS and CALIPSO. The objective is to demonstrate:(i) t...In this study, an east-moving Tibetan Plateau vortex(TPV) is analyzed by using the ERA-5 reanalysis and multi-source satellite data, including FengYun-2 E, Aqua/MODIS and CALIPSO. The objective is to demonstrate:(i) the usefulness of multi-spectral satellite observations in understanding the evolution of a TPV and the associated rainfall, and(ii) the potential significance of cloud-top quantitative information in improving Southwest China weather forecasts. Results in this study show that the heavy rainfall is caused by the coupling of an east-moving TPV and some low-level weather systems [a Plateau shear line and a Southwest Vortex(SWV)], wherein the TPV is a key component. During the TPV's life cycle, the rainfall and vortex intensity maintain a significant positive correlation with the convective cloud-top fraction and height within a 2.5?radius away from its center. Moreover, its growth is found to be quite sensitive to the cloud phases and particle sizes. In the mature stage when the TPV is coupled with an SWV, an increase of small ice crystal particles and appearance of ring-and U/V-shaped cold cloud-top structures can be seen as the signature of a stronger convection and rainfall enhancement within the TPV. A tropopause folding caused by ageostrophic flows at the upper level may be a key factor in the formation of ring-shaped and U/V-shaped cloud-top structures. Based on these results, we believe that the supplementary quantitative information of an east-moving TPV cloud top collected by multi-spectral satellite observations could help to improve Southwest China short-range/nowcasting weather forecasts.展开更多
The characteristics of summertime raindrop size distribution(DSD) and associated relations in the semi-arid region over the Inner Mongolian Plateau(IMP) were investigated,utilizing five-year continuous observations by...The characteristics of summertime raindrop size distribution(DSD) and associated relations in the semi-arid region over the Inner Mongolian Plateau(IMP) were investigated,utilizing five-year continuous observations by a PARSIVEL2disdrometer in East Ujimqin County(EUC),China.It is found that only 7.94% of the 15 664 one-min precipitation samples meet classification criteria as convective rain(CR),but its contribution to the total rainfall amount is 63.87%.Notably,40.72% of the rainfall comes from large-sized raindrops(D> 3 mm),despite the fact that large-sized raindrops account for only 1.73% of the CR total number concentration.Further results show that the mean value of mass-weighted mean diameters(Dm) is larger(2.43 mm) and generalized intercepts(lgN_(W)) is lower(3.19) in CR,aligning with a "continentallike" cluster,which is mainly influenced by the joint impact of in-cloud ice-based processes and the below-cloud environmental background.Also,the empirical relationships of shape-slope(μ-Λ),radar reflectivity-rain rate(Z-R),and rainfall kinetic energy(KE_(time)-Rand KE_(time)-Z) are localized.To quantitatively analyze the impact of DSD parameters on kinetic energy estimation,power-law KE_(time)-R and KE_(time)-Z relationships are derived based on the normalized gamma distribution.N_(W)takes precedence over μ in affecting variabilities of multiplicative coefficients,especially for KE_(time)-R relationship where the multiplicative coefficient is proportional to N_(W)^(-0.287).It should be noted that although the proportion of CR occurring throughout the summer is small,raindrops with lower N_(W) and larger Dmwill generate higher KE_(time),which will bring a higher potential risk of soil erosion in semi-arid regions over IMP.展开更多
