Sea Level Variations Associated with Upwelling/ Downwelling Along the West Coast of India     

A. D. Rao  S. V. Babu  Madhu Sharma 《Marine Geodesy》2013,36(3):153-170

A three-dimensional numerical model is developed and used to study the coastal upwelling processes and corresponding seasonal changes in the sea level along the west coast of India. The upwelling and associated sea level variations are seen as a response of coastal ocean to pure wind stress forcing. The model is designed to represent coastal ocean physics by resolving surface and bottom Ekman layers as realistically as possible. The prognostic variables are the three components of the velocity field, temperature, salinity and turbulent energy. The governing equations together with their boundary conditions are solved by finite-difference techniques. Experiments are performed to investigate sea level fluctuations associated with the thermal response and alongshore currents of the coastal waters. The model is forced with mean monthly wind stress forcing of January, May, July and September representing northeast monsoon and different phases of the southwest monsoon. It is known from the observational study that the upwelling process reaches to the surface waters by May along the coastal waters of the extreme southwest peninsular region. The process is more intense in July compared to May and September and its strength decreases from south to north. However, during the northeast monsoon season, which is represented by January wind stress forcing in the model, downwelling is simulated along the coast. The model simulations of the coastal response are compared with the observations and are found to be in good agreement. The maximum computed vertical velocity of about 2.0 2 10 -3 cm s -1 is predicted in July in the southern region off the coast.  相似文献   

Revision of Handbook of Hydrogeology (2nd Edition)          下载免费PDF全文

Tong Yuanqing  Liu Li  Wang? Xiuming  Li Yingzhi 《地下水科学与工程》2013,1(2):41-47

Handbook of Hydrogeology is a professional reference book guiding the work and re-search of hydrogeology and providing enlightenment to hydrogeologists and those working in re-lated fields. This paper introduces the revision and enlargement of Handbook of Hydro-geology (2nd edition) on the basis of its first edition. It gives a brief account of the background, principles, and necessity of revising the handbook. The content, features and application of the handbook are also addressed.  相似文献   

Ensemble-Based Observation Targeting for Improving Ozone Prediction in Houston and the Surrounding Area     

Naifang?Bei  Fuqing?ZhangEmail author  John?W.?Nielsen-Gammon 《Pure and Applied Geophysics》2012,169(3):539-554

This study examines the effectiveness of targeted meteorological observations for improving ozone prediction in Houston and the surrounding area based on perfect-model simulation experiments. Supplementary observations are targeted for the location that has the highest impact factor (maximum Kalman gain) estimated from an ensemble and is expected to minimize ozone forecast uncertainty at the verification time. It is found that the observational impact factor field varies with time and is sensitive to ensemble resolutions and physics parameterizations. The efficiency of observation targeting is further examined through assimilating observations in areas with different impact factors using an ensemble Kalman filter. It is found that the ensemble sensitivity analysis is capable of locating supplementary observations that may reduce meteorological and ozone forecast error, but not as effectively as expected.  相似文献   

Data Assimilation and its Applications     

Maithili?SharanEmail author  Jean?Pierre?Issartel 《Pure and Applied Geophysics》2012,169(3):309-310

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Dead Sea Basin Imaged by Ambient Seismic Noise Tomography     

Jacek?StankiewiczEmail author  Michael?H.?Weber  Ayman?Mohsen  Rami?Hofstetter 《Pure and Applied Geophysics》2012,169(4):615-623

In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007 to be used for ambient seismic noise analysis. Empirical Green’s functions are extracted from cross-correlations of long term recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green’s functions makes it possible to identify the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth of ~5 km. The reliability of the results is confirmed by checkerboard recovery tests.  相似文献   

The Effects of the Earth’s Curvature on Gravity and Geoid Calculations   总被引：1，自引：0，他引：1  

Hasan??av?akEmail author 《Pure and Applied Geophysics》2012,169(4):733-740

While it is obvious that large-scale gravity studies should account for the sphericity of the Earth, each case should be examined. If a geometry model is very large for the 3D-gravity calculation, it cannot be correctly defined in Cartesian coordinates. Because of the Earth’s curvature it is necessary to use spherical coordinates, the importance of which is shown in this paper. The calculation of the gravity for a cylinder reveals, 1 m above the center of the cylinder, a relative difference of 13% between the models with Cartesian and spherical coordinates.  相似文献   

Homogenization of Earthquake Catalog for Northeast India and Adjoining Region   总被引：1，自引：0，他引：1  

Ranjit?DasEmail author  H.?R.?Wason  M.?L.?Sharma 《Pure and Applied Geophysics》2012,169(4):725-731

