Estimation of Sea Ice Thickness from SARAL/AltiKa in Drifting Orbit Phase     

Purvee Joshi  Sandip R. Oza  Ujjwal K. Gupta  Shailendra Saini  D. Ram Rajak  I. M. Bahuguna 《Marine Geodesy》2020,43(3):302-323

Abstract

Intra and inter-annual variations in the sea ice thickness are highly sensitive indicators of climatic variations undergoing in the earth’s atmosphere and oceans. This paper describes the method of estimating sea ice thickness using radar waveforms data acquired by SARAL/Altika mission during its drifting orbit phase from July 2016 onwards yielding spatially dense data coverage. Based on statistical analysis of return echoes, classification of the surface has been carried out in three different types, viz. floe, lead and mixed. Time delay correction methods were suitably selected and implemented to make corrections in altimetric range measurements and thereby freeboard. By assuming hydrostatic equilibrium, freeboard data were converted into sea ice thickness. Results show that sea ice thickness varies from 4 to 5?m near ice shelves and 1 to 2.5?m in the marginal sea ice regions. Freeboard and sea ice thickness estimates were also validated using NASA’s Operation Ice Bridge (OIB) datasets. Freeboard measurements show very high correlation (0.97) having RMSE of 0.13. Overestimation of approximately 1–2?m observed in the sea ice thickness, which could be attributed to distance between AltiKa footprint and OIB locations. Moreover, sensitivity analysis shows that snow depth and snow density over sea ice play crucial role in the estimation of sea ice thickness.  相似文献   

Increasing imposex in populations of Bolinus brandaris (Gastropoda: Muricidae) in the northwestern Mediterranean.     

M Ramón  M J Amor 《Marine environmental research》2001,52(5):463-475

The muricid gastropod Bolinus brandaris exhibited imposex, a phenomenon linked to the use of organotin biocides. Several stages of imposex development (1-5) could be distinguished and were documented with SEM-photographs for the first time in this species. Additional alterations of the genital tract in females (blocked vulva preventing copulation and deposition of egg capsules) and males (excrecences on the penis and vas deferens) were shown. Imposex intensity on the Catalan coast was very high. The frequency of imposex off Barcelona and Vilanova i la Geltrú was 100%, with all females showing stage 4. Imposex frequency off Sant Carles de la Ràpita was 99.7% and the VDS index scored 3.9. Despite regulations of TBT-containing antifouling paints in Spain since 1990, the present study revealed that frequency and intensity of imposex have increased on the Catalan coast, at least since 1997. However, at present, imposex does not apparently affect the population dynamics of B. brandaris in the studied area, since no serious consequences on female reproduction (only one case of female sterilization) were detected. Gonadal activity and oogenesis were not suppressed or supplanted by spermatogenesis. Sex ratios were not male-biased. Possible sources of organotin biocides are examined.  相似文献   

Hall effects on hydromagnetic convection flow in a rotating fluid     

P. C. Ram 《Astrophysics and Space Science》1989,158(2):189-195

An analysis of Hall effects on the hydromagnetic free convection resulting from the combined effects of thermal and mass diffusion of an electrically-conducting liquid passed an infinite vertical porous plate in a rotating frame of reference is carried out when a strong magnetic field is imposed in a plane which makes an angle with the normal to the plate. The expressions for the mean velocity, mean temperature in the boundary layer, and the mean skin-friction, the mean rate of heat transfer on the plate are derived. The influence of Hall currents on the flow is studied for various values of .  相似文献   

Hall effects on heat and mass transfer flow with variable suction and heat generation     

H. S. Takhar  P. C. Ram  S. S. Singh 《Astrophysics and Space Science》1992,191(1):101-106

A study of the combined buoyancy effects of thermal and mass diffusion on MHD convection flow in the presence of Hall currents with variable suction and heat generation has been carried out. Analytical expressions for the velocity and the temperature of the fluid are given. The effects of Hall currents, parameterm, and heat source parameter on the velocity are discussed.  相似文献   

