Greenhouse warming over Indian sub-continent     

M. Lal  B. Bhaskaran 《Journal of Earth System Science》1992,101(1):13-25

A hierarchy of climate models have been developed and applied to the problem of doubling the CO₂ concentration in the atmosphere. Currently available general circulation models include the most complete treatment of the global wanning and are capable of providing changes in several of the meteorological parameters in time scales of half a century or even more. Much skill is gradually being achieved now for future climate simulations. In this paper, we have attempted to describe the response of the National Center for Atmospheric Research Climate Community Model (NCAR CCM), whose performance for northern hemispheric climate simulations was reported to be very satisfactory to Indian region. The seasonal (winter and summer) changes in surface temperature, rainfall and soil moisture expected over the Indian sub-continent due to doubling of CO₂ in the atmosphere as inferred from model output statistics are discussed. A probable scenario for sea level rise along the Indian coastline by the year 2030 AD as a result of ocean water’s expansion due to global warming is outlined. These projections should not be treated as predictions of what is going to happen over the Indian sub-continent. Rather, they merely illustrate to what extent we might be affected by the future climate change.  相似文献   

Reply to comment of M. Ozima on “An important source of He (and He) in diamonds”     

D. Lal 《Earth and Planetary Science Letters》1990,101(1)

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Post-eruptive sedimentary processes in volcanic crater lakes: implications for deciphering the Samoan sedimentary record     

A. Fepuleai  S. J. Gale  N. A. Wales  S. P. L. McInerney  K. K. Lal  B. V. Alloway 《Journal of Paleolimnology》2018,60(4):473-493

The two largest islands of the Samoan chain, Savai’i and Upolu, possess almost 400 volcanic cones. Their craters form enclosed, internally drained basins that potentially retain long, detailed and uninterrupted sedimentary sequences. Because of the sparsity, fragmentary nature and low temporal resolution of records of environmental change from the tropical Pacific, these deposits have the potential to fill an important gap in our knowledge of global climatic and environmental change. To interpret such records we must understand the depositional processes that operate in these basins. Unfortunately, although the post-eruptive sedimentology of volcanic calderas and maars is relatively well-established, that of crater lakes remains poorly understood. The volcanic edifice of Mount Lanotō in southeast Upolu was selected for investigation. The form of the volcano and its crater are typical of those observed across the island. The sediments retained in the crater are composed largely of plant-organic-rich muds that display little visible evidence of stratigraphic variation. Mineral magnetic and chemical methods were therefore employed to document the types and distribution of sedimentary facies represented in the post-eruptive crater fill and, by inference, the processes of sedimentation that had operated in the crater. The earliest post-eruptive deposits are the result of the failure of the crater’s oversteepened internal slopes. The crater floor subsequently collapsed to form a pit crater. The basal deposits in the pit crater are likely to be the product of the collapse of its walls and roof. However, the bulk of the material in the feature was laid down under lacustrine conditions. These deposits accumulated in a relatively deep-water environment. Across the rest of the accumulation zone, by contrast, water levels appear to have been shallow. Sedimentation during this phase was dominated by autochthonous plant-organic-rich deposits, with minor fine-grained clastic input. Deposition was intermittently interrupted by localised episodes of mass movement that reworked the regolith mantling the steep internal slopes of the crater into the accumulation zone in the form of low-angle fans. At the broad scale, the sedimentology of Lake Lanotō displays similarities with that of volcanic calderas and maar lakes. However, the morphological simplicity of the basin, the general absence of contemporaneous volcanic activity, the timing of the onset of lacustrine conditions, the derivation of the clastic deposits in the volcanic crater almost solely from the by-products of the volcanic eruption, and the high biological activity in the lake waters mean that there are important differences between the types and distribution of sedimentary facies identified in Lake Lanotō and those represented in models of deposition in maars and volcanic calderas.  相似文献   

On the validity of series expansion being used for the position of a point on a Roche equipotential     

A. K. Lal  S. Saini  C. Mohan  V. P. Singh 《Astrophysics and Space Science》2007,310(3-4):317-320

The concept of Roche equipotentials has been frequently used in literature to study the problems of rotating stars and stars in binary systems. However in spite of using this simplifying concept, it is still not possible to express the position of a point in the potential field of such a system in a closed analytic form. In order to carry out further analytic studies, Kopal (Adv. Astron. Astrophys. 9:1–65, 1972), therefore, developed a series expansion for it. The series expansion of Kopal has often been used in the analysis of the problem of equilibrium structure and the periods of oscillations of rotating stars and stars in binary systems, but its validity and convergence has not been analytically established. It is important that this aspect of the problem is checked so that one is sure of the correctness of subsequent analysis and results based on this series expansion. In the present brief note, we have addressed ourselves to this problem and validated the correctness of the numerical results obtained through the use of this series expansion.  相似文献   

A database of phase calibration sources and their radio spectra for the Giant Metrewave Radio Telescope     

Dharam V. Lal  Shilpa S. Dubal  Sachin S. Sherkar 《Experimental Astronomy》2016,42(3):319-341

