关于变形极坐标法定点问题的探讨   总被引：2，自引：0，他引：2  

孙建华  谭校山 《测绘工程》2003,12(1):55-57

对变形极坐标法定点问题（危险区域、多值或双值解），根据规范和待定点P的性质，排除危险区域、多值或双值解的产生，论证对变形极坐标法定点的可行性、实用性。  相似文献   

Lagrangian Estimations of Ozone Loss in the Core and Edge Region of the Arctic Polar Vortex 1995/1996: Model Results and Observations     

A. N. Lukyanov  H. Nakane  V. A. Yushkov 《Journal of Atmospheric Chemistry》2003,44(2):191-210

Ozone evolution and diabatic descent in the Arctic polar vortex in winter 1995/1996 was studied with a newly developed diabatic trajectory–chemistry model (DTCM). To study the chemical and dynamic evolution of the species in the polar vortex, 400 diabatic trajectories were calculated in the vortex core and edge region by using three-dimensional (3-D) wind data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). The averaged diabatic descending motion and ozone behavior were obtained for particles started from the core and from the edge region of the vortex. The difference in ozone-loss rates as well as the difference in descending rates between the vortex core and the vortex-edge region was not statistically significant. The average cumulative ozone loss of 65 ± 16% in the vortex core obtained from the model calculations was consistent with the estimates obtained with a different method (Match experiment). The model results for the vortex core were compared with those obtained using trajectories with the vertical winds calculated on the basis of radiative cooling rates as used by the SLIMCAT 3-D chemical transport model. Although the trajectories based on cooling rates exhibited lower descending rates than those based on 3-D analyzed wind data, the ozone behavior was similar for both types of trajectory. Ozonesonde data from two stations (Ny-Alesund in the vortex core and Yakutsk in the vortex edge) were compared with the model results. For Lagrangian estimation of the ozone loss at these stations, the descending rates obtained by the diabatic trajectory calculations were used. Good agreements were obtained between the model results and observations for both the vortex core and edge region. These results suggest that strong ozone depletion occurred not only in the core, but also in the edge region of the vortex, and that air masses from the mid-latitudes did not appreciably affect the degree of ozone depletion in this winter–spring period. The sensitivity of the model to different descending rates and to the presence of large nitric acid trihydrate (NAT) particles was also examined.  相似文献   

Measurement of Halogenated Dicarboxylic Acids in the Arctic Aerosols at Polar Sunrise     

M. Narukawa  K. Kawamura  H. Hatsushika  K. Yamazaki  S.-M. Li  J. W. Bottenheim  K. G. Anlauf 《Journal of Atmospheric Chemistry》2003,44(3):323-335

Halogenated dicarboxylic acids, such as bromomalonic (Br-C₃), chlorosuccinic (Cl-C₄) and bromosuccinic (Br-C₄) acids, have been measured, for the first time, in the arctic aerosols during the polar sunrise experiment ALERT2000 (February to May). They were detected in the light spring, but not in the dark winter. Concentration ranges of halogenated diacids in the spring were 0.11–0.68 ng m^–3 for Br-C₃ diacid, 0.04–0.10 ng m^–3 for Cl-C₄ diacid and 0.12–0.20 ng m^–3 for Br-C₄ diacid. Those of Br-C₃ diacid increased from late April to early May, whereas Cl-C₄ diacid decreased. In contrast, Br-C₄ diacid showed maximum concentrations in the middle of the experiment. A strong negative correlation (R = –0.98) was obtained between Br-C₃ and Cl-C₄ diacids. Concentrations of methanesulfonic acid (MSA) also increased from late April to early May whereas those of Cl^– ion decreased. A strong positive correlation was found between Cl-C₄ diacid and Cl^– ion (R = 0.99) and between Br-C₃ diacid and MSA (R = 0.96). These results suggest that Br-C₃ diacid is primarily derived from marine biogenic source, whereas Cl-C₄ diacid is secondarily formed by heterogeneous reaction involving halogen chemistry on sea salt. Satellite images of sea ice concentrations and backward air mass trajectories suggest that the aerosols containing halogenated diacids were transported over the sampling sites from the Arctic Ocean covered with sea ice.  相似文献   

Physical properties of aerosols at Maitri,Antarctica     

C. G. Deshpande  A. K. Kamra 《Journal of Earth System Science》2004,113(1):1-25

Measurements of the submicron aerosol size distribution made at the Indian Antarctic station, Maitri (70‡45′S, 11‡44′E) from January 10th to February 24th, 1997, are reported. Total aerosol concentrations normally range from 800 to 1200 particles cm⁻³ which are typical values for the coastal stations at Antarctica in summer. Aerosol size distributions are generally trimodal and open-ended with a peak between 75 and 133 nm and two minima at 42 and 420 nm. Size distributions remain almost similar for several hours or even days in absence of any meteorological disturbance. Total aerosol concentration increases by approximately an order of magnitude whenever a low pressure system passes over the station. Based on the evolution of aerosol size-distributions during such aerosol enhancement periods, three types of cases have been identified. The nucleation mode in all three cases has been suggested to result from the photochemical conversion of the DMS emissions transported either by the marine air or by the air from the ice-melt regions around Maitri. Subsidence of midtropospheric air during the weakening of radiative inversion is suggested as a possible source of the nucleation mode particles in the third case. Growth of the nucleation mode particles by condensation, coagulation and/or by cloud processes has been suggested to be responsible for other modes in size distributions.  相似文献   

清江隔河岩两级升船机中间渠道及下游引航道船舶牵引方式优化方案     

姜亚庄  贺德斌 《岩土力学》2003,(Z1)

