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1.
Based on shipboard and satellite observations, the characteristics of upwelling in Lake Baikal in the period of direct temperature stratification have been determined for the first time. Coastal upwellings appear annually under the effect of run-down and alongshore winds and are traced along the coast to a distance of up to 60–100 km and up to 250 km in North Baikal. Analogous to the way it occurs in seas, water rises from the depths of 100–200 m (350 m as a maximum) at the velocity of 0.1 × 10−2−6.5 × 10−2 cm/s. Divergence in the field of intràbasin cyclonic macrovortices produces upwelling in the Baikal pelagic zone and downwelling in the vicinity of shores; this lasts from 7 to 88 days and covers the depth interval of 80–300 m in August and up to 400–800 m in early-mid November. The area of upwellings occupies up to 20–60% of the separate basins of the lake. Vertical circulation of water in the field of pelagic upwellings leads to intensification of coastal currents and to formation of the thermobar with a heat inert zone in the central part of the lake in November, and this thermobar is not observed in other lakes, at that.  相似文献   

2.
Measurements of intensities at two fixed wavelengths in the OH (7-2) band were carried out at Mt Abu (24.6° N, 76.7° E) from 1973–76 to estimate neutral temperature in the region of 80–90 km altitude. It was observed that on some nights the temperature in this region shows periodic oscillations throughout the night. It was found from statistical analysis that the periods of these fluctuations are comparable to the theoretically predicted periods of internal gravity waves. If the periodic temperature variations observed in this region are attributed to the influence of gravity waves, according to the Hines theory only the magnitude of the horizontal component of wave-induced wind velocity can be computed. Using the measured relative temperature fluctuations it is found that the magnitude is 15–30 m/sec.  相似文献   

3.
Preliminary analysis of seismograms recorded by a wide band high dynamic range digital seismograph installed under a collaborative research programme between IPG, Paris and NGRI, Hyderabad, indicates that the crust and upper mantle structure below the Indian continent are characterized by high velocity up to a depth of 500 km. Both the group and phase velocities in the period range of 100–350s are found to be faster by 3–4% and 1–3% respectively compared with global models such as the preliminary reference earth model.  相似文献   

4.
Characteristics of aerosols in the Atmospheric Boundary Layer (ABL) obtained from a bistatic CW lidar at Trivandrum for the last one decade are used to investigate the role of ABL micro-meteorological processes in controlling the altitude distribution and size spectrum. The altitude structure of number density shows three distinct zones depending on the prevailing boundary layer feature; viz, the well-mixed region, entertainment region and upper mixing region. In the lower altitudes vertical mixing is very strong (the well-mixed region) the upper limit of which is defined as aerosol-mixing height, is closely associated with the low level inversion. The aerosol mixing height generally lies in the range 150 to 400 m showing a strong dependence on the vertical eddy mixing processes in ABL. Above this altitude, the number density decreases almost exponentially with increase in altitude with a scale height of 0.5–1.5 km. The aerosol mixing height is closely associated with the height of the Thermal Internal Boundary Layer (TIBL). Sea-spray aerosols generated as a result of the interaction of surface wind with sea surface forms an important component of mixing region aerosols at this location. This component shows a non-linear dependence on wind speed. On an average, depending on the season, the mixing region contributes about 10–30% of the columnar aerosol optical depth (AOD) at 0.5Μm wavelength. A long term increasing trend (∼ 2.8% per year) is observed in mixing region AOD from 1989 to 1997. A study on the development of the aerosols in the nocturnal mixing region shows that the convectively driven daytime altitude structure continues to persist for about 4–5 hrs. after the sunset and thereafter the altitude structure is governed by vertical structure of horizontal wind. Stratified aerosol layers associated with stratified turbulence is very common during the late night hours.  相似文献   