对小云粒子(粒径<50μm)的相态进行检测是云物理飞机测量领域的一个难点,而利用云粒子的偏振信息对云粒子相态进行鉴别是目前云物理研究领域比较认可的一种方法。本文针对偏振云粒子谱仪(cloud aerosol spectrometer with depolariza...对小云粒子(粒径<50μm)的相态进行检测是云物理飞机测量领域的一个难点,而利用云粒子的偏振信息对云粒子相态进行鉴别是目前云物理研究领域比较认可的一种方法。本文针对偏振云粒子谱仪(cloud aerosol spectrometer with depolarization,CAS-DPOL)所测云粒子偏振参量的应用需求展开研究,通过对现有方法的比较分析,整合出一套适合于该仪器的方法和阈值。基于所整合出的方法和阈值以及该仪器在2021年5月23日东北冷涡天气的一次航测结果,探讨了该仪器在人工影响天气和飞机自然结冰探测领域的应用,此次航测发现温度在-1~-8℃的云内过冷云滴数对总云粒子数占比的平均值可达到80.18%,云相以混合相为主,间有纯过冷水云相存在;此次航测以云粒子谱仪所测数浓度大于5 cm^(-3)作为过冷滴存在的下限判定指标是比较可信的;此外,飞机在此次航测中的自然结冰强度为微量结冰,没有探测到符合《运输类飞机适航标准》附录C曲线要求的结冰气象条件。展开更多
对流云是南方人工增雨开发利用空中云水资源的重要对象,结构复杂多变;通过数值模式合理评估催化作业过程,进而研究其催化机制,是建立和改进催化作业技术的必要途径,也是评估实际人工增雨作业效果的有效手段。利用耦合了碘化银(AgI)催化...对流云是南方人工增雨开发利用空中云水资源的重要对象,结构复杂多变;通过数值模式合理评估催化作业过程,进而研究其催化机制,是建立和改进催化作业技术的必要途径,也是评估实际人工增雨作业效果的有效手段。利用耦合了碘化银(AgI)催化的WRF(Weather Research and Forecasting)模式,对2021年5月4日福建古田人工增雨随机化试验个例开展催化模拟,分析AgI核化机制、催化对云系宏微观特征、降水机制的影响以及增雨效果评估。结果显示,AgI播撒后呈带状扩散,催化前期(09:00—11:00)(世界时,下同)地面降水增量缓慢增加;随后(11:00—13:00)降水增幅加大并出现剧烈波动;13:00后降水增量以负值为主。AgI主要核化机制为凝华核化,核化持续约40 min。AgI播撒后主要通过凝华核化使冰晶数浓度大幅增加(增量约3~9个·L^(-1)),增长的冰晶大部分转化为雪晶,再通过雪晶融化增加云中雨滴质量浓度。此次过程催化影响时间持续约4 h,催化部位绝对增雨量约-0.78~1.24 mm,增雨率约-8.3%~12.1%,总降水增量为4.64×10^(5) t,增雨效果显著。展开更多
基金Supported by the Meteorological Science and Technology Innovation Project of North China(HBXM202415)Research Project of the Meteorological Bureau of Inner Mongolia Autonomous Region(nmqxkjcx202311).
文摘Based on the conventional observation data,daily reanalysis data from NCAR/NCEP,and TBB data derived from FY-2G infrared cloud images in April 2018,a heavy snowfall weather process in central Inner Mongolia from April 4 to 6 in 2018 was analyzed.The results show that the low trough at 500 hPa,the southerly wind jet stream at 700 hPa,and the inverted trough on the ground were the main influencing systems causing this blizzard.The transportation of warm and humid air by the southerly wind jet stream at 700 hPa and intense water vapor convergence provided sufficient water vapor conditions for the blizzard,and the moist layer in the blizzard area was deep.The low-level MPV in the blizzard area was<0,and the atmosphere was in a conditional symmetric instability state.The coupling of the upper and lower-level jets induced strong ascending motion.With the invasion of cold air,a low-level cold pad was formed,so that the warm and humid air tilted upward.The secondary circulation updraft triggered by the wet Q vector system released the conditional symmetric instability energy,so that the sloping motion was more intense,and the heavy snowfall appeared.Meanwhile,there was a good correspondence relationship between the blizzard area and the large-value area of low-level wet Q vector divergence.The mesoscale cloud clusters continuously generating,merging,and moving eastward in Hetao area were the direct cause of this blizzard,and the TBB of the cloud clusters was≤-56℃.The blizzard happened in the the edge gradient and large-value area of TBB.
