共查询到20条相似文献,搜索用时 62 毫秒
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In 1984, four climatic sequences combined to produce what may be a major anoxic catastrophe in the northern Chesapeake Bay, sufficient to severely threaten the major benthic species. These sequences are (i) the highest late-winter streamflow on record from the Susquehanna River watershed; (ii) streamflows from the Susquehanna River for the consecutive months of June, July, and August that are higher by 2 standard deviations than the respective monthly mean values measured over the last 34 years; (iii) a stationary high in August off the Atlantic Coast; and (iv) an absence of strong storm events in summer. An empirical equation is proposed for the prediction of the monthly trend of dissolved oxygen decrease in terms of a temperature-dependent subpycnoclinal respiration and a modified estuarine Richardson number. As of 23 August 1984, the summer pycnocline of the northern bay had eroded upward from its historically recorded depth below 10 meters to an abnormally shallow 5 meters, with higher stratification than in earlier years. Dissolved oxygen concentrations directly below the pycnocline decreased to zero during June, 2 months earlier than for previous wet years. At present, oxygen-deficient waters containing significant concentrations of hydrogen sulfide have penetrated into Eastern Bay and the Choptank and Potomac rivers. Because most remaining shellfish-spawning and seed-bed areas in these tributaries are located at depths between 4 and 8 meters, the continued absence of major destratifying events will prolong the present anoxic trend and may result in high benthic mortalities. 相似文献
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Hurricane debbie modification experiments, august 1969 总被引:1,自引:0,他引:1
Gentry RC 《Science (New York, N.Y.)》1970,168(3930):473-475
Maximum winds in Hurricane Debbie, August 1969, decreased after modification experiments by Project Stormfury. Clouds surrounding the center of Debbie were seeded with silver iodide particles five times at approximately 2-hour intervals on both 18 and 20 August. Before the first seeding on 18 August, the maximum speed of winds at 3600 meters was 182 kilometers per hour, but, 5 hours after the fifth seeding, these winds decreased to 126 kilometers per hour. On 20 August, the corresponding change was from 183 to 156 kilometers per hour. Analyses of the data suggest that the storm was modified. 相似文献
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Solar proton events: stratospheric sources of nitric oxide 总被引:1,自引:0,他引:1
The production of nitric oxide (NO) in the stratosphere during each of the solar proton events of November 1960, September 1966, and August 1972 is calculated to have been comparable to or larger than the total average annual production of NO by the action of galactic cosmic rays. It is therefore very important to consider the effect of solar proton events on the temporal and spatial distribution of ozone in the stratosphere. A study of ozone distribution after such events may be particularly important for validating photochemical-diffusion models. 相似文献
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Johnson TV Veeder GJ Matson DL Brown RH Nelson RM Morrison D 《Science (New York, N.Y.)》1988,242(4883):1280-1283
Infrared observations of Io during the 1986 apparition of Jupiter indicate that a large eruptive event occurred on the leading side of Io on 7 August 1986, Universal Time. Measurements made at 4.8, 8.7, and 20 micrometers suggest that the source of the event was about 15 kilometers in radius with a model temperature of approximately 900 Kelvin. Together with previously reported events, these measurements indicate that high-temperature volcanic activity on the leading side of Io may be more frequent than previously thought. The inferred temperature is significantly above the boiling point of sulfur in a vacuum(715 Kelvin) and thus constitutes strong evidence for active silicate volcanism on the surface of Io. 相似文献