5.
The deep crustal structure of eastern Dharwar craton has been investigated through τ-p extremal inversion of P-wave travel times from a network of seismographs recording quarry blasts. Travel times have been observed in the distance range 30–250 km in a laterally homogeneous lithospheric segment Main features of the inferred velocity-depth relationship include: (a) 29 km thick combined upper and middle crust velocity varying from 6 km/s to 7 km/s, with no observable velocity discontinuity in this depth range; (b) a lower crust (∼ 29–41 km) with velocity increasing from 7.0 to 7.3 km/s; (c) an average upper mantle velocity of 8.1 km/s; and (d) presence of a 12 km thick high velocity crustal layer (7.4 – 7.8 km/s) in the depth range 41–53 km, with a distinct velocity gradient marking a velocity increase of 0.4 km/s. The anomalous 53 km thick crust is viewed as a consequence of magmatic underplating at the base of the crust in the process of cratonization of the eastern Dharwar craton during late Archaean. The underplated material reflects here with the velocity of 7–3 to 7–8 km/s below the depth of 40 km. Our proposition of magmatic underplating is also supported by the presence of large scale I-granitoid, a product of partial melting of the upper mantle material.  相似文献   

6.
Applying the method of ‘statistical linear regression’, atomspheric water vapour over oceanic areas has been estimated from the 19GHz and 22 GHz data of the satellite microwave radiometer (SAMIR) system onboard the Bhaskara II satellite. In the absence of any simultaneousin situ measurements on water vapour over ocean, theSAMIR-derived water vapour data have been compared with like data from theNOAA-7 satellite. It is suggested that a positive bias seen in theSAMIR data could be due to calibration errors in the basic data. In view of the observed bias, the original regression equation is modified and then used to obtain water vapour distributions over ocean for winter and south-west monsoon seasons usingSAMIR data of several orbits.  相似文献   

7.
In this paper, acoustic sounder (sodar) derived vertical velocity variance (σ w 2 ) and inversion height (Z i) are used to compute the surface heat flux during the convective activity in the morning hours. The surface heat flux computed by these methods is found to be of the same order of magnitude as that obtained from tower measurements. Inversion heights derived from sodar reflectivity profiles averaged for an hour are compared with those obtained from the σ w 2 /Z profile. Variation of σ w 2 in the mixed layer is discussed. The data were collected during the Monsoon Trough Boundary Layer Experiment 1990 at Kharagpur. The analysis is made for four days which represent the pre-monsoon, onset, active and relatively weak phases of the summer monsoon 1990. The interaction of the ABL with the monsoon activity is studied in terms of the variation of inversion height, vertical velocity variance and surface heat flux as monsoon progresses from June to August.  相似文献   

8.
Threshold velocity for wind erosion: the effects of porous fences   总被引：3，自引：0，他引：3  
Porous fence is a kind of artificial windbreak that has many practical applications. The threshold wind velocities at different distances downwind from porous fences were measured and the corresponding characteristics of particle movement observed to assess their shelter effect. It is found that the fence’s porosity is the key factor that determines the resulting shelter effect. The area near a fence can be typically classified into five regions, each with a different mode of particle movement. Dense fences, and especially solid fences, favor the accumulation of sand upwind of the fences. Fences with porosities of 0.3–0.4 produce the maximum threshold wind velocity; those with porosities of 0.3–0.6 (depending on the fence height) provide the maximum effective shelter distance. It is confirmed that the fence porosities of 0.3–0.4 that have been proposed for practical application in previous research are the most effective for abating wind erosion.  相似文献   

9.
Nine vertical electrical soundings of Schlumberger configuration were measured with AB/2 = 1–500 m. Manual and computerized interpretation were done to detect the subsurface stratigraphy of the study area. The results show that the subsurface section consists of alternated units of limestone, clay, marly limestone and dolomitic limestone and the thickness of clay unit ranged from 10 to 40 m. Nine dipole–dipole sections have also been constructed to give a clearer picture of the subsurface at the study area. The length of each dipole–dipole section is 235 m, with a electrode spacing ranging between 5 and 25 m. The Res2Dinv software was used for processing and interpretation of field data. The dipole–dipole sections at the upper plateau display high resistivity values at most parts of the plateau. Twelve shallow seismic refraction profiles are measured at selected locations for the dipole sections to define the interface between the fractured limestone and the upper surface of the clay layer. Each profile consists of 24 geophones with a geophone spacing of 2–3 m. Interpretation of seismic data indicates that the surface layer of the upper plateau consists of fractured limestone with a velocity range of 1.16–1.56 km/s and another layer of compacted clay with a velocity range of 1.38–1.88 km/s. Furthermore, the surface layer of the middle plateau consists of marl and marly limestone with a velocity about 2.1 km/s and its underlying layer consists of massive limestone with a velocity of 4.94 km/s.  相似文献   

