子午线收敛角与长度比的一种简捷算法

关于子午线收敛角和长度比的计算公式在许多大地测量书籍中都已导出,但精度要求不同,公式推导方法就不同.子午线收敛角和长度比计算是大地测量学中的常规计算,但其公式推导较复杂,初学者难以掌握.本文提出了一种子午线收敛角与长度比的简捷算法,本法公式推导简单,便于理解,编写了相应的计算程序,与传统方法解算结果相同.     

北太平洋副热带西部模态水异常与东亚中高纬度大气环流关系的一些新认识

根据1958-2001年SODA(Si mple Ocean Data Assi milation)海洋同化资料和NCAR/NCEP再分析资料,利用等密度面P-矢量计算法,分析探讨了北太平洋副热带西部模态水(简称STMW)季节演变和年际变化与前期东亚-北太平洋中高纬度大气环流异常的关系。分析指出:(1)STMW的体积具有显著的季节变化特征:4月体积最大、强度最强,夏秋逐渐减弱,12月体积最小、强度最弱。研究进一步指出,STMW体积的季节变化与西北太平洋中纬度地区的海表风应力及净热通量的季节演变过程紧密联系在一起,它在一定程度上反映了西北太平洋中纬度大气环流季节性演变的特征。(2)年际尺度上,5-7月STMW指数具有显著的3年左右的振荡周期,其年际变化不仅与海洋自身动力过程有关,还与前冬亚洲-太平洋中高纬度大气环流异常引起STMW形成区风应力动力混合及海表净热通量等因子异常有关:冬季东亚季风环流偏强(弱),STMW形成区洋面风应力的动力混合作用及海表热力蒸发加强(减弱),使得海洋对流混合加强(减弱),进而加强(抑制)了混合均匀的低位涡水体进入温跃层,随着季节演变,造成5-7月STMW强度加强(减弱)。5-7月S...     

动态冠层模型ICM的改进及其对中高纬地区植被季节和年际变化的模拟试验

植被动态冠层模型Interactive Canopy Model(ICM)考虑了生态系统中较完整的碳氮循环过程,能够较为客观真实地描述较短时间尺度上植被的动态变化特征.本文在ICM原有碳氮分配方案基础上,考虑了植物花、果实等新生组织对碳氮分配的影响,假设新生组织碳库是花期以后植物的主要碳汇之一,并利用物候模型Fore-...     

Response of a mid‐latitude cirque glacier to climate over the last two decades: Mangaehuehu Glacier,Mt Ruapehu

The recent loss of mountain glaciers in response to climate warming has been reported across a range of latitudes globally, but the processes involved are not always straightforward. In southern Pacific mid‐latitudes, twentieth‐century glacier fluctuations are thought to reflect the strength of westerly atmospheric circulation, which brings increased precipitation, leading to mass gains. We present a study of the response of Mangaehuehu Glacier, a cirque glacier on Mt Ruapehu, to climate over the last two decades. Glacier surface area fluctuated in size over this period, corresponding closely with mean end‐of‐summer snowlines in the Southern Alps. The key control on glacier extent appears to be ablation season temperature, itself controlled by regional atmospheric circulation, including El Niño‐Southern Oscillation, Interdecadal Pacific Oscillation (IPO), and to a lesser extent, Southern Annular Mode (SAM). Copyright © 2011 John Wiley & Sons, Ltd.     

2005年6月东亚夏季风活动异常及其影响机制初步分析

应用欧洲中心（ECMWF）N日08时客观分析资料、中国测站降水资料、OLR资料和NCEP2再分析资料以及国家气象中心提供的1976～2006年的逐日西太平洋副热带高压脊线位置，利用合成分析、小波分析和带通滤波等方法，初步分析了2005年东亚夏季风的活动特征和影响机制。结果发现2005年6月东亚夏季风活动出现明显异常，其中31～32候季风前沿异常停留在南海-菲律宾一带以及华南西部，33～35候季风前沿停滞在华南地区，较常年明显偏南，造成了我国华南洪涝；36候季风前沿跳至黄淮地区，导致长江空梅、黄淮地区多雨。进一步研究发现西太平洋副热带高压和中高纬槽脊活动异常及热带和中高纬度低频振荡是导致2005年6月东亚夏季风异常的主要原因。     

Generalization of the Lambert–Lagrange projection

The Lagrange projection represents conformally the terrestrial globe within a circle. This is achieved by compressing the latitude and longitude and by applying the new coordinates into the equatorial stereographic projection. The same concept can be generalized to any conformal projection, although the application of this technique to other analytical functions is less known. In this work, the general Lambert–Lagrange projection formula is proposed and the application of the modified coordinates is discussed on projections: stereographic, conformal conic and Gauss–Schreiber. In general, the results are merely a curiosity, except for the case of Gauss–Schreiber, where the use of coordinates with altered scale can be applied in the optimization of conformal projections.     