清江隔河岩升船机系统,原设计规划配置4艘消拖船用于推(拖)无动力分节驳进出两级垂直升船机,由于原设计考虑的条件与实际情况差异极大,势必会造成设备利用率低,并且,消拖船投入运行后还要产生难以承受的维修费用和人员成本。为此,提出了一种岸边牵引方式,对无动力分节驳进出升船机是一种既经济、又有效的优化方案。  相似文献   

A Late Cretaceous pole for the Pacific plate: implications for apparent and true polar wander and the drift of hotspots   总被引：1，自引：0，他引：1  

Rory D. Cottrell  John A. Tarduno   《Tectonophysics》2003,362(1-4):321-333

We present a Late Cretaceous (81 Ma) pole position for the Pacific plate derived from paleomagnetic analyses of basalt samples from Detroit Seamount (of the Hawaiian–Emperor seamounts) that were oriented using Brunhes-age overprints. This pole is at much higher latitudes than the previously published Late Cretaceous pole positions based on the modeling of magnetic anomalies observed during marine surveys over seamounts. Our new pole suggests that the Pacific plate would have moved rapidly between 95 and 81 Ma at speeds as high as 19.8 (−10.8/+11.2) cm/year. The Pacific plate at this time was smaller than the present-day plate and had a substantial subducting boundary. The high-velocity estimates are comparable with those of other paleoplates having similar characteristics. Therefore, plate tectonic driving forces can explain the motion and there is no need to invoke true polar wander. Decreases in mantle drag associated with vigorous Late Cretaceous volcanism in the Pacific, however, may have contributed to the rapid plate speed. The new pole position, together with other reliable paleomagnetic indicators of Pacific apparent polar wander, further supports the notion of drift of the Hawaiian hotspot during the Late Cretaceous.  相似文献   

川北旺苍-南江地区晚侏罗世古地磁学研究与真极移的探讨   总被引：1，自引：0，他引：1       下载免费PDF全文

白立新  朱日祥  吴汉宁 《地球物理学报》1998,(3)

本文对四川北部旺苍-南江地区晚侏罗世蓬莱镇组进行了较为详细的岩石磁学和古地磁学研究．逐步热退磁揭示出蓬莱镇组岩石所携带的剩磁由两个分量组成,其中低温组分（次生剩磁）的解阻温度低于420℃;高温组分（特征分量）可通过褶皱及倒转检验,由此求得磁偏角和磁倾角分别为18．4°和29．3°（构造校正后）,95％置信回（α95）为8．5°,对应的古地磁极经纬度分别为236．4°E和66．6°N．基于古地磁结果,并结合已有的地质证据,提出根据古地磁学确定的扬子地块晚侏罗世古纬度偏低的原因可能是由真极移造成的．  相似文献   

A Bootstrap Test Using Maximum Likelihood Ratio Statistics to Check the Similarity of Two 3-Dimensionally Oriented Data Samples     

Sojen Joy  Snigdhansu Chatterjee 《Mathematical Geology》1998,30(3):275-284

Comparing three-dimensionally oriented datasets is a problem encountered in various branches of earth science. A simple statistical tool for the comparison of two 3-dimensionally oriented datasets using the bootstrap method in line with the usual nonparametric permutation test is described here. This bootstrap test involves the estimation of maximum likelihood ratio statistic for properly constructed joint frequency tables of the datasets to be compared. This test does not use asymptotic result and will work well even for small sample sizes. Also this test does not make any specific distributional assumptions.  相似文献   

Imaging of structures in the high-latitude ionosphere: model comparisons     

D. W. Idenden  R. J. Moffett  M. J. Williams  P. S. J. Spencer  L. Kersley 《Annales Geophysicae》1998,16(8):969-973

The tomographic reconstruction technique generates a two-dimensional latitude versus height electron density distribution from sets of slant total electron content measurements (TEC) along ray paths between beacon satellites and ground-based radio receivers. In this note, the technique is applied to TEC values obtained from data simulated by the Sheffield/UCL/SEL Coupled Thermosphere/Ionosphere/Model (CTIM). A comparison of the resulting reconstructed image with the input modelled data allows for verification of the reconstruction technique. All the features of the high-latitude ionosphere in the model data are reproduced well in the tomographic image. Reconstructed vertical TEC values follow closely the modelled values, with the F-layer maximum density (NmF2) agreeing generally within about 10%. The method has also been able successfully to reproduce underlying auroral-E ionisation over a restricted latitudinal range in part of the image. The height of the F2 peak is generally in agreement to within about the vertical image resolution (25 km).  相似文献   

南海海温异常对华南气候影响的数值研究   总被引：6，自引：3，他引：6  

冯瑞权  吴池胜  王安宇  古志明  侯尔滨  唐天毅 《热带气象学报》2004,20(1):32-38

采用NCEP／NCAR再分析的500hPa高度场、海温场(SST)、极冰资料，分析讨论了登陆广东省热带气旋活动异常与大气环流、极冰、SST、各种环流指数等影响因子之间的关系，得到登陆广东省热带气旋(TC)偏多、偏少年对应的大气环流、极冰、SST、各种环流指数的概念模型。分析结果表明：(1)亚欧大陆在秋、冬季中高纬度以经(纬)向环流为主，则次年登陆广东省的TC偏多(少)；(2)赤道东太平洋SST对热带气旋的影响最稳定和最明显，当1～4月赤道东太平洋SST偏暖(冷)时，当年登陆广东省的TC偏少(多)，次年登陆的TC偏多(少)；(3)夏、秋、冬季多(少)冰年，或者秋冬季连续多(少)冰年时，登陆热带气旋多为正常偏少(多)。  相似文献