10.
Few strong relationships exist along the Chesapeake Bay shoreline between the historic erosion rate and the distribution of any of several coastal parameters which were defined and tested using traditional regression and discriminant analysis procedures To develop a simple predictive equation for shore erosion that could be used by coastal managers, the entire Chesapeake Bay shoreline was partitioned into naturally occurring reaches 2–5 km in length, and the historic erosion rate on each reach was modelled as a function of five variables (a) shoreline type, (b) “100-year” storm surge height, (c) mean tide range, (d) wave climate, and (e) potential littoral drift rate The statistical analysis yielded a multiple correlation coefficient (r 2) of 30 8%, discriminant analysis showed only the first two variables listed above are useful predictors (i e, statistically significant) of historic erosion rates A 95-mile portion of the same bay shoreline in Queen Anne’s and Talbot counties was then partitioned into shorter reach lengths (1/2–2km) and more variables were included The multiple correlation coefficient (r 2) improved slightly to 32 9%, but only shoreline type and potential littoral drift rate were found to be useful predictors of historic erosion rates Curiously, the ability to model statistically the historic shore erosion rate is best on those reaches already substantially protected by structures For Queen Anne’s and Talbot counties, the multiple regression coefficient improved to 61 5% when only reaches 1/2–2km in length protected by structures were considered.  相似文献   

11.
Internal Wave (IW) characteristics and the impact of IW on acoustic field have been studied utilizing the hourly time series of temperature and salinity data collected at a coastal site off Paradeep (north Bay of Bengal) during 24–25 October 2008. The IW characteristics, viz. period (t per ), velocity (C vel ), wavelength (L), and wave numbers (k), are found to be 2.133–34.72 h, 0.135 km h−1, 0.37–6.2 km and 2.70–0.16 cycles km−1, respectively. The semi-diurnal tidal forces are predominant than diurnal as well as at other frequencies and its contribution is about 64% towards the total potential energy (E 0 = 3.34 J m−2). Sound velocity perturbations with space and time in the presence of IW field are examined from Garrettt-Munk (GM) model. Transmission loss anomaly for optimized source-receiver configuration at the depth of 53 m and range of 9 km has been computed from acoustic modelling. The loss in the acoustic transmission is found to be 38.4 dB in the presence of low-frequency IW field.  相似文献   

12.
 The empirical linear relation between volume and logarithm of bulk modulus of a material, discovered by Grover, Getting and Kennedy is taken as the basis for our equation of state. Using the latest experimental information on the adiabatic bulk modulus, the equation of state is applied to the three polymorphs of Mg2SiO4 to develop a consistent dataset of their thermodynamic properties in the temperature range of 200–2273 K and a pressure range of 0.1 MPa–30 GPa. The results imply that the bulk sound velocity contrast (v β−v α)/v α increases with temperature along the α–β phase boundary and reaches the value 8.9% at 13.5 GPa, a pressure equivalent to 410 km depth in the Earth. The bulk sound velocity contrast (v γ−v β)/v β decreases with temperature along the β–γ phase boundary and becomes less than 0.7% at temperatures and pressures equivalent to those associated with the 520-km seismic discontinuity in the Earth. Received: 1 August 2000 / Accepted: 1 March 2001  相似文献   

13.
根据体波层析成像技术,利用大量走时数据,做出0°～180°E,30°S～90°S范围内0～2889km深的三维速度分布图像,得到欧亚地区局部区域岩石圈及地幔的高分辨率速度结构,并从地球动力学角度出发对这些成像结果做进一步解释。  相似文献   

14.
Pn velocity has been computed across the NE India and Moho geometry constrained, using regional earthquake travel times recorded by a network of 30 seismological stations operated during February-May 1993. Using an appropriate velocity model and the arrival times at the network stations, preliminary hypocentres of 16 regional earthquakes provided by NEIC were also improved. The average Pn wave velocity in NE India has been found to be 8.5 ±0.2 km/s. It varies from 8.3 to 8.5 km/s beneath the Shillong Plateau, Mikhir hills and Assam valley, which is significantly higher than those in other parts of India. The crustal thickness in NE India is also high, varying from 45–49 km under the Shillong plateau and the adjoining region to 55–65 km in the convergence zone. The presence of a thick crust and high Pn velocity suggests that the lithosphere in NE India is colder, as also indicated by the observed deeper level (45-51 km) seismicity of the region.  相似文献   