Change detection for 3D vector data: a CGA-based Delaunay–TIN intersection approach

In this paper, conformal geometric algebra (CGA) is introduced to construct a Delaunay–Triangulated Irregular Network (DTIN) intersection for change detection with 3D vector data. A multivector-based representation model is first constructed to unify the representation and organization of the multidimensional objects of DTIN. The intersection relations between DTINs are obtained using the meet operator with a sphere-tree index. The change of area/volume between objects at different times can then be extracted by topological reconstruction. This method has been tested with the Antarctica ice change simulation data. The characteristics and efficiency of our method are compared with those of the Möller method as well as those from the Guigue–Devillers method. The comparison shows that this new method produces five times less redundant segments for DTIN intersection. The computational complexity of the new method is comparable to Möller’s and that of Guigue–Devillers methods. In addition, our method can be easily implemented in a parallel computation environment as shown in our case study. The new method not only realizes the unified expression of multidimensional objects with DTIN but also achieves the unification of geometry and topology in change detection. Our method can also serve as an effective candidate method for universal vector data change detection.     

Environmental assessment from the sedimentary record of high-latitude fiords

The sedimentary record of fiords at high latitude where global change may be occurring earliest and will be greatest has the potential for assessment of environmental change at both low resolution (the scale of millennia) and high resolution (decadal to less than daily). Unlike the lacustrine record which has been used very successfully in these studies, the sedimentary processes and thus the sedimentary deposits of fiords differ (1) in the role of salt water in inhibiting mixing and promoting flocculation, and through the role of sea-ice, (2) in the exchange of mass and energy with the much larger ocean beyond, and (3) in the role of benthic biota in the sedimentary environment. The work reviewed in this paper shows that fiord sediments are being used to assess sedimentary and oceanic processes, as well as glacial, periglacial and geomorphic history, and that they are important proxies for long-term climate and hydrology. Recommendations for advancing this work include long-term monitoring of conditions in fiords and their drainage basins so that the transfer relations can be more solidly constructed from the proxy of fiord sediment. Integration of results from fiords in opposite polar latitudes, and among proxies especially from lacustrine and ice-core records will produce valuable insights. Assessment of the range of conditions in fiords from the most polar to temperate regions is important to building models of their processes and understanding of the paleoenvironmental signals that can be interpreted from each type.     

Abrupt vegetation changes during the last glacial to Holocene transition in mid‐latitude South America

A pollen record from the Huelmo site (ca. 41°30′S) shows that vegetation and climate changed at millennial time‐scales during the last glacial to Holocene transition in the mid‐latitude region of western South America. The record shows that a Nothofagus parkland dominated the landscape between 16 400 and 14 600 ¹⁴C yr BP, along with Magellanic Moorland and cupressaceous conifers. Evergreen North Patagonian rainforest taxa expanded in pulses at 14 200 and 13 000 ¹⁴C yr BP, following a prominent rise in Nothofagus at 14 600 ¹⁴C yr BP. Highly diverse, closed canopy rainforests dominated the lowlands between 13 000 and 12 500 ¹⁴C yr BP, followed by the expansion of cold‐resistant podocarps and Nothofagus at ca. 12 500 and 11 500 ¹⁴C yr BP. Local disturbance by fire favoured the expansion of shade‐intolerant opportunistic taxa between 10 900 and 10 200 ¹⁴C yr BP. Subsequent warming pulses at 10 200 and 9100 ¹⁴C yr BP led to the expansion of thermophilous, summer‐drought resistant Valdivian rainforest trees until 6900 ¹⁴C yr BP. Our results suggest that cold and hyperhumid conditions characterised the final phase of the Last Glacial Maximum (LGM), between 16 400 and 14 600 ¹⁴C yr BP. The last ice age Termination commenced with a prominent warming event that led to a rapid expansion of North Patagonian trees and the abrupt withdrawal of Andean ice lobes from their LGM positon at ca. 147 000 ¹⁴C yr BP. Hyperhumid conditions prevailed between 16 400 and 13 000 ¹⁴C yr BP, what we term the ‘extreme glacial mode’ of westerly activity. This condition was brought about by a northward shift and/or intensification of the southern westerlies. The warmest/driest conditions of the last glacial–interglacial transition occurred between 9100 and 6900 ¹⁴C yr BP. During this period, the westerlies shifted to an ‘extreme interglacial mode’ of activity, via a poleward migration of stormtracks. Our results indicate that a highly variable climatic interval lasting 5500 ¹⁴C years separate the opposite extremes of vegetation and climate during the last glacial‐interglacial cycle, i.e. the end of the LGM and the onset of the early Holocene warm and dry period. Copyright © 2003 John Wiley & Sons, Ltd.     

ZONALITY OF DISTRIBUTION OF PHYSICO-GEOGRAPHICAL ZONES IN CHINA

With the methods of regression analysis and trend surface analysis, taking the bottom and top lines of dark conifer forest, bottom line of permafrost and the snowline of the latest glaciation in China as examples, this paper discusses the zonality regulaties of the distribution of physico-geographical zones in China. (1) Latitude zonality obeys the mathematical model of normal frequency distribution, being approximate to descending straightly within the latitude of China. (2) Longitude zonality shows that the elevation of physico-geographical zone rises straightly with the distance to east coast. (3) The combination of latitude and longitude zonalities appears a plane inclining from SSW to NNE. The decline of physico-geographical zone resembles a semiellipse- sphere inclining from the Qinghai-Xizang (Tibet) Plateau to northeast China, reflecting the effect of relief. (5) Physico-geographical zonation depends on the combination of hydrothermal conditions. Thus the factors influencing the distribution reg