Fluid Geochemistry as Indicator of Tectonically-Related,Deep Water Circulations in the Sardinian Rift-Campidano Graben (Italy): New Insights from Environmental Isotopes     

Elisa Sacchi  Gian Maria Zuppi  Luca Pizzino  Fedora Quattrocchi  Salvatore Lombardi 《Aquatic Geochemistry》2008,14(4):301-319

The EC funded Geochemical Seismic Zonation program (EEC GSZ Project 1996–1998) chose Sardinia as a low-seismicity site, in which the relationships between fluid geochemistry and seismo-tectonics had to be investigated and results compared with outcomes from other selected high-seismicity sites. A first article, examining the role of fault segmentation and seismic quiescence on the geochemical composition of groundwaters and gases, has already been presented (Angelone et al. 2005). This article deals with environmental isotopes which, together with selected hydrochemical data, give hints on tectonically-related fluid circulations. Four water-dominated hydrothermal systems were considered, all located along regional fault systems and discharging groundwaters belonging to the Na–HCO₃ and Na–Cl facies. In the considered systems, groundwater circulation takes place, principally, in the Palaeozoic Crystalline Basement (PCB), with the exception of the Logudoro system, where hydrological circuits develop in the Mesozoic Carbonate Platform (MCP). The high CO₂ contents, the non-attainment of fluid-rock equilibrium and the large lithological variability prevent the construction of a unique hydrogeological–geochemical conceptual model. In this case, stable isotopes provide a useful tool to describe the origin of fluids and their subterranean movements. Stable isotopes of water, integrated with hydrochemical data, indicate that fluids are derived from three main end members. The dominant component is a relatively recent local meteoric water; the second one is marine water; and the third one is a fossil freshwater, depleted in heavy isotopes with respect to modern rains. The latter end member entered the aquifer system in the past, when climatic conditions were greatly different from today. At least two circulation systems can be recognised, namely a shallow cold system and a deep hydrothermal system, as well as two distinct hydrological processes: (1) gravity-controlled descent of cold water towards greater depths and (2) convection linked to a thermal gradient, causing deep fluids to rise up from the hydrothermal reservoir towards the surface. The highly variable δ¹³C_TDIC values suggest the presence of two distinct CO₂ sources, namely, a biogenic one and a thermogenic one. The relation between the isotopic compositions of CO₂ and He indicates an increased mantle signature in uprising CO₂-rich fluids.  相似文献   

Cosmological models in certain scalar-tensor theories     

Shri Ram  J. K. Singh 《Astrophysics and Space Science》1995,234(2):325-334

Exact solutions of Einstein field equations are obtained in the scalar-tensor theories developed by Saez and Ballester (1985) and Lau and Prokhovnik (1986) when the line-element has the form $$ds^2 = \exp \left( {2h} \right)dt^2 - \exp \left( {2A} \right)\left( {dx^2 + dy^2 } \right) - \exp \left( {2B} \right)dz^2 $$ whereh, A andB are functions oft only. The solutions are spatially homogeneous, locally rotationally symmetric and admit a Bianchi I group of motions on hypersurfacest = constant. The dynamical behaviours of these models have also been discussed.  相似文献   

Effects of hall current on the hydromagnetic free convection with mass transfer in a rotating fluid     

