中国不同地区气溶胶消光特性分析   总被引：14，自引：0，他引：14  

Zhang Junhu  Mao Jietai  Wang Meihua 《大气科学进展》2002,19(1):136-152

利用多波段太阳光度计在中国四个点（北京的密云，广东的新丰，青海的瓦里关，西藏的当雄）观测了４５０—９００ ｕｍ范围中多波长气溶胶光学厚度和Ａｎｇｓｔｒｏｍ指数。本文分析了这些参数从１９９８年２月到１９９９年１月这一年中的特点。结果表明，在干旱和半干旱地区，如密云（１７．１２°Ｅ，４０．６５°Ｎ）和瓦里关（１００．９０°Ｅ，３６．２９°Ｎ），春季出现气溶胶光学厚度的最大值，大约是其它季节的２倍。在湿润地区，如新丰（１１４．２°Ｅ，２４．５°Ｎ），虽然春季气溶胶光学厚度值也是最大，但只是比其它季节稍微大一些 瓦里关春季的Ａｎｇｓｔｒｏｍ指数有最小值，约０．１５，表明有比较大的粒子、密云和新丰的Ａｎｇｓｔｒｏｍ指数也有很大的月际变化。但没有明显的季节倾向。这表明，气溶胶的源比较复杂。  相似文献   

2007年冬季大连市区气溶胶垂直剖面特征          下载免费PDF全文

黄艇  宋煜  肖韶荣  盖晓波 《气象与环境学报》2009,25(4):31-35

选用2007年1月8—30日期间8个无云天的激光雷达资料进行分析。基于Fernald方法反演得到气溶胶消光系数廓线,结合无线电探空资料分析了边界层内气溶胶时空分布,并将反演的激光雷达最低观测高度处(180 m)的气溶胶消光系数与地面PM10、能见度资料进行对比分析。结果表明：冬季大连市区气溶胶主要分布在2 km以下区域,早晨和夜间在0.5 km以下区域经常存在一个气溶胶层;气溶胶消光系数廓线与探空资料较吻合;反演激光雷达最低观测高度处(180 m)的气溶胶消光系数与地面的PM10浓度呈正相关,与能见度呈负相关,相关性较好。  相似文献   

丽江高美古的大气消光系数测定     

张周生  陈培生  周吉光 《天文研究与技术》1996,(Z1)

１９９６年１－２月，我们用光电方法测定了丽江高美古在Ｂ、Ｖ两个波段的大气消光系数。为便于比较，在同一时期还测定了云南天文台凤凰山台址的大气消光系数。本文给出了观测结果，同时也列出了世界上一些天文台站的数据以供参考。  相似文献   

Intrabasin variability of the carbon-isotope record across the Permian–Triassic transition, Sverdrup Basin, Arctic Canada     

Stephen E. Grasby  Benoit Beauchamp   《Chemical Geology》2008,253(3-4):141-150

A major late Paleozoic depocentre, the Sverdrup Basin, Canadian High Arctic, has been largely left out of the latest Permian extinction debate, as early workers presumed Middle to Late Permian strata were absent. Basin-scale sequence-stratigraphic and chemostratigraphic correlations indicate Late Permian strata are only missing on the basin margins, where they were removed by sub-Triassic erosion, whereas continuous deposition is recorded in the basin centre. The varying degree of sub-Triassic erosion has significant impact on the carbon-isotope record across the Latest Permian Extinction event, where both the apparent rate and magnitude of carbon-isotope shift vary as a function of basin position. The intrabasin variability in apparent δ¹³C_org shift across the event is equivalent to that observed globally. In contrast to the abrupt isotope shifts recorded on the basin margin, similar to many records reported globally, the basin centre section shows a systematic shift associated with the Latest Permian Extinction. The Earth likely underwent a prolonged period of increasing environmental stress leading up to the event.  相似文献   

Supercontinent tectonics and biogeochemical cycle： A matter of ‘life and death＇     

M. Santosh 《地学前缘(英文版)》2010,1(1):21-30

<正>The formation and disruption of supercontinents have significantly impacted mantle dynamics,solid earth processes,surface environments and the biogeochemical cycle.In the early history of the Earth,the collision of parallel intra-oceanic arcs was an important process in building embryonic continents.Superdownwelling along Y-shaped triple junctions might have been one of the important processes that aided in the rapid assembly of continental fragments into closely packed supercontinents. Various models have been proposed for the fragmentation of supercontinents including thermal blanket and superplume hypotheses.The reassembly of supercontinents after breakup and the ocean closure occurs through "introversion","extroversion" or a combination of both,and is characterized by either Pacific-type or Atlantic-type ocean closure.The breakup of supercontinents and development of hydrothermal system in rifts with granitic basement create anomalous chemical environments enriched in nutrients, which serve as the primary building blocks of the skeleton and bone of early modern life forms. A typical example is the rifting of the Rodinia supercontinent,which opened up an N—S oriented sea way along which nutrient enriched upwelling brought about a habitable geochemical environment.The assembly of supercontinents also had significant impact on life evolution.The role played by the Cambrian Gondwana assembly has been emphasized in many models,including the formation of 'Trans-gondwana Mountains' that might have provided an effective source of rich nutrients to the equatorial waters,thus aiding the rapid increase in biodiversity.The planet has witnessed several mass extinction events during its history,mostly connected with major climatic fluctuations including global cooling and warming events,major glaciations,fluctuations in sea level,global anoxia,volcanic eruptions, asteroid impacts and gamma radiation.Some recent models speculate a relationship between superplumes,supercontinent breakup and mass extinction.Upwelling plumes cause continental rifting and formation of large igneous provinces.Subsequent volcanic emissions and resultant plume-induced "winter" have catastrophic effect on the atmosphere that lead to mass extinctions and long term oceanic anoxia.The assembly and dispersal of continents appear to have influenced the biogeochemical cycle,but whether the individual stages of organic evolution and extinction on the planet are closely linked to Solid Earth processes remains to be investigated.  相似文献   