15.
Starting from nonhydrostatic Boussinesq approximation equations, a general method is introduced to deduce the dispersion relationships. A comparative investigation is performed on inertia-gravity wave with horizontal lengths of 100, 10 and 1 km. These are examined using the second-order central difference scheme and the fourth-order compact difference scheme on vertical grids that are currently available from the perspectives of frequency, horizontal and vertical component of group velocity. These findings are compared to analytical solutions. The obtained results suggest that whether for the second-order central difference scheme or for the fourth-order compact difference scheme, Charny–Phillips and Lorenz (L) grids are suitable for studying waves at the above-mentioned horizontal scales; the Lorenz time-staggered and Charny–Phillips time staggered (CPTS) grids are applicable only to the horizontal scales of less than 10 km, and N grid (unstaggered grid) is unsuitable for simulating waves at any horizontal scale. Furthermore, by using fourth-order compact difference scheme with higher difference precision, the errors of frequency and group velocity in horizontal and vertical directions produced on all vertical grids in describing the waves with horizontal lengths of 1, 10 and 100 km cannot inevitably be decreased. So in developing a numerical model, the higher-order finite difference scheme, like fourth-order compact difference scheme, should be avoided as much as possible, typically on L and CPTS grids, since it will not only take many efforts to design program but also make the calculated group velocity in horizontal and vertical directions even worse in accuracy.  相似文献   

16.
Analysis of teleseismicP-wave residuals observed at 15 seismograph stations operated in the Deccan volcanic province (DVP) in west central India points to the existence of a large, deep anomalous region in the upper mantle where the velocity is a few per cent higher than in the surrounding region. The seismic stations were operated in three deployments together with a reference station on precambrian granite at Hyderabad and another common station at Poona. The first group of stations lay along a west-northwesterly profile from Hyderabad through Poona to Bhatsa. The second group roughly formed an L-shaped profile from Poona to Hyderabad through Dharwar and Hospet. The third group of stations lay along a northwesterly profile from Hyderabad to Dhule through Aurangabad and Latur. Relative residuals computed with respect to Hyderabad at all the stations showed two basic features: a large almost linear variation from approximately +1s for teleseisms from the north to—1s for those from the southeast at the western stations, and persistance of the pattern with diminishing magnitudes towards the east. Preliminary ray-plotting and three-dimensional inversion of theP-wave residual data delineate the presence of a 600 km long approximately N−S trending anomalous region of high velocity (1–4% contrast) from a depth of about 100 km in the upper mantle encompassing almost the whole width of the DVP. Inversion ofP-wave relative residuals reveal the existence of two prominent features beneath the DVP. The first is a thick high velocity zone (1–4% faster) extending from a depth of about 100 km directly beneath most of the DVP. The second feature is a prominent low velocity region which coincides with the westernmost part of the DVP. A possible explanation for the observed coherent high velocity anomaly is that it forms the root of the lithosphere which coherently translates with the continents during plate motions, an architecture characteristic of precambrian shields. The low velocity zone appears to be related to the rift systems (anomaly 28, 65 Ma) which provided the channel for the outpouring of Deccan basalts at the close of the Cretaceous period.  相似文献   

17.
New data on the deep structure of the White Sea have been obtained. An interpretation of traverses 510 km in total length is presented. It has been found that the area of the Black Sea that was surveyed with the traverses is characterized by a consolidated crust consisting of two layers. In the velocity sections, interleaving of horsts and grabens is sharply identified. In the central part of the sea, an isometric trough is found with sediments up to 7–8 km thick. The trough is surrounded by east- and northeast-striking ledges and faults. Rocks with anomalously increased velocities are found in the lower part of the sedimentary cover. The thickness of the upper crust is 5–7 km. The lower crust is of a complicated structure and is 30 km thick; it forms a large fold surrounded by rocks with decreased velocitys.  相似文献   