H. L. Agrawal  P. C. Ram  V. Singh 《Astrophysics and Space Science》1984,100(1-2):279-286

An exact analysis of Hall current on hydromagnetic free convection with mass transfer in a conducting liquid past an infinite vertical porous plate in a rotating fluid has been presented. Exact solution for the velocity field has been obtained and the effects ofm (Hall parameter),E (Ekman number), andS _c (Schmidt number) on the velocity field have been discussed.Nomenclature C species concentration - C _w concentration at the porous plate - C species concentration at infinity - C _p specific heat at constant pressure - D chemical molecular diffusivity - g acceleration due to gravity - E Ekman number - G Grashof number - H ₀ applied magnetic field - j _x, j_y, j_z components of the current densityJ - k thermal conductivity - M Hartman number - m Hall parameter - P Prandtl number - Q heat flux per unit area - S _c Sehmidt number - T temperature of the fluid near the plate - T _w temperature of the plate - T temperature of the fluid in the free-stream - u, v, w components of the velocity fieldq, - U uniform free stream velocity - w ₀ suction velocity - x, y, z Cartesian coordinates - Z dimensionless coordinate normal to the plate. Greek symbols coefficient of volume expansion - ^* coefficient of expansion with concentration - _e cyclotron frequency - dimensionless temperature - ^* dimensionless concentration - v kinematic viscosity - density of the fluid in the boundary layer - coefficient of viscosity - _e magnetic permeability - angular velocity - electrical conductivity of the fluid - _e electron collision time - _u skin-friction in the direction ofu - _v skin-friction in the direction ofv  相似文献   

Incoherent Cerenkov process as a source of low-latitude VLF emissions     

Ram Prakash  D.P. Singh  Birbal Singh 《Planetary and Space Science》1979,27(7):959-962

Employing a realistic ionospheric model and a suitable energetic electron spectra, detailed power calculations are carried out to confirm the generation mechanism of low-latitude VLF emissions observed both in the satellites and on the ground. Raypaths of the radiated waves are also calculated to account for the attenuation and spreading losses. It is shown that 100 eV?1 keV electrons radiating incoherently in the Cerenkov mode are the main sources of these emissions.  相似文献   

Heat and mass transfer of a viscous heat generating fluid with Hall currents     

P. C. Ram  S. S. Singh  R. K. Jain 《Astrophysics and Space Science》1990,168(2):209-216

A study of natural convection in hydrodynamic flows of a viscous heat generating fluid in the presence of Hall currents and variable suction has been carried out. The governing equations for the magnetohydrodynamic fluid flow and heat transfer are solved. The effects of Hall currentm and heat source parameter on the velocity and temperature distributions are discussed.  相似文献   

Elucidation of different forms of organic carbon in marine sediments from the Atlantic coast of Spain using thermal analysis coupled to isotope ratio and quadrupole mass spectrometry     

Elisa Lopez Capel  Jos Maria de la Rosa Arranz  Francisco J. Gonzlez-Vila  Jos Antonio Gonzlez-Perez  David A.C. Manning 《Organic Geochemistry》2006,37(12):1983

Analysis of river, estuary and marine sediments from the Atlantic coast of Spain using thermogravimetry–differential scanning calorimetry–quadrupole mass spectrometry–isotope ratio mass spectrometry (TG–DSC–QMS–IRMS) was used to (a) distinguish bulk chemical hosts for C within a sediment and humic acid fraction, (b) track C pools with differing natural C isotope ratios and (c) observe variation with distance from the coast. This is the first application of such a novel method to the characterisation of organic matter from marine sediments and their corresponding humic acid fractions. Using thermal analysis, a labile, a recalcitrant and a refractory carbon pool can be distinguished. Extracted humic fractions are mainly of recalcitrant nature. The proportion of refractory carbon is greatest in marine sediments and humic acid fractions. Quadrupole mass spectrometry confirmed that the greatest proportion of m/z 44 (CO₂) and m/z 18 (H₂O) were detected at temperatures associated with recalcitrant carbon (510–540 °C). Isotope analysis detected progressive enrichment in δ¹³C for the sediment samples with an increase in marine influence. Isotopic heterogeneity in the refractory organic matter in marine sediments could be due to products of anthropogenic origin or natural combustion products. Isotope homogeneity of humic acids confirms the presence of terrigenous C in marine sediments, allowing the terrestrial input to be characterised.  相似文献