We are pursuing a project to build a database of phase calibration sources suitable for Giant Metrewave Radio Telescope (GMRT). Here we present the first release of 45 low frequency calibration sources at 235 MHz and 610 MHz. These calibration sources are broadly divided into quasars, radio galaxies and unidentified sources. We provide their flux densities, models for calibration sources, (u,v) plots, final deconvolved restored maps and clean-component lists/files for use in the Astronomical Image Processing System (aips) and the Common Astronomy Software Applications (casa). We also assign a quality factor to each of the calibration sources. These data products are made available online through the GMRT observatory website. In addition we find that (i) these 45 low frequency calibration sources are uniformly distributed in the sky and future efforts to increase the size of the database should populate the sky further, (ii) spectra of these calibration sources are about equally divided between straight, curved and complex shapes, (iii) quasars tend to exhibit flatter radio spectra as compared to the radio galaxies or the unidentified sources, (iv) quasars are also known to be radio variable and hence possibly show complex spectra more frequently, and (v) radio galaxies tend to have steeper spectra, which are possibly due to the large redshifts of distant galaxies causing the shift of spectrum to lower frequencies.  相似文献   

Equilibrium Structure of Rotationally and Tidally Distorted Prasad Model Including the Effect of Mass Variation Inside the Star     

Seema Saini  A. K. Lal  Sunil Kumar 《Astrophysics》2014,57(1):119-129

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Near-surface study of a hot spring site in Fiji     

Alvin Lal  Ravin N. Deo  Ajal Kumar 《Acta Geophysica》2018,66(4):659-672

A geophysical investigation of a hot spring system located in Rabulu, Fiji, was carried out from October 2014 to March 2015. The investigation covered a survey area of 6075 m². Self-potential (SP), ground temperature and soil carbon dioxide (CO₂) concentrations were measured and investigated for their distribution characteristics and inter-linkages. Results indicated obvious anomalous zone at the hot spring discharge site. The SP profile analysis highlighted thermal water upwelling zones and elevation-driven subsurface groundwater pathways. Measurement of subsurface temperatures up to 1 m depths revealed increasing temperatures, indicating potentially high thermal gradients in the area. Surface soil CO₂ distributions also agreed with SP and ground temperature results. The overall result of the study demonstrated that synchronised measurements of SP, ground temperature and soil CO₂ can be instrumental in identifying anomalous zones near the hot spring sites. Other parameters such as spring water temperature, discharge rate and energy flux estimates from the spring were calculated and analysed. The high-dense multi-parameter data coverage allowed interpretation of geothermal features at a scale never conducted in Fiji before. The near-surface investigations reported in this study corroborate previously suggested steady geothermal activity in the region, deserving further detailed investigation.  相似文献   

Plant species diversity along an altitudinal gradient of Bhabha Valley in western Himalaya   总被引：1，自引：1，他引：0  

Amit Chawla  S. Rajkumar  K. N. Singh  Brij Lal  R. D. Singh  A. K. Thukral 《山地科学学报》2008,5(2):157-177

The present study highlights the rich species diversity of higher plants in the Bhabha Valley of western Himalaya in India. The analysis of species diversity revealed that a total of 313 species of higher plants inhabit the valley with a characteristic of moist alpine shrub vegetation. The herbaceous life forms dominate and increase with increasing altitude. The major representations are from the families Asteraceae, Rosaceae, Lamiaceae and Poaceae, suggesting thereby the alpine meadow nature of the study area. The effect of altitude on species diversity displays a hump-shaped curve which may be attributed to increase in habitat diversity at the median ranges and relatively less habitat diversity at higher altitudes. The anthropogenic pressure at lower altitudes results in low plant diversity towards the bottom of the valley with most of the species being exotic in nature. Though the plant diversity is less at higher altitudinal ranges, the uniqueness is relatively high with high species replacement rates. More than 90 % of variability in the species diversity could be explained using appropriate quantitative and statistical analysis along the altitudinal gradient. The valley harbours 18 threatened and 41 endemic species, most of which occur at higher altitudinal gradients due to habitat specificity.  相似文献   

怒江峡谷构造地貌的演化:阶地宇宙成因核素定年的初步结果   总被引：12，自引：5，他引：7       下载免费PDF全文

顾兆炎  许冰  吕延武  A.Aldahan  D.Lal 《第四纪研究》2006,26(2):293-294

地貌产生于构造活动和各种地表营力驱动的侵蚀夷平和堆积过程,如在构造抬升活跃的地区,河流强烈的侵蚀作用往往造就深切的峡谷地貌。对于这样的地区河流下切速率往往被用来衡量构造抬升速率[1,2]。然而河流下切速率的变化不仅与构造抬升有关,而且与气候变化有关。因此,正确理解  相似文献   

Some aspects of the geochemistry of silicon isotopes     

D. Lal  B.L.K. Somayajulu 《Tectonophysics》1984,105(1-4)

The applications of the isotopes of the abundant element silicon as a tracer in the study of the earth sciences are discussed. The relatively long-lived radionuclide of silicon, ³²Si, finds important applications as a tracer for studying aqueous geochemistry, biogeochemical cycles of silicon in the oceans, and the chronology of glaciers and biogenic silica-rich sediments in lacustrine and marine environments.It is pointed out that a simultaneous study of ¹⁶O and ³⁰Si in exotic phases frequently found in carbonaceous chondrites should be useful for delineating nucleosynthetic effects distinctly from isotopic effects due to chemical fractionation.  相似文献