18.
The cause for prolific seismicity in the Koyna region is a geological enigma. Attempts have been made to link occurrence of these earthquakes with tectonic strain as well as the nearby reservoirs. With a view to providing reliable seismological database for studying the earth structure and the earthquake process in the Koyna region, a state of the art digital seismic network was deployed for twenty months during 1996–97. We present preliminary results from this experiment covering an area of 60 × 80 km2 with twenty seismic stations. Hypocentral locations of more than 400 earthquakes confined to 11×25 km2 reveal fragmentation in the seismicity pattern — a NE — SW segment has a dip towards NW at approximately 45°, whilst the other two segments show a near vertical trend. These seismic segments have a close linkage with the Western Ghat escarpment and the Warna fault. Ninety per cent of the seismicity is confined within the depth range of 3–10 km. The depth distribution of earthquakes delimits the seismogenic zone with its base at 10 km indicating a transition from an unstable to stable frictional sliding regime. The lack of shallow seismicity between 0 and 3 km indicates a mature fault system with well-developed gouge zones, which inhibit shallow earthquake nucleation. Local earthquake travel time inversion for P- and S-waves show ≈ 2% higher velocity in the seismogenic crust (0–10 km) beneath the epicentral tract relative to a lower velocity (2–3%) in the adjoining region. The high P- and S-wave velocity in the seismogenic crust argues against the presence of high pressure fluid zones and suggests its possible linkage with denser lithology. The zone of high velocity has been traced to deeper depths (≈ 70 km) through teleseismic tomography. The results reveal segmented and matured seismogenic fault systems in the Koyna region where seismicity is possibly controlled by strain build up due to competent lithology in the seismic zone with a deep crustal root.  相似文献   

19.
Broadband receiver functions abstracted from teleseismicP waveforms recorded by a 3-component Streckeisen seismograph at Hyderabad, have been inverted to constrain the shear velocity structure of the underlying crust. Receiver functions obtained from the Hyderabad records of both shallow and intermediate focus earthquakes lying in different station-event azimuths, show a remarkable coherence in arrival times and shapes of the significant shear wave phases:Ps, PpPs, PsPs/PpSs, indicating horizontal stratification within the limits of resolution. This is also supported by the relatively small observed amplitudes of the tangential component receiver functions which are less than 10% of the corresponding radial component. Results of several hundred inversions of stacked receiver functions from closely clustered events (within 2°), show that the crust beneath the Hyderabad granites has a thickness of 36 ± 1 km, consisting of a 10 km thick top layer in which shear wave velocity is 3.54 ± 0.07 km/sec, underlain by a 26 ± 1 km thick lower crust in which the shear wave velocity varies uniformly with a small gradient of 0.02 km/sec/km. The shear wave velocity at its base is 4.1 ± 0.05 km/sec, just above the moho transition zone which is constrained to be less than 4 km thick, overlying a 4.74 ±0.1 km/sec half space.  相似文献   

20.
The Hamamboğazi spa in western Turkey was built around natural hot springs with discharge temperatures in the range of 30–54°C; the waters have near neutral pH values of 6.50–7.10 and a TDS content between 2,694 and 2,982 mg/l. Thermal water with a temperature of 47.5–73°C has been produced at 325 l/s from five wells since 1994, causing some springs to go dry. A management plan is required in the study area to maximize the benefits of this resource, for which currently proposed direct uses include heating in the district and greenhouses, as well as balneology in new spas in the area. The best use for the water from each spring or well will depend on its temperature, chemistry and location. The thermal waters are mixed Na–Mg–HCO3–SO4 fluids that contain a significant amount of CO2 gas. The chemical geothermometers applied to the Hamamboğazi thermal waters yield a maximum reservoir temperature of 130°C. Isotope results (18O, 2H, 3H) indicate that the thermal waters have a meteoric origin: rainwater percolates downward along fractures and faults, is heated at depth, and then rises to the surface along fractures and faults that act as a hydrothermal conduit. The basement around the Banaz Hamamboğazi resort is comprised of Paleozoic metamorphic schist and marbles exposed 8 km south and 15 km north of Banaz. Mesozoic marble, limestone and ophiolitic complex are observed a few km west and in the northern part of Banaz. These units were cut at a depth of 350–480 m in boreholes drilled in the area. Overlying lacustrine deposits are composed of fine clastic units that alternate with gypsum, tuff and tuffites of 200–350 m thickness. The marble and limestones form the thermal water aquifer, while lacustrine deposits form the impermeable cap.  相似文献   

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