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近48年海南省极端降水时空变化趋势 总被引:2,自引:0,他引:2
利用海南省16个地面观测站近48年的逐日降水资料,采用线性倾向估计和M-K方法,分析了海南省极端强降水事件的气候特征和变化趋势。结果表明,海南省区域平均的极端强降水日数的年变化为单峰型,8~10月为集中期。海南省极端强降水事件的持续时间以1d为主,最长持续时间达6d。近48年海南省区域平均的极端强降水量、极端强降水日数和强度均呈弱的增加或增强趋势,未发生突变。但极端强降水事件变化具有空间上的不一致,大部分地区表现为不同程度的增多趋势,局部地区增多趋势显著,并在80年代发生了突变。8和10月海南省极端降水量和降水强度的增多、增强使该时期区域性暴雨洪涝事件增多。 相似文献
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Paleomagnetic and (40)Ar/(39)Ar analyses from the Lathrop Wells volcanic center, Nevada, indicate that two eruptive events have occurred there. The ages (136 +/- 8 and 141 +/- 9 thousand years ago) for these two events are analytically indistinguishable. The small angular difference (4.7 degrees ) between the paleomagnetic directions from these two events suggests they differ in age by only about 100 years. These ages are consistent with the chronology of the surficial geological units in the Yucca Mountain area. These results contradict earlier interpretations of the cinder-cone geomorphology and soil-profile data that suggest that at least five temporally discrete eruptive events occurred at Lathrop Wells approximately 20,000 years ago. 相似文献
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2006-2010年通过"人工诱捕"和"天然捕获"的方法对贺江典型海弯水虱种群动态进行监测,评价生物防控的效果。结果显示:典型海弯水虱在4-6月的寄生数量最少;推测其生命周期为1a,6月是世代交替期,种群世代不重叠或重叠不明显;试验发现草鱼、青鱼、鲤能主动捕食典型海弯水虱。选择典型海弯水虱寄生数量最少的4-6月作为放流时间,于2007-2009年在贺江人工放流草鱼、青鱼、鲤156万尾;比较2006-2010年人工诱捕的典型海弯水虱的数量,发现从2008年开始,典型海弯水虱的数量逐年减少,2010年诱捕到的典型海弯水虱的数量比2006年减少85.1%;天然捕获贺江野生鲮和,发现在2009年9月至2010年8月,典型海弯水虱对鲮和的感染率、平均感染强度和平均密度均比2006年9月至2007年8月显著降低。以上结果初步表明生物防控取得了一定的效果。 相似文献
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Climate extremes: observations, modeling, and impacts 总被引:18,自引:0,他引:18
Easterling DR Meehl GA Parmesan C Changnon SA Karl TR Mearns LO 《Science (New York, N.Y.)》2000,289(5487):2068-2074
One of the major concerns with a potential change in climate is that an increase in extreme events will occur. Results of observational studies suggest that in many areas that have been analyzed, changes in total precipitation are amplified at the tails, and changes in some temperature extremes have been observed. Model output has been analyzed that shows changes in extreme events for future climates, such as increases in extreme high temperatures, decreases in extreme low temperatures, and increases in intense precipitation events. In addition, the societal infrastructure is becoming more sensitive to weather and climate extremes, which would be exacerbated by climate change. In wild plants and animals, climate-induced extinctions, distributional and phenological changes, and species' range shifts are being documented at an increasing rate. Several apparently gradual biological changes are linked to responses to extreme weather and climate events. 相似文献
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Epidemic strain of Venezuelan equine encephalomyelitis virus from a vampire bat captured in Oaxaca, Mexico, 1970 总被引:1,自引:0,他引:1
A vampire bat, Desmodus rotundus, captured in Oaxaca, Mexico, in August 1970, was found to be infected with the epidemic strain of Venezuelan equine encephalomyelitis virus at the same time that an equine epizootic was occurring there. 相似文献
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城市不透水区降雨径流量及径流水质变化规律研究 总被引:2,自引:0,他引:2
研究城市降雨径流量及径流水质对城市水文学理论扩充及城市雨水资源集蓄利用具有重要意义.通过对2010~2011年保定市区6~8月份降雨产流过程中屋面、路面等类型下垫面的降雨径流量及径流水质的同步监测,初步分析了城市降雨径流量及径流水质的变化规律.研究结果表明:不同屋面及路面降雨径流量与降雨量均呈现相关性显著的线性关系;城... 相似文献
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福建省水口水库网箱养殖鱼类大面积缺氧死亡原因分析 总被引:1,自引:0,他引:1
通过对2011年8-9月福建水口水库养殖鱼类大面积缺氧死亡事件期间不同水层溶解氧和水温变化趋势分析,并结合2004年以来水口水库多次发生的缺氧事件发生前和发生期间库区气象、水文等资料。分析发现:在汛期出现持续晴热、少雨的异常天气条件,水口水库会发生"耗氧"和"复氧"失衡,产生水体氧亏损现象;在随之出现的降水降温天气过程中下层缺氧水团上浮造成上层水体严重缺氧,养殖鱼出现大面积突发性缺氧死亡。 相似文献
