基于静稳天气下气球探空实验的中国沙漠地区沙尘气溶胶的垂直分布（英文）          下载免费PDF全文

HABIB Ammara  CHEN Bin  SHI Guangyu  IWASAKA Yasunobu  NATH Debashis  KHALID Bushra  TAN Saichun  MAHMOOD Tariq  JIAO Reguang  NTWALI Didier 《大气和海洋科学快报》2019,(1):12-20

塔克拉玛干沙漠是亚洲沙尘气溶胶的重要源地。为探讨塔克拉玛干地区沙尘气溶胶的理化特性与时空变化,研究其环境与气候效应,本文分析了四个季节在中国敦煌(塔克拉玛干沙漠内)取得的探空气球观测数据,包括气溶胶的数浓度、粒径分布、质量浓度及在西风主导下的水平输送通量。气溶胶数浓度的垂直廓线显示,来自沙漠地区的矿物粒子对局地环境与气候有重要影响,且所有季节都存在长距离输送。粒子谱分布显示局地有大量粗粒子输入。结果说明,源于塔克拉玛干沙漠的沙尘气溶胶的背景输送有着重要的科学意义,需进一步研究其对东亚和西太平洋地区环境与气候的影响。  相似文献   

Wide‐azimuth angle gathers for anisotropic wave‐equation migration     

Paul Sava  Tariq Alkhalifah 《Geophysical Prospecting》2013,61(1):75-91

Extended common‐image‐point gathers (CIP) constructed by wide‐azimuth TI wave‐equation migration contain all the necessary information for angle decomposition as a function of the reflection and azimuth angles at selected locations in the subsurface. The aperture and azimuth angles are derived from the extended images using analytic relations between the space‐ and time‐lag extensions using information which is already available at the time of migration, i.e. the anisotropic model parameters. CIPs are cheap to compute because they can be distributed in the image at the most relevant positions, as indicated by the geologic structure. If the reflector dip is known at the CIP locations, then the computational cost can be reduced by evaluating only two components of the space‐lag vector. The transformation from extended images to angle gathers is a planar Radon transform which depends on the local medium parameters. This transformation allows us to separate all illumination directions for a given experiment, or between different experiments. We do not need to decompose the reconstructed wavefields or to choose the most energetic directions for decomposition. Applications of the method include illumination studies in complex areas where ray‐based methods fail, and assuming that the subsurface illumination is sufficiently dense, the study of amplitude variation with aperture and azimuth angles.  相似文献   

Speciation and geospatial analysis of disinfection byproducts in urban drinking water     

A. Siddique  S. Saied  E. Zahir  Z. A. Nayyer  N. A. Zaigham 《International Journal of Environmental Science and Technology》2014,11(3):739-746

Trihalomethanes (THMs) are the most abundant disinfection byproducts (DBPs) of the chlorination disinfection. THMs speciation and their geospatial distribution were examined in 58 locations throughout the water distribution network of Karachi city. THMs (CHCl₃, CHCl₂Br, CHClBr₂ and CHBr₃) and physico-chemical parameters (pH, TDS, DO, Residual chlorine, temperature and TOC) were determined. CHCl₃ was the major THM found in all water samples of 58 locations, which accounted for 91.69 % of the total THMS followed by CHCl₂Br (5.69 %), CHClBr₂ (1.78 %) and CHBr₃ (0.85 %). Total THMs level exceed the maximum contamination level of WHO and USEPA at some locations. Varying nature of correlation from high to low was found within THMs and among the physico-chemical parameters. GIS linked geospatial analysis revealed the association of THMs level with demographical and geological based variations from east to west of Karachi city. Continuous monitoring program and legislation for the contaminant levels were suggested to avoid adverse public health impact of THMs in drinking water supplies.  相似文献   

Rare Earth and High Field‐Strength Elements in the Multani Mitti Clay: A Study Using INAA     

Shahida Waheed  Naila Siddique  Yasir Faiz 《Geostandards and Geoanalytical Research》2013,37(2):197-205

Instrumental neutron activation analysis was used to determine nine rare earth elements (REE), Sc and five high field‐strength elements (HFSE) in the Multani Mitti (MM) clay. Chondrite‐normalised rare earth element patterns for the MM clay compared with those for the Post‐Archaean Australian Shale (PAAS), Upper Continental Crust (UCC) and North American Shale Composite (NASC) showed enrichment of light REEs and depletion of heavy REEs with a slight negative Eu anomaly. The Multani Mitti clay showed close resemblance to PAAS and NASC in its average REE and HFSE contents. Positive correlations between La/Ce, La/Sm, La/Yb, Zr/Hf, Th/U and Th/Ta ratios predict enrichment of LREEs, Zr and Th and depletion of HREEs. A parent source of felsic origin for the MM clay is also endorsed through the high La/Th and low Th/Sc ratios observed.  相似文献   