Contemporary management issues confronting fisheries science     

Kenneth T. Frank  David Brickman 《Journal of Sea Research》2001,45(3-4)

Stock collapses have occurred worldwide. The most frequently cited cause is over-fishing, suggesting that fisheries management has been ineffective in controlling exploitation rates. The progression of a fishery from an over-exploited to a collapsed state involves impairment of the reproductive capacity of the target species, i.e. recruitment over-fishing. In many cases, this occurs by reduction of the spawning stock biomass (SSB) through the systematic elimination of spawning components within a stock complex. While operational definitions of minimum levels of SSB have been developed, they have seldom been applied and never adopted in a Canadian groundfish management context. The answer to the question of how much is enough to perpetuate a stock under exploitation has been illusive. Serebryakov [J. Cons. Int. Explor. Mer, 47 (1990) 267] has advocated definition of critical levels of SSB based on survival rates (R/SSB). We review his method and discuss the utility of the approach. An alternative approach to the problem of estimating minimum SSB is through a fundamental revision of the traditional stock and recruitment relationship. Explicit theoretical SSB thresholds below which reproduction/recruitment is severely impaired based upon density-dependent mating success (or Allee effects) is considered a superior approach to the question of how much is enough because of its ecological grounding. However, the successful application of this approach will require re-definition of the space/time scales of the management unit. Finally, support is growing for the establishment of closed areas or “no-take zones” as an alternative approach to managing the problems of fishing a stock complex by enabling sub-populations to escape fishing. While the expected benefits of areas protected from fishing are numerous, clear demonstrations of benefits of such areas in marine temperate ecosystems are lacking. In fact, unintended negative consequences may result from such actions.  相似文献   

省级MODIS植被指数序列的建立与应用     

张树誉  李登科  李星敏  高蓓 《山西气象》2006,(3):25-28

本文采用安德森分级采样直接获得的大气气溶胶质量密度换算成数密度。在此基础上,根据气溶胶数密度谱分布,验证了大气气溶胶的Junge谱与分段三参数谱相结合的谱模式。并且在得出气溶胶粒子谱基础上计算了大气气溶胶的散射、消光、吸收系数。  相似文献   

Latest Pleistocene paleoecology of Jefferson's ground sloth (Megalonyx jeffersonii) and elk-moose (Cervalces scotti) in northern Illinois     

Blaine W. Schubert  Russell Wm. Graham  Eric C. Grimm 《Quaternary Research》2004,61(2):231-240

New records of Jefferson's ground sloth (Megalonyx jeffersonii) and elk-moose (Cervalces scotti) from Lang Farm provide the first precise temporal correlation of these taxa with the specific environments inhabited by them near the time of their extinction. Six AMS ¹⁴C measurements establish an age of 11,405 ± 50 ¹⁴C yr B.P. for Lang Farm Cervalces and an age of 11,430 ± 60 or 11,485 ± 40 ¹⁴C yr B.P. for the Megalonyx. These measurements represent the youngest ¹⁴C dates for these two genera based on direct dating. Comparison of the dates with pollen data from northern Illinois indicates that these species inhabited a nonanalog environment that was transitional from mid-latitude tundra to mixed conifer and deciduous woodland. Although spruce (Picea sp.) was dominant, it was less abundant than prior to 12,500 ¹⁴C yr B.P. The presence of black ash (Fraxinus nigra) and fir (Abies sp.) indicates a wet climate and heavy winter precipitation. This may have been the preferred habitat for Cervalces because of its narrow geographic range. However, this habitat type was only one of many occupied by Megalonyx as indicated by its broad geographic distribution.  相似文献   

Phylogeny, diet, and habitat of an extinct ground sloth from Cuchillo Curá, Neuquén Province, southwest Argentina     

Michael Hofreiter  Julio L. Betancourt  Alicia Pelliza Sbriller  Vera Markgraf  H. Gregory McDonald 《Quaternary Research》2003,59(3):364-378

Advancements in ancient DNA analyses now permit comparative molecular and morphological studies of extinct animal dung commonly preserved in caves of semiarid regions. These new techniques are showcased using a unique dung deposit preserved in a late glacial vizcacha (Lagidium sp.) midden from a limestone cave in southwestern Argentina (38.5° S). Phylogenetic analyses of the mitochondrial DNA show that the dung originated from a small ground sloth species not yet represented by skeletal material in the region, and not closely related to any of the four previously sequenced extinct and extant sloth species. Analyses of pollen and plant cuticles, as well as analyses of the chloroplast DNA, show that the Cuchillo Curá ground sloth browsed on many of the same herb, grass, and shrub genera common at the site today, and that its habitat was treeless Patagonian scrub-steppe. We envision a day when molecular analyses are used routinely to supplement morphological identifications and possibly to provide a time-lapse view of molecular diversification.  相似文献   

不同相态的模式雹块对5.6cm雷达波散射及衰减特性的研究     

刘黎平  徐宝祥 《高原气象》1991,10(1):26-33

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