Assessment of glacial lake development and downstream flood impacts of critical glacial lake     

Goswami  Uttam Puri  Goyal  Manish Kumar 《Natural Hazards》2021,109(1):1027-1046

Natural Hazards - Glacial lakes are rapidly growing in response to climate change and glacier retreat which may lead to catastrophic socio-economic disasters. The failure of moraine-dammed lakes is...  相似文献   

Paleo-ocean chemistry records in marine opal: Implications for fluxes of trace elements, cosmogenic nuclides (Be and Al), and biological productivity     

D. Lal  C. Charles  J.N. Goswami  L. McHargue 《Geochimica et cosmochimica acta》2006,70(13):3275-3289

Here, we provide evidence suggesting that marine (diatom) opal contains not only a high fidelity record of dissolved oceanic concentrations of cosmic ray-produced radionuclides, ¹⁰Be and ²⁶Al, but also a record of temporal variations in a large number of trace elements such as Ti, Fe, Zn and Mn. This finding is derived from measurements in purified biogenic opal that can be separated from detrital materials using a newly developed technique based on surface charge characteristics. Initial results from a sediment core taken near the present-day position of the Antarctic Polar Front (ODP Site 1093) show dramatic changes in the intrinsic concentrations of, Be, Al, Ti, Fe, Mn and Zn in the opal assemblages during the past ∼140 kyr BP. The results imply appreciable climatically controlled fluctuations in the level of bioreactive trace elements. The time series of total Be, Al, Ti, Fe and ¹⁰Be in the sediment core are all well correlated with each other and with dust records in the polar ice cores. The observations suggest that a significant flux of these trace metals to oceans is contributed by the aeolian dust, in this case, presumably from the Patagonia. This observation also allows determination of fluxes of dust-contributed ¹⁰Be to the Antarctica ice sheets. However, our data show that the relationships among the various metals are not perfectly linear. During periods of higher dissolved concentrations of trace elements (indicated by Fe and Ti) the relative concentrations of bioreactive elements, Be, Al, Mn and Zn are decreased. By contrast, the Fe/Zn and Fe/Mn ratios decrease significantly during each transition from cold to warm periods. The relative behavior could be consistent with any of the following processes: (i) enhanced biological productivity due to greater supply of the bioreactive elements (e.g. Zn) during cold periods (ii) increased biological and inorganic scavenging of particle active elements (e.g. Be and Al) during early interglacial periods (iii) differential uptake/removal of the metals by the various diatom taxa whose relative productivity or growth rate changes with large scale climate. In any case, with one sedimentary phase and in single sedimentary sections, we now have the potential to compare directly a proxy for aeolian input of micronutrients (e.g. Fe or Ti), with a proxy for production (e.g. ²⁶Al/Al ratios). We expect that studies of the temporal records of trace elements and cosmogenic nuclides in contrasting regions of upwelling and productivity, which exhibit different sensitivities to global climate fluctuations and micronutrient inputs, would lead to a direct and comprehensive test of ideas such as the hypothesis of iron control of atmospheric carbon dioxide [Martin, J.H., 1990. Glacial-interglacial CO₂ change: the iron hypothesis. Paleoceanography5, 1-13]. Our present data from a single site do not show that increases in dissolved Fe concentrations, per se, were responsible for increased biological productivity. However, a much clearer picture of the effect of increased dust fluxes should emerge when we have data for trace elements and the cosmogenic nuclides, ¹⁰Be and ²⁶Al from various oceanic provinces.  相似文献   

Street Versus Rooftop Level Concentrations of Fine Particles in a Cambridge Street Canyon     

Prashant Kumar  Paul S. Fennell  Allan N. Hayhurst  Rex E. Britter 《Boundary-Layer Meteorology》2009,131(1):3-18

Dispersion of particles, as evidenced by changes in their number distributions (PNDs) and concentrations (PNCs), in urban street canyons, is still not well understood. This study compares measurements by a fast-response particle spectrometer (DMS500) of the PNDs and the PNCs (5–1000 nm, sampled at 1 Hz) at street and rooftop levels in a Cambridge UK street canyon, and examines mixing, physical and chemical conversion processes, and the competing influences of traffic volume and rooftop wind speed on the PNDs and the PNCs in various size ranges. PNCs at street level were ≈6.5 times higher than at rooftop. Street-level PNCs followed the traffic volume and decreased with increasing wind speed, showing a larger influence of wind speed on 30–300 nm particles than on 5–30 nm particles. Conversely, rooftop PNCs in the 5–30 nm size range increased with wind speed, whereas those for particles between 30 and 300 nm did not vary with wind speed.  相似文献   

26Al as a heat source for early melting of planetesimals: Results from isotopic studies of meteorites     