A three-step strategy for generalization of 3D building models based on CityGML specifications     

Siddique Ullah Baig  Alias Abdul Rahman 《GeoJournal》2013,78(6):1013-1020

3D building models of the world exhibit multi-scale properties. Different level-of-details (LoDs) are important for different applications. Therefore, generation of multi-scale representation of 3D building models to fulfill the demands of these applications is a generalization problem. In order to generalize 3D buildings, different pieces of information need to be preserved or removed to restrict the amount of data represented on a certain LoD. In this work, a three-step strategy based on simplification, aggregation and reconstruction of generalized buildings represented in City Geography Markup Language (CityGML) is proposed. The minimum length of edges (threshold value) for removal of amount of data is restricted to generalization specifications of CityGML characterized by differing accuracies and minimal dimensions of objects for each LoD. The main part of this paper is simplification of ground plans. For this purpose, a new approach is proposed to restrict number of edges, curves, and corners of ground plan of 3D building model on a certain LoD. Algorithms for simplification with the aim to derive LoD1 from exterior shells of buildings at LoD3 are implemented and tested on a number of buildings of Putrajaya city. The experiments showed that length of edge as threshold value is directly proportional to the size of generalized models.  相似文献   

Mapping spectral tropicality in The Maid and Return to Pontianak   总被引：1，自引：1，他引：0  

Sophia Siddique Harvey 《Singapore journal of tropical geography》2008,29(1):24-33

Contemporary, postcolonial Singapore has tamed, managed, and essentially disavowed its tropicality, aptly captured symbolically as the 'air-conditioned nation'. This essay traces how two recent Singapore horror films, The Maid (2005) and Return to Pontianak (2001), evoke the 'return of the repressed' as a form of haunting that I call 'spectral tropicality'. The films image and imagine this spectral return through unruly bodies (citizen subjects, female domestic workers, ghosts and vampire-ghosts) and uncanny landscapes (the jungle and city). In particular, the films and this analysis examine two sociocultural spectres lurking beneath Singapore as a tropical urban city-nation: the female domestic worker ( The Maid ) and ethnoracial folk beliefs ( The Maid and Return to Pontianak ). The Maid features the Hungry Ghosts Festival in the Chinese religious calendar, ghost marriages and an engagement with yin and yang energies, while Return to Pontianak deals with Malay folk beliefs of semangat ('life force'), and the pontianak, a female vampire-ghost. The Maid attempts to integrate Chinese folk beliefs into contemporary Singapore's cityscape, particularly the architecturally conserved Chinatown shophouses, while Return to Pontianak displaces Malay folk beliefs onto the tropical forest, which is mapped as a threatening other(ed) space and serves as Singapore's tropical doppelganger. Both films suggest that these folk beliefs have an unruly presence within the state's seemingly harmonious and meritocratic ethnoracial ideologies.  相似文献   

Recent Sea Level and Sea Surface Temperature Changes Along the Maldives Coast     

O. P. Singh  Tariq Masood Ali Khan  Fahmida Aktar  Majajul Alam Sarker 《Marine Geodesy》2013,36(4):209-218

Maldives, a South Asian small island nation in the northern part of the Indian Ocean is extremely vulnerable to the impacts of Sea Level Rise (SLR) due to its low altitude from the mean sea level. This artricle attempts to estimate the recent rates of SLR in Maldives during different seasons of the year with the help of existing tidal data recorded in the Maldives coast. Corresponding Sea Surface Temperature (SST) trends, utilizing reliable satellite climatology, have also been obtained. The relationships between the SST and mean sea level have been comprehensively investigated. Results show that recent sea level trends in the Maldives coast are very high. At Male, the capital of the Republic of Maldives, the rising rates of Mean Tidal Level (MTL) are: 8.5, 7.6, and 5.8 mm/year during the postmonsoon (October-December), Premonsoon (March-May) and southwest monsoon (June-September) seasons respectively. At Gan, a station very close to the equator, the increasing rate of MTL is maximum during the period from June to September (which is 6.2 mm/year). These rising trends in MTL along the Maldives coast are certainly alarming for this small developing island nation, which is hardly one meter above the mean sea level. Thus there is a need for careful monitoring of future sea level changes in the Maldives coast. The trends presented are based on the available time-series of MTL for the Maldives coast, which are rather short. These trends need not necessarily reflect the long-term scenario. SST in the Maldives coast has also registered significant increasing trend during the period from June to September. There are large seasonal variations in the SST trends at Gan but SST and MTL trends at Male are consistently increasing during all the seasons and the rising rates are very high. The interannual mode of variation is prominent both in SST as well as MTL. Annual profile of MTL along the Maldives coast is bimodal, having two maxima during April and July. The April Mode is by far the dominant one. The SST appears to be the main factor governing the sea level variations along the Maldives coast. The influence of SST and sea level is more near the equatorial region (i.e., at Gan). There is lag of about two months for the maximum influence of SST on the sea level. The correlation coefficient between the smoothed SST and mean tidal level at Gan with lag of two months is as high as ~ +0.8, which is highly significant. The corresponding correlation coefficients at Male with the lags of one and two months are +0.5 and +0.3, respectively. Thus, the important finding of the present work for the Maldives coast is the dominance of SST factor in sea level variation, especially near the region close to the equator.  相似文献   