基金Natural Fundamental Research and Development Project"973"Program(2009CB421504)Natural Science Foundation of China(40975032+2 种基金4073094841075037)Special Project of Chinese Academy of Meteorological Sciences(2007Y006)
文摘Typhoon Meranti originated over the western North Pacific off the south tip of the Taiwan Island in 2010.It moved westward entering the South China Sea,then abruptly turned north into the Taiwan Strait,got intensified on its way northward,and eventually made landfall on Fujian province.In its evolution,there was a northwest-moving cold vortex in upper troposphere to the south of the Subtropical High over the western North Pacific(hereafter referred to as the Subtropical High).In this paper,the possible impacts of this cold vortex on Meranti in terms of its track and intensity variation is investigated using typhoon best track data from China Meteorological Administration,analyses data of 0.5×0.5 degree provided by the global forecasting system of National Centers for Environmental Prediction,GMS satellite imagery and Taiwan radar data.Results show as follows:(1)The upper-level cold vortex was revolving around the typhoon anticlockwise from its east to its north.In the early stage,due to the blocking of the cold vortex,the role of the Subtropical High to steer Meranti was weakened,which results in the looping of the west-moving typhoon.However,when Meranti was coupled with the cold vortex in meridional direction,the northerly wind changed to the southerly at the upper level of the typhoon;at the same time the Subtropical High protruded westward and its southbound steering flow gained strength,and eventually created an environment in which the southerly winds in both upper and lower troposphere suddenly steered Meranti to the north;(2)The change of airflow direction above the typhoon led to a weak vertical wind shear,which in return facilitated the development of Meranti.Meanwhile,to the east of typhoon Meranti,the overlapped southwesterly jets in upper and lower atmosphere accelerated its tangential wind and contributed to its cyclonic development;(3)The cold vortex not only supplied positive vorticity to the typhoon,but also transported cold advection to its outer bands.In conjunction with the warm and moist air masses at the lower levels,the cold vortex increased the vertical instability in the atmosphere,which was favorable for convection development within the typhoon circulation,and its warmer center was enhanced through latent heat release;(4)Vertical vorticity budget averaged over the typhoon area further shows that the intensification of a typhoon vorticity column mainly depends on horizontal advection of its high-level vorticity,low-level convergence,uneven wind field distribution and its convective activities.
基金This study was jointly supported by the National Science Foundation of China under Grant No.s40233031 and 40221503the National Key Basic Research Project under Grant No.G200078502.
文摘A statistically-based low-level cloud parameterization scheme is introduced, modified, and applied in the Flexible coupled General Circulation Model (FGCM-O). It is found that the low-level cloud scheme makes improved simulations of low-level cloud fractions and net surface shortwave radiation fluxes in the subtropical eastern oceans off western coasts in the model. Accompanying the improvement in the net surface shortwave radiation fluxes, the simulated distribution of SSTs is more reasonably asymmetrical about the equator in the tropical eastern Pacific, which suppresses, to some extent, the development of the double ITCZ in the model. Warm SST biases in the ITCZ north of the equator are more realistically reduced, too. But the equatorial cold tongue is strengthened and extends further westward, which reduces the precipitation rate in the western equatorial Pacific but increases it in the ITCZ north of the equator in the far eastern Pacific. It is demonstrated that the low-level cloud-radiation feedback would enhance the cooperative feedback between the equatorial cold tongue and the ITCZ. Based on surface layer heat budget analyses, it is demonstrated that the reduction of SSTs is attributed to both the thermodynamic cooling process modified by the increase of cloud fractions and the oceanic dynamical cooling processes associated with the strengthened surface wind in the eastern equatorial Pacific, but it is mainly attributed to oceanic dynamical cooling processes associated with the strengthening of surface wind in the central and western equatorial Pacific.
基金supported by the Korea Science and Engineering Foundation (KOSEF)grant funded by the Korea government (MOST) R01-2006-000-10470-0 and R01-2006-000-11233-0 from the Basic Research Program of the Korea Science & Engineering Foundationby "Maintenance and Research of Cloud Phys-ical Observation System" and "Research for the Meteo-rological Observation Technology and its Application" ofMETRI, KMA project.