S. Sahijpal  M. A. Ivanova  L. L. Kashkarov  N. N. Korotkova  L. F. Migdisova  M. A. Nazarov  J. N. Goswami 《Journal of Earth System Science》1995,104(4):555-567

Ion microprobe studies of magnesium isotopic composition in igneous components from several chondritic meteorites have been carried out to look for²⁶Mg excess that may be attributed to the presence of the now-extinct radionuclide²⁶Al(τ ∼ 1 Ma) at the time of formation of these objects. A positive evidence for the presence of²⁶Al in the analysed objects will strengthen its case as the primary heat source for the early thermal metamorphism/melting of meteorite parent bodies. Based on calculated temperature profiles inside chondritic objects of different sizes and initial²⁶Al/²⁷Al ratios, we have estimated the initial abundances of²⁶Al needed to provide the heat necessary for the wide range of thermal processing seen in various types of meteorites. The magnesium isotopic data obtained by us do not provide definitive evidence for the presence of²⁶Al at the time of formation of the analysed igneous phases in different chondritic meteorites. Experimental evidence for a planetary scale distribution of²⁶Al in the early solar system to serve as a significant heat source for the thermal metamorphism and melting of meteorite parent bodies (planetesimals) remains elusive.  相似文献   

Incipient vortex size-dependent evolution of tropical disturbances Part I — Results from a numerical experiment     

P. Goswami  R. Koteswar Rao 《Journal of Earth System Science》1993,102(3):439-463

The present work is concerned with the study of intensification of tropical disturbances with a view to improve prediction and early warning. The tropical disturbances are known to come in sizes (radii) ranging from 100–400 kms. Since the vortices of different sizes give rise to different initial convergence fields and since the subsequent development of the tropical depressions is very sensitive to the initial convergence fields, we argue that the size of the incipient vortex is likely to be an important factor in determining the subsequent development of a tropical disturbance. We have examined the above hypothesis using an axisymmetric model of tropical cyclone. The incipient vortex is introduced by prescribing an initial temperature perturbation with wind in gradient balance. The results show a fairly sharp selection of scale at about 250 km radius. This implies that out of a number of initial disturbances of varying sizes and embedded in the same large scale environment, it is the vortex with about 250 km radius size that will develop to the most severe system. The sensitivity of this selective intensification at this incipient vortex radius to initial perturbation field and the mean thermodynamic state is investigated. Finally, the importance of such a selective scale of intensification for prediction, tracking and early warning of tropical cyclones is emphasized.  相似文献   

Irradiation history and atmospheric ablation of meteorites: Results from cosmic ray track studies     

J N Goswami 《Journal of Earth System Science》1981,90(4):345-358

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Windows to early solar system processes: Refractory inclusions in the CV and CM chondrites     

J D Macdougall  J N Goswami 《Journal of Earth System Science》1981,90(1):1-26

The refractory element-enriched inclusions found in the carbonaceous meteorites give cosmochemists a fascinating glimpse at processes which occurred near the birth of the solar system. Although many complications must still be unravelled, the weight of the available evidence indicates that many of these objects condensed directly from the solar nebula, and have remained relatively unaltered up to the present. Their mineralogical and chemical compositions therefore reflect conditions at the time of their formation. The most thoroughly studied of the inclusions are those from the Allende CV meteorite. These, in general, have mineral assemblages similar to those which would be predicted for nebular condensation. The mineralogical agreement is not strict, however, and also the bulk chemical compositions sometimes deviate markedly from expected trends. More work is required to understand these differences. A range of isotopic anomalies in many elements has been found, in these inclusions. Some of these suggest an extra-solar system origin for a part of the material in the inclusions. Although much less work has been done on the inclusions in the CM meteorites, current data indicate that they will prove to be at least as valuable as those from Allende. Chemical data show that some inclusions in the Murchison meteorite are more refractory than the most refractory Allende inclusions. Isotopic anomalies, including²⁵Mg excesses and oxygen-16 enriched oxygen, indicate that, in spite of chemical and mineralogical differences, the Murchison and Allende inclusions contain common isotopic components, and are probably contemporaneous.  相似文献   

Depositional history of Luna 24 drill core soil samples     

J.N. Goswami  D. Lal  M.N. Rao  T.R. Venkatesan 《Earth and Planetary Science Letters》1979,44(2):325-334

Six soil samples from various depths of the Luna 24 drill core column have been analysed for their particle track records and light noble gas compositions. The observed particle track records indicate higher degree of maturity for the upper zone (～1 m) of this regolith column as compared to the soils in the lower zone (～0.4 m). The cosmogenic²¹Ne concentrations decrease rapidly with depth to 1 m, after which the concentrations level off or increase slightly. These data suggest a multi-stage depositional history for this drill core soil column consisting of: (1) rapid deposition of regolith material, (2) a cratering event about 400 m.y. B.P., leading to excavation to a depth of ～1 m from the present regolith surface, (3) a relatively rapid fill up of the crater with near-surface irradiated material, and (4) in-situ irradiation during the last about 250–300 m.y. Such a depositional sequence can also explain the observed lack of correlation between different surface exposure-correlated maturity indices in these drill core soil samples.  相似文献   

