多层界面快速反演在高精度石油重力勘探中的应用

重力勘探作为一种快速普查方法，在深部地质构造研究、区域地质构造划分及找矿勘探中均已取得显著的地质效果。自８０年代后期，由于在重力测地工作中使用红外测距仪及高精度ＧＰＳ定位技术，确保了重力测点位置及高程有较高的精度；在重力观测中普遍采用目前世界上精度最高的Ｌａｃｏｓｔｅ型重力仪进行基点联测，采用对恒温系统改进后的Ｗｏｒｄｅｎ重力仪进行重力测点观测，使得重力测量的质量及精度都有了很大提高，为扩大重力法的应用提供了条件。本文给出的一例是；在我国某含油沉积盆地上，根据对实测１：２５０００高精度重力资料（布格重力异常总观测均方误差：６０×１０￣－８ｍ／ｓ￣２）的处理及约束信息下多层界面反演结果，确定有利油气聚集的圈闭范围，推断含油层的大致规模。     

Position and velocity reliability testing in degraded GPS signal environments

Reliability testing, namely receiver autonomous integrity monitoring (RAIM), consists of statistical testing of least-squares residuals of observations, e.g., on an epoch-by-epoch basis aiming towards reliable navigation fault detection and exclusion (FDE). In this paper, classic RAIM and FDE methods are extended with testing of range-rate residuals to find inconsistent velocity solutions in order to contribute to the reliability of the system with special focus on degraded signal environments. Reliability enhancement efforts discussed include a Backward-FDE scheme based on statistical outlier detection and an iteratively reweighted robust estimation technique, a modified Danish method. In addition, measurement weighting assigned to code and Doppler observations is assessed in the paper in order to allow fitting a priori variance models to the estimation processes. The schemes discussed are also suitable in terms of computational convenience for a combined GPS/Galileo system. The objective of this paper is to assess position and velocity reliability testing and enhancement in urban and indoor conditions and to analyze the navigation accuracy conditions with high sensitivity GPS (HSGPS) tests. The results show the necessity of weighted estimation and FDE for reliability enhancement in degraded signal-environment navigation.     

The extent of desertification on Saudi Arabia

Desertification is the process that turns productive deserts into non-productive deserts as a result of poor land-management. Desertification reduces the ability of land to support life, affecting wild species, domestic animals, agricultural crops and humans. The reduction in plant cover that accompanies desertification leads to accelerated soil erosion by wind and water. South Africa is losing approximately 300–400 million tons of topsoil every year. As vegetation cover and soil layer are reduced, rain fall impact and run-off increases. This paper discusses the extent of desertification, its potential threat to sustained irrigated agriculture and possible measures adopted to control ongoing desertification processes to minimize the loss of agricultural productivity in an arid country such as the Kingdom of Saudi Arabia.     

海底热流长期观测系统研制进展

浅海和俯冲海沟等海域,不仅是矿产和油气资源主潜力区,也是构造地震频发区,其浅表热流和深部温度信息对于了解板块俯冲和岩浆活动等过程至关重要.这些区域浅层地温场和热流场受到底水温度波动(BTV)强烈扰动,其背景热流需由长期观测来获取.在全面分析了国内外海底热流长期观测技术特点后,我们提出了系缆式海底热流长期观测方案,201...     

High Asia cryospheric observation: a proposed network under Global Cryosphere Watch (GCW)

In coordination with Global Cryosphere Watch (GCW) initiated by World Meteorology Administration (WMO), a regional observation network is proposed based on existing stations/sites over High Asia and cryospheric elements required by GCW. Thus, High Asian Cryosphere (HAC) network is preliminary designed, composing of seven "supersites", each containing several reference sites. The network covers major mountain ranges in High Asia, such as East Tianshan, Qilian, Tanggula, Nyainqentanglha, Himalayas as well as the central and eastern Qinghai-Xizang (Tibet) Plateau. Although multiple cryospheric elements were observed at the existing HAC network, many others, which are required by Integrated Global Observation System-Cryosphere Theme (IGOS-Cryosphere), are not yet included. More comprehensive observations are necessary to be included into "supersites" of HAC, so that the basic requirements for validation of satellite data, assimilation and coupled regional models can be met.     

Bimodality of the South Asia High simulated by coupled models

The observed South Asia High (SAH) center is characterized by two distinctive equilibrium modes during boreal midsummer, namely the center of SAH is located between 82.5^o--92.5^oE for the Tibetan Plateau mode and between 55^o--65^oE for the Iranian Plateau mode, respectively. The present study describes the ability of 15 coupled general circulation models (CGCM) used in the Intergovernmental Panel on Climate Changes (IPCC) 4th Assessment Report to reproduce the observed bimodality of the SAH. These models reveal a wide range of skill in simulating this bimodality. Nearly half of the models reproduced the bimodality, while the other half of the models did not simulate well these two modes whereas usually preferring one mode. The models that reproduced the bimodality of the SAH present similar horizontal and vertical circulations as those features from the NCEP reanalysis data. The results from these models identify the warm characteristics of the SAH and indicate that these two modes have different dynamic and thermodynamic properties. Different characteristics of the simulated sensible heat and latent heat related to precipitation partly contribute to the difference in the simulations of the SAH bimodality. The majority of these models that prefer to simulate the Tibetan Plateau mode produce a small sensible heat flux difference between the Iranian Plateau and the Tibetan Plateau, and also generally simulate a very strong false precipitation center over the east of the Tibetan Plateau, which indicates strong latent release and thereby contributes to the preference of the SAH center on the Tibetan Plateau. Whereas, the models that reproduce the bimodality of the SAH tend to simulate large precipitation over the southern Himalayas and no obviously false precipitation is produced over the east of the Tibetan Plateau. In addition, the models resolution may also have important impacts on the simulations of precipitation.     