文摘The snow enhancement experiments, carried out by injecting AgI and water vapor into orographically enhanced clouds （fog）, have been conducted to confirm Li and Pitter＇s forced condensation process in a natural situation. Nine ground-based experiments have been conducted at Daegwallyeong in the Taebaek Mountains for the easterly foggy days from January-February 2006. We then obtained the optimized conditions for the Daegwallyeong region as follows： the small seeding rate （1.04 g min-1） of AgI for the easterly cold fog with the high humidity of Gangneung. Additional experiments are needed to statistically estimate the snowfall increment caused by the small AgI seeding into the orographical fog （cloud） over the Taeback Mountains.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41925023, 91744208, 41575073, 41621005, and 42075084)by the Ministry of Science and Technology of the People’s Republic of China (Grant Nos. 2017YFA0604002 and 2016YFC0200503)supported by the Collaborative Innovation Center of Climate Change, Jiangsu Province
文摘The microphysical characteristics of wintertime cold clouds in North China were investigated from 22 aircraft observation flights from 2014 to 2017,2020,and 2021.The clouds were generated by mesoscale weather systems with little orographic component.Over the mixed-phase temperature range(–40℃to 0℃),the average fraction of liquid,mixedphase,and ice cloud was 4.9%,23.3%,and 71.8%,respectively,and the probability distribution of ice mass fraction was a half-U-shape,suggesting that ice cloud was the primary cloud type.The wintertime mixed-phase clouds in North China were characterized by large cloud droplet number concentration,small liquid water content(LWC),and small effective diameter of cloud droplets.The main reason for larger cloud droplet number concentration and smaller effective diameter of cloud droplets was the heavy pollution in winter in North China,while for smaller LWC was the lower temperature during flights and the difference in air mass type.With the temperature increasing,cloud droplet number concentration,LWC,and the size of ice particles increased,but ice number concentration and effective diameter of cloud droplets decreased,similar to other mid-latitude regions,indicating the similarity in the temperature dependence of cloud properties of mixed-phase clouds.The variation of the cloud properties and ice habit at different temperatures indicated the operation of the aggregation and riming processes,which were commonly present in the wintertime mixed-phase clouds.This study fills a gap in the aircraft observation of wintertime cold clouds in North China.
文摘On the night of April 20, 2017, there was a heavy rain in Longyan City, accompanied by strong convective weather such as strong lightning, short-term heavy precipitation, and 6 - 8 thunderstorms. The three-hour rain intensity and the six-hour rain intensity of Shanghang Tongxian Township and Nanyang Town were once in a century. Through the use of radar, radar wind profile and lightning locator data, the process can be divided into two phases: The first stage is the strong precipitation stage of Changting Datong Town during the 20 - 22 periods on the 20th. The process is accompanied by short-term heavy precipitation (59.7 mm/h), strong lightning activity, and 6 - 8 thunderstorm gales. It is a convective cold cloud dominated precipitation. The second stage is the strong precipitation stage of Shanghang Tongxian Township on the 21st, 02 - 04, and the short-term strong precipitation intensity reaches 75.7 mm/h, but the lightning and wind activity are weak, which is the convective warm cloud-oriented precipitation. There are significant differences in the strong convective weather between the two phases in the same background. The analysis shows that the strong echo of the first stage radar (above 60 dBz) is block-shaped southward, the speed of movement is fast, the height of the echo top is high, and the rear nascent monomer forms a train effect. In the second stage, the southwest-northeast-oriented convective zone moves to the northeast direction, forming the train effect of the echo zone. The center intensity is above 50 dBz, the echo top height is low, and the precipitation center moves slowly. This caused a large amount of accumulated rainfall. In this paper, the radar data is used to analyze the heavy rainfall process on the west coast of the straits, which has certain indication significance for the predictability of strong convective weather.
