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11.
Increasing urban albedo can reduce summertime temperatures, resulting in better air quality and savings from reduced air-conditioning costs. In addition, increasing urban albedo can result in less absorption of incoming solar radiation by the surface-troposphere system, countering to some extent the global scale effects of increasing greenhouse gas concentrations. Pavements and roofs typically constitute over 60% of urban surfaces (roof 20–25%, pavements about 40%). Using reflective materials, both roof and pavement albedos can be increased by about 0.25 and 0.15, respectively, resulting in a net albedo increase for urban areas of about 0.1. On a global basis, we estimate that increasing the world-wide albedos of urban roofs and paved surfaces will induce a negative radiative forcing on the earth equivalent to offsetting about 44 Gt of CO2 emissions. At ～$25/tonne of CO2, a 44 Gt CO2 emission offset from changing the albedo of roofs and paved surfaces is worth about $1,100 billion. Furthermore, many studies have demonstrated reductions of more than 20% in cooling costs for buildings whose rooftop albedo has been increased from 10–20% to about 60% (in the US, potential savings exceed $1 billion per year). Our estimated CO2 offsets from albedo modifications are dependent on assumptions used in this study, but nevertheless demonstrate remarkable global cooling potentials that may be obtained from cooler roofs and pavements. 相似文献
12.
Rajeev Menon P. V. Sunder Raju G. K. Reddy 《Journal of the Geological Society of India》2009,74(1):23-26
A geochemical soil sampling survey undertaken at Tumallpalle uranium mineralized zone Cuddapah district, has confirmed the
presence of uranium anomalies in soils. Bulk soil samples were collected at every 