A catalog for northeast India and the adjoining region for the period 1897–2009 with 4,497 earthquakes events is compiled for homogenization to moment magnitude M _w,GCMT in the magnitude range 3–8.7. Relations for conversion of m _b and M _s magnitudes to M _w,GCMT are derived using three different methods, namely, linear standard regression, inverted standard regression (ISR) and orthogonal standard regression (OSR), for different magnitude ranges based on events data for the catalog period 1976–2006. The OSR relations for M _s to M _w,GCMT conversion derived in this paper have significantly lower errors in regression parameters compared to the relations reported in other studies. Since the number of events with magnitude ≥7 for this region is scanty, we, therefore, considered whole India region to obtain the regression relationships between M _w,GCMT and M _s,ISC. A relationship between M _w,GCMT and M _w,NEIC is also obtained based on 17 events for the range 5.2 ≤ magnitude ≤ 6.6. A unified homogeneous catalog prepared using the conversion relations derived in this paper can serve as a reference catalog for seismic hazard assessment studies in northeast India and the adjoining region.  相似文献   

Joint inversion of teleseismic P waveforms and surface-wave group velocities from ambient seismic noise in the Bohemian Massif     

Bohuslav R??ek  Jaroslava Plomerová  Vladislav Babu?ka 《Studia Geophysica et Geodaetica》2012,56(1):107-140

Joint inversion of teleseismic P-waveforms and local group velocities of surface waves retrieved from ambient seismic noise has been performed to model velocity structure of the crust and uppermost mantle of the Bohemian Massif. We analysed P-waveforms of 381 teleseismic earthquakes recorded at 54 broadband seismic stations located on the territory of the Czech Republic and in its close surroundings. Group velocities of Rayleigh and Love surface waves were obtained by cross-correlating long-term recordings of seismic noise. The basis for waveform inversion is the well-known methodology of P-to-S receiver functions constructed from converted phases. Due to instabilities in direct inversion of receiver functions caused by the necessity of applying deconvolution, we propose an alternative formulation to fit observed and calculated radial components of P waveforms. The joint inversion is transformed into a search for the minimum of the cost function defined as a weighted sum of waveform and group velocity misfits. With the use of the robust stochastic optimizer (Differential Evolution Algorithm), neither derivatives nor a starting model are needed. The task was solved for 1D layered isotropic models of the crust and the uppermost mantle. We have performed a sequence of inversions with models containing one, two, three and four layers above a half-space. By using statistical criteria (F-test) we were able to select the simplest velocity models satisfying data and representing local geological structures. Complex crustal models are typical for stations located close to boundaries of major tectonic units. The relatively low average P to S wave-velocity ratio is in agreement with the generally accepted view that the BM crust is predominantly felsic.  相似文献   

Comparison of the FORT approximation of the coupling ray theory with the Fourier pseudospectral method     

Ivan P?en?ík  Véronique Farra  Ekkehart Tessmer 《Studia Geophysica et Geodaetica》2012,56(1):35-64

The standard ray theory (RT) for inhomogeneous anisotropic media does not work properly or even fails when applied to S-wave propagation in inhomogeneous weakly anisotropic media or in the vicinity of shear-wave singularities. In both cases, the two shear waves propagate with similar phase velocities. The coupling ray theory was proposed to avoid this problem. In it, amplitudes of the two S waves are computed by solving two coupled, frequency-dependent differential equations along a common S-wave ray. In this paper, we test the recently developed approximation of coupling ray theory (CRT) based on the common S-wave rays obtained by first-order ray tracing (FORT). As a reference, we use the Fourier pseudospectral method (FM), which does not suffer from the limitations of the ray method and yields very accurate results. We study the behaviour of shear waves in weakly anisotropic media as well as in the vicinity of intersection, kiss or conical singularities. By comparing CRT and RT results with results of the FM, we demonstrate the clear superiority of CRT over RT in the mentioned regions as well as the dangers of using RT there.  相似文献   

Sea level variability at Antalya and Mente? tide gauges in Turkey: atmospheric, steric and land motion contributions     

Mehmet Simav  Hasan Yildiz  Ali Türkezer  Onur Lenk  Emin ?zsoy 《Studia Geophysica et Geodaetica》2012,56(1):215-230

Sea level trends and interannual variability at Antalya and Menteş tide gauges are investigated during the 1985–2001 period, quantifying the roles of atmospheric, steric and local land motion contributions. Tide gauge sea level measurements, temperature/salinity climatologies and GPS data are used in the analyses and the results are compared with the output of a barotropic model forced by atmospheric pressure and wind. The overall sea level trends at two tide gauges collocated with GPS are in the range of 5.5 to 7.9 mm/yr during the study period, but showing different behaviour in the sub-periods 1985–1993 and 1993–2001 due to variations in the contributing factors both in space and time. After the removal of the atmospheric forcing and steric contribution from sea level records, the resulting trends vary between 1.9 to 4.5 mm/yr in Antalya and −1.2 to −11.6 mm/yr in Menteş depending on the period considered. Vertical land movement estimated from GPS data seems to explain the high positive residual trend in Antalya during the whole period. On the other hand, the source of the highly negative sea level trend of about −14 mm/yr in Menteş during 1985–1993 could not be resolved with the available datasets. Interannual variability of wind and atmospheric pressure appear to dominate the sea level at both tide gauges during the study period. Atmospheric and steric contributions together account for ∼50% of the total sea level variance at interannual time scales. Mass induced sea level variations which were not considered in this study may help to close the sea level trend budgets as well as to better explain the interannual sea level variance.  相似文献