文摘[Objective] The aim was to summarize the characteristics of refelectivity factors of Doppler radar of the cold front cloud system. [Method] Judging from the characteristics of reflectivity factors, by dint of the new generation weather radar in Harbin from 2002 to 2007, the features of the reflectivity factors of the cold front cloud system were summarized. [Result] The cloud formed by the cold front was in banded form in general. However, there was void in the cloud and its intensity was uneven. Most fast moving cold front was long and narrow banded echo and basically the radial velocity turned from northwest wind to southwest. With the changes of month, the feature of the reflective rate also changed. In winter, the cold front cloud was in layer form. The feature of the reflectivity factors was weak and in large area. However, the structure was loose and there was space in the echo. Among them, there were several strong echoes. Strong convection cell echo formed in the two sides of the cold front, and it moved with the entire cloud belt. When the dry cold front moved, regional strong convective current formed, mainly by convective cloud and small echo area. Generally, the changes of the wind direction can not be expounded from the radial velocity. However, the intensity of the convection cell was distinct, 'three-body scattering', 'side lobe echo', and 'weak echo', as well as features of super convection cell. [Conclusion] The study provided positive role for the application of Doppler radar in the surveillance of weather in Heilongjiang Province.
基金Supported by the National Natural Science Foundation of China under Grant Nos 91436211 and 11204086the National Basic Research Program of China under Grant No 2011CB921604the Shanghai Science and Technology Committee under Grant No 13PJ1402100
文摘We present a cold atom system with a dark-line two-dimensional magneto-optical trap, to increase the atomic density by suppressing the atomic radiation pressure. Optical depth （OD） and duty cycle are used to evaluate the system performance. We demonstrate a 100% increase in OD with the dark line, and obtain an ultrahigh OD of 264 with 10% for the duty cycle. Also, with an efficient dark line region, the OD could maintain above i00 with duty cycle as high as 30%. The cold atomic ensemble with an ultrahigh OD with a 10%-30% duty cycle is particularly advantageous in quantum i^formation processing and communication.
文摘晴空颠簸是影响飞机安全运行和旅客旅行舒适度的重要恶劣天气之一。为了研究2017年6月6日02:10(协调世界时)发生在山西省长治市上空的一次强烈的晴空颠簸事件的产生机制,本文使用常规观测资料、NOAA-15和NOAA-18卫星辐射资料并通过天气学分析和中尺度WRF数值模式以及GSI(Grid point Statistical Interpolation)同化系统同化等方法,对此次事件开展了数值模拟和机理研究。结果表明:该次飞机颠簸事件是一个典型的高空急流—锋区耦合系统导致的晴空湍流所致,高空急流是导致晴空湍流的主要因素之一。导致该次晴空湍流事件发生的是大气一系列要素对冷空气入侵的响应。高空冷云(冷空气)发展南下是促进此次强颠簸事件发生的重要诱因。由于高空冷云的南下,使得长治上空温度经向梯度增加,而长治上空温度经向梯度增加,使得中纬度风切变增大,增大的水平风垂直切变,导致理查森数(Ri)数值变小,而较小的Ri值是产生KH(Kelvin-Helmholtz)不稳定的必要条件,由于K-H不稳定导致了长治上空出现晴空湍流。此外,中尺度WRF模式以及GSI同化系统能够较好地模拟颠簸区附近的大气温度场特征,表明文中的数值预报流程对于大气温度、风场以及晴空湍流的发展具有一定的预报能力。
基金supported by the National Natural Science Foundation of China (Grant Nos.41575048 and 91637105)
文摘In this study, an east-moving Tibetan Plateau vortex(TPV) is analyzed by using the ERA-5 reanalysis and multi-source satellite data, including FengYun-2 E, Aqua/MODIS and CALIPSO. The objective is to demonstrate:(i) the usefulness of multi-spectral satellite observations in understanding the evolution of a TPV and the associated rainfall, and(ii) the potential significance of cloud-top quantitative information in improving Southwest China weather forecasts. Results in this study show that the heavy rainfall is caused by the coupling of an east-moving TPV and some low-level weather systems [a Plateau shear line and a Southwest Vortex(SWV)], wherein the TPV is a key component. During the TPV's life cycle, the rainfall and vortex intensity maintain a significant positive correlation with the convective cloud-top fraction and height within a 2.5?radius away from its center. Moreover, its growth is found to be quite sensitive to the cloud phases and particle sizes. In the mature stage when the TPV is coupled with an SWV, an increase of small ice crystal particles and appearance of ring-and U/V-shaped cold cloud-top structures can be seen as the signature of a stronger convection and rainfall enhancement within the TPV. A tropopause folding caused by ageostrophic flows at the upper level may be a key factor in the formation of ring-shaped and U/V-shaped cloud-top structures. Based on these results, we believe that the supplementary quantitative information of an east-moving TPV cloud top collected by multi-spectral satellite observations could help to improve Southwest China short-range/nowcasting weather forecasts.