Comparative Study of Nucleation by Different Alcoholic Solutions of Benzoin, and Benzoin Dust     

Sahana Paul  A. Hazra  U. K. De  S. Bhar  K. Goswami 《Journal of Atmospheric Chemistry》2006,53(2):155-168

Nucleation properties of different alcoholic solutions of Benzoin and Benzoin dust have been studied by varying the seeding temperature in a laboratory Cold Chamber. In the present study, three different alcoholic solutions are being used and these are due to the standard Ethyl alcohol, one higher alcohol i.e. Isopropyle alcohol and one lower alcohol i.e. Methyl alcohol. In addition, Benzil dust and droplets of Acetone and Chloroform have been used to examine if these agents have any ice nucleation ability. It has been observed that all alcoholic solutions of Benzoin have sufficient ice nucleation ability at the negative side of 0^°C, with the maximum concentration occurring at −14.4^°C. In case of Benzoin dust, the nucleation ability is better on the positive side of 0^°C than the negative side. On the other hand, Benzil dust has insignificant nucleation ability and the droplets of two other agents have no nucleation ability at all.Considering the chemical as well as crystalline structure, one can conclude that the presence of OH group in the seeding molecule plays the central role in ice nucleation/hydrate crystal formation. In fact, a number of supplementary experiments like crystal growth in an incubator, XRD analysis and NMR study are performed to identify the nature of crystals formed by Benzoin dust above 0^°C. One can conclude that these are hydrate crystals of Benzoin with water caging around Benzoin crystals.  相似文献   

Intraseasonal oscillations and interannual variability of surface winds over the Indian monsoon region     

B. N. Goswami  D. Sengupta  G. Suresh Kumar 《Journal of Earth System Science》1998,107(1):45-64

The role of intraseasonal oscillations (ISOs) in modulating synoptic and interannual variations of surface winds over the Indian monsoon region is studied using daily averaged National Centers for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalyses for the period 1987–1996. Two dominant ISOs are found in all years, with a period between 30–60 days and 10–20 days respectively. Although the ISOs themselves explain only about 10–25% of the daily variance, the spatial structure of variance of the ISOs is found to be nearly identical to that of high frequency activity (synoptic disturbances), indicating a significant control by the ISOs in determining the synoptic variations. Zonal and meridional propagation characteristics of the two modes and their interannual variability are studied in detail. The synoptic structure of the 30–60 day mode is similar in all years and is shown to be intimately related to the strong (‘active’) or weak (‘break’) phases of the Indian summer monsoon circulation. The peak (trough) phase of the mode in the north Bay of Bengal corresponds to the ‘active’ (‘break’) phase of monsoon strengthening (weakening) the entire large scale monsoon circulation. The ISOs modulate synoptic activity through the intensification or weakening of the large scale monsoon flow (monsoon trough). The peak wind anomalies associated with these ISOs could be as large as 30% of the seasonal mean winds in many regions. The vorticity pattern associated with the 30–60 day mode has a bi-modal meridional structure similar to the one associated with the seasonal mean winds but with a smaller meridional scale. The spatial structure of the 30–60 day mode is consistent with fluctuations of the tropical convergence zone (TCZ) between one continental and an equatorial Indian Ocean position. The 10–20 day mode has maximum amplitude in the north Bay of Bengal, where it is comparable to that of the 30–60 day mode. Elsewhere in the Indian Ocean, this mode is almost always weaker than the 30–60 day mode. In the Bay of Bengal region, the wind curl anomalies associated with the peak phases of the ISOs could be as large as 50% of the seasonal mean wind curl. Hence, ISOs in this region could drive significant ISOs in the ocean and might influence the seasonal mean currents in the Bay. On the interannual time scale, the NCEP/NCAR reanalysed wind stress is compared with the Florida State University monthly mean stress. The seasonal mean stress as well as interannual standard deviation of monthly stress from the two analyses agree well, indicating absence of any serious systematic bias in the NCEP/NCAR reanalysed winds. It is also found that the composite structure of the 30–60 day mode is strikingly similar to the dominant mode of interannual variability of the seasonal mean winds indicating a strong link between the ISOs and the seasonal mean. The ISO influences the seasonal mean and its interannual variability either through increased/decreased residence time of the TCZ in the continental position or through occurrence of stronger/weaker active/break spells. Thus, the ISOs seem to modulate all variability in this region from synoptic to interannual scales.  相似文献