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陕西省佛坪县地处秦岭南坡,是山地灾害频发的地区之一。其中以2002年6月9日及2007年8月30日2次山地灾害最为严重和典型,发生大量山体崩塌、河岸坍塌、滑坡及泥石流山地灾害事件,造成严重的人员、财产损失。通过野外实地考察研究,认为此次山地灾害的形成主要受地质因子、物质因子、地形地貌因子、人为活动因子等主导因素和暴雨诱发因素所影响。同时强调山地城市建设应尊重自然规律、科学规划、重视灾害环境评估、加强日常人为生产生活行为管理等是预防山地灾害发生、降低山地灾害损失的有效途径。 相似文献
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Rieger E Kanbach G Reppin C Vestrand WT Forrest DJ Chupp EL 《Science (New York, N.Y.)》1989,244(4903):441-444
Since launch in early 1980 the Gamma-Ray Spectrometer (GRS) onboard the Solar Maximum Mission (SMM) satellite has monitored the sun at gamma-ray energies. In addition to observations of solar flares, cosmic gamma-ray bursts, and precipitating radiation belt electrons, the instrument has detected a new class of high-energy transient events that cannot be attributed to any of these phenomena. The duration of these transients can range from 1 second to more than 10 minutes. The average event rate between 1980 and 1986 was about five per month. However, in February 1987 this rate increased by more than a factor of 25 and continued at this high level until June 1988. These transients can be subdivided into three classes: (i) 0.511-megaelectron volt annihilation line events, (ii) particle events, and (iii) broad-band photon continuum-like events. Evidence is presented that these transients are not of natural origin. It is found that the most likely sources of these events are reactors in earth orbiting satellites. Apart from the threat these reactors pose upon accidental reentry, the reactor-generated transients may have a deleterious effect on cosmic observations obtained with gamma-ray detectors in low earth orbit. 相似文献
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掌握昆虫群落及其与机场飞鸟的关系可以从生态学角度出发,通过控制昆虫的发生进而降低鸟击频率。通过对新桥国际机场昆虫群落连续3年的调查(2016—2018年,共鉴定30 102 头昆虫),发现群落由12目89科184种昆虫构成,半翅目和鞘翅目为优势类群,每年的6—8月是昆虫高发期。机场鸟类共记录6目19科39种,雀形目为优势类群,以食虫鸟和杂食鸟为主,活动高峰期是7—8月,与昆虫的高发期高度吻合。冗余分析进一步表明,杂食鸟和食虫鸟数量与昆虫生物量呈显著正相关,半翅目和鞘翅目是影响鸟类数量的主要昆虫类群。聚类分析揭示出新桥机场主要有3类生境,围界内草坪和围界外草地是防治的重点区域。这些研究结果为机场防范鸟击事件从传统的物理化学手段到生态综合治理的发展提供了思路。 相似文献
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研究以长春市4所高校的439名大学生为被试,经问卷调查,了解当代大学生的心理健康状况及应对方式特点,探讨生活事件、应对方式对大学生不良情绪的作用机制,结果表明:生活事件各因子与焦虑呈显著正相关,应对方式中除解决问题,其余5个因子与焦虑呈显著正相关。焦虑与抑郁之间也有显著正相关,而抑郁与生活事件和应对方式各因子的相关都未达到显著性水平,应对方式作为生活事件与焦虑的中介变量,在应激过程中,与生活事件协同作用于焦虑,中介效应显著。 相似文献
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After mass spawning events, coral embryos, lacking the protective capsule of other metazoans, are directly exposed to the environment at the ocean surface. Here, we present evidence that modest turbulence disrupts the integrity of these embryos, which fragment into totipotent cells that develop into proportionately smaller functional larvae. The level of turbulence required to fragment coral embryos can be generated from small wind-generated waves, which occur frequently during coral spawning on the Great Barrier Reef. The formation of planktonic coral clones, through natural embryo fragmentation of broadcast spawn, is a previously unknown mode of reproduction in the animal kingdom. 相似文献
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Tedesco EF 《Science (New York, N.Y.)》1979,203(4383):905-907
The lightcurves of the asteroids 49 Pales and 171 Ophelia bear a striking resemblance to those of eclipsing binary stars. This evidence suggests that these asteroids are binary objects. Asteroids belonging to the Themis dynamical family have unusual lightcurves, possibly due to satellite events; these unusual lightcurves suggest that multiple objects may be formed during the disruption of asteroids in collisional events. 相似文献
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阿勒泰地区夏季降水变化特征及其预测方法探讨 总被引:2,自引:0,他引:2
利用1961~2008年阿勒泰地区7个气象观测站的夏季(6~8月)降水资料,采用突变分析、小波分析等方法,对该地区夏季降水的时间变化特征进行诊断分析,并用谐波分析对阿勒泰地区夏季降水建立预测模型,进行试报和预报检验。结果表明:48 a来阿勒泰地区夏季降水有上升趋势,但是不明显;同时存在显著的8~10 a周期震荡;而且明显的突变点出现在1974年和1987年,其中1974~1987年降水为减少趋势,1987年后降水开始增多。谐波分析的预测模型对阿勒泰地区夏季降水预测效果较好,尤其是对极值的拟合效果比较好。 相似文献