基金supported by the National Natural Science Foundation of China(Grant Nos.42325503,42075063,42075066,and 42021004)the Hubei Provincial Natural Science Foundation and the Meteorological Innovation and Development Project of China(Grant No.2023AFD096)the Beijige Foundation of NJIAS(Grant No.BJG202304).
文摘The characteristics of summertime raindrop size distribution(DSD) and associated relations in the semi-arid region over the Inner Mongolian Plateau(IMP) were investigated,utilizing five-year continuous observations by a PARSIVEL2disdrometer in East Ujimqin County(EUC),China.It is found that only 7.94% of the 15 664 one-min precipitation samples meet classification criteria as convective rain(CR),but its contribution to the total rainfall amount is 63.87%.Notably,40.72% of the rainfall comes from large-sized raindrops(D> 3 mm),despite the fact that large-sized raindrops account for only 1.73% of the CR total number concentration.Further results show that the mean value of mass-weighted mean diameters(Dm) is larger(2.43 mm) and generalized intercepts(lgN_(W)) is lower(3.19) in CR,aligning with a "continentallike" cluster,which is mainly influenced by the joint impact of in-cloud ice-based processes and the below-cloud environmental background.Also,the empirical relationships of shape-slope(μ-Λ),radar reflectivity-rain rate(Z-R),and rainfall kinetic energy(KE_(time)-Rand KE_(time)-Z) are localized.To quantitatively analyze the impact of DSD parameters on kinetic energy estimation,power-law KE_(time)-R and KE_(time)-Z relationships are derived based on the normalized gamma distribution.N_(W)takes precedence over μ in affecting variabilities of multiplicative coefficients,especially for KE_(time)-R relationship where the multiplicative coefficient is proportional to N_(W)^(-0.287).It should be noted that although the proportion of CR occurring throughout the summer is small,raindrops with lower N_(W) and larger Dmwill generate higher KE_(time),which will bring a higher potential risk of soil erosion in semi-arid regions over IMP.
文摘对流云是南方人工增雨开发利用空中云水资源的重要对象,结构复杂多变;通过数值模式合理评估催化作业过程,进而研究其催化机制,是建立和改进催化作业技术的必要途径,也是评估实际人工增雨作业效果的有效手段。利用耦合了碘化银(AgI)催化的WRF(Weather Research and Forecasting)模式,对2021年5月4日福建古田人工增雨随机化试验个例开展催化模拟,分析AgI核化机制、催化对云系宏微观特征、降水机制的影响以及增雨效果评估。结果显示,AgI播撒后呈带状扩散,催化前期(09:00—11:00)(世界时,下同)地面降水增量缓慢增加;随后(11:00—13:00)降水增幅加大并出现剧烈波动;13:00后降水增量以负值为主。AgI主要核化机制为凝华核化,核化持续约40 min。AgI播撒后主要通过凝华核化使冰晶数浓度大幅增加(增量约3~9个·L^(-1)),增长的冰晶大部分转化为雪晶,再通过雪晶融化增加云中雨滴质量浓度。此次过程催化影响时间持续约4 h,催化部位绝对增雨量约-0.78~1.24 mm,增雨率约-8.3%~12.1%,总降水增量为4.64×10^(5) t,增雨效果显著。