北极海冰对2008年1月乌拉尔高压异常的影响

2008年1月我国南方发生了大范围的雨雪冰冻灾害天气,造成此次灾害的一个重要原因是乌拉尔高压异常的长期维持,而作为下垫面的海洋,2007/2008冬季环北欧海海冰异常偏少。观测资料合成分析表明,乌拉尔山地区出现高压异常与巴伦支海和喀拉海的海冰偏少存在密切对应关系。利用大气环流模式试验研究了(90°W~60°E)区域海冰异常对大气的影响,模拟结果显示海冰对乌拉尔高压异常有正的贡献,线性模式诊断表明天气尺度瞬变波是海冰影响乌拉尔高压异常的一种重要机制。     

REASONS FOR THE LATE ONSET AND ANOMALOUS SOUTHWARD PERSISTENCE OF THE SOUTH CHINA SEA SUMMER MONSOON IN 2005

Features of atmospheric circulation and thermal structures are discussed using the NCAR/NCEP data to reveal the reasons for the late onset and anomalous southward persistence of the South China Sea Summer Monsoon (SCSSM) in 2005. The results show that three factors are crucial. First, a strong Arabian High overlaps with a high-latitude blocking high and channels strong cold air to southern Asia. Second, the Tibetan Plateau has a bigger snow cover than usual in spring and the melting of snow cools down the surface. Third, the Somali Jet breaks out at a much later date, being not conducive to convection over Indochina. The former two factors restrict atmospheric sensible heating over the Tibetan Plateau and nearby regions while the third one limits latent heating over Indochina. All of the factors slow down atmospheric warming and postpone the onset of SCSSM. Long after the onset of SCSSM, strong cold air over India advances the Southwest Monsoon northward slowly, resulting in weaker convection and latent heating over the Tibetan Plateau and nearby areas. The negative feedback conversely inhibits further northward movement of Southwest Monsoon.     

SEASONAL PERSISTENCE OF THE WEST PACIFIC SUBTROPICAL HIGH AND ITS RELATIONSHIP WITH THE SURFACE HEAT FLUX ANOMALY

This paper investigates the interannual variation of the West Pacific Subtropical High (WPSH) intensity based on the data compiled by the Chinese National Climate Center. Monthly reanalysis data from National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) are also used to study the lead-lag relationship between WPSH intensity and surface heat flux anomalies. The three major findings are as follows: First, WPSH intensity presents good seasonal persistence, especially from winter to the ensuing summer. Persistence is more significant after 1977, especially from spring to summer, and from summer to autumn; persistence of anticyclonic anomalies are significantly better than cyclonic anomalies. Second, surface heat flux tends to present opposite anomalous patterns between the strong and weak years of the WPSH intensity, which is especially valid at the latent heat flux over the ocean. Simultaneous correlations between surface heat flux and WPSH intensity in each of the seasons are marked by similar key areas. Finally, surface heat flux from the preceding winter of a strong summer WPSH is quite similar to strong spring WPSH, but the positive anomalies over the northwest Pacific and south of Japan are notably stronger. The situations in the weak years are similar except for those over the northwest Pacific: winter surface heat flux shows negative anomalies for a weak spring WPSH, but positive anomalies for a weak summer WPSH. It is suggested that surface heat flux in the previous winter plays an important role in maintaining the WPSH intensity in the ensuing spring and summer.     

华南地区汛期极端降水的概率分布特征

利用1960-2005年华南地区71个测站的逐日降水量资料和NCEP/NCAR南半球月平均海平面气压场再分析资料,采用Le Page榆验、广义极值分布等统计诊断方法,研究了华南地区近46 a前汛期(4-6月)和后汛期(7-9月)极端降水的时空变化及概率分布特征.并讨论了南半球澳大利亚高压和马斯克林高压强度指数与华南汛期暴雨日数间年代际变化的关系.结果表明:(1)1992年华南地区降水发生了由减少趋势到增多趋势的突变,降水趋势发生突变后前汛期极端降水量和日极端降水强度有所下降,而后汛期则是显著增强.(2)华南汛期年平均日最大降水量、50 a一遇日最大降水量极值和暴雨日数的空间分布特征相似,即前汛期的空间分布自南向北呈现"低-高-低"的分布趋势,后汛期呈现由沿海到内陆的"高-低"的分布趋势.(3)1992年发生突变后,前、后汛期年平均日最大降水量和年平均暴雨日数显著增加和减少的空间分布基本一致.(4)就年代际变化而言,南半球澳大利亚高压和马斯克林高压的强度变化是华南汛期降水异常的重要气候背景,即当两高压处在同时增强时期时,华南前汛期极端降水处于偏少阶段,后汛期则处于偏多阶段.