Sea Level Changes Along Bangladesh Coast in Relation to the Southern Oscillation Phenomenon   总被引：1，自引：1，他引：0  

O. P. Singh Tariq Masood Ali Khan  Tad S. Murty  Md. Sazedur Rahman 《Marine Geodesy》2013,36(1):65-72

Interannual variations of sea level along the Bangladesh coast are quite pronounced and often dominate the long-term sea level trends that are taking place. The El Niño/Southern Oscillation (ENSO) induced variation is an important component of interannual mode of variations. The present article deals with the relationship between the sea level variations along the Bangladesh coast and the Southern Oscillation phenomenon. The mean tide level data of monsoon season (June to September) pertaining to Hiron Point (in Sundarbans) and Char Changa (on the mouth of Meghna River) have been analyzed and correlated to the Southern Oscillation Index (SOI). The annual variation of mean tide level in the coastal areas of Bangladesh reveals that the tide level reaches its peak during the monsoon season. The maximum tide level during the calendar year is recorded in August. Thus, it is not surprising that the inundation of the coastal belt of Bangladesh due to the floods is most common during the summer monsoon season, especially from July to September. Therefore, the sea level variations during the monsoon are of paramount importance to Bangladesh. The results of the present study show that both at Hiron Point and Char Changa there is a substantial difference between the mean tide level during the El Niño and La Niña monsoons. The mean tide level at Hiron Point is higher by about 5 cm during August of La Niña years as compared to that during the El Niño years. The difference at Char Changa, which is located at the mouth of Meghna River, is much higher. This is probably due to the increased fresh water discharge into the Meghna River during La Niña years. Thus at the time of crossing of a monsoon depression, the chances of widespread inundation are higher during a La Nin~a year as compared to that during an El Niño year. The Correlation Coefficients (CCs) between Mean Tide Levels (MTLs) at Hiron Point and Char Changa and the SOI during September (at the end of monsoon) are +0.33 and +0.39 respectively. These CCs are statistically significant at 90% and 95% levels, respectively. These results may find applications in the preparedness programs for combating sea level associated disasters in Bangladesh.  相似文献   

Heavy metal toxicity levels in the coastal sediments of the Arabian Sea along the urban Karachi (Pakistan) region   总被引：1，自引：0，他引：1  

Azhar Siddique  Majid Mumtaz  Nayyer A. Zaigham  Khalil A. Mallick  Sumayya Saied  Erum Zahir  Haider A. Khwaja 《Marine pollution bulletin》2009,58(9):1406-1414

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Research Note: Full‐waveform inversion of the unwrapped phase of a model     

Tariq Alkhalifah 《Geophysical Prospecting》2014,62(2):397-403

Reflections in seismic data induce serious non‐linearity in the objective function of full‐ waveform inversion. Thus, without a good initial velocity model that can produce reflections within a half cycle of the frequency used in the inversion, convergence to a solution becomes difficult. As a result, we tend to invert for refracted events and damp reflections in data. Reflection induced non‐linearity stems from cycle skipping between the imprint of the true model in observed data and the predicted model in synthesized data. Inverting for the phase of the model allows us to address this problem by avoiding the source of non‐linearity, the phase wrapping phenomena. Most of the information related to the location (or depths) of interfaces is embedded in the phase component of a model, mainly influenced by the background model, while the velocity‐contrast information (responsible for the reflection energy) is mainly embedded in the amplitude component. In combination with unwrapping the phase of data, which mitigates the non‐linearity introduced by the source function, I develop a framework to invert for the unwrapped phase of a model, represented by the instantaneous depth, using the unwrapped phase of the data. The resulting gradient function provides a mechanism to non‐linearly update the velocity model by applying mainly phase shifts to the model. In using the instantaneous depth as a model parameter, we keep track of the model properties unfazed by the wrapping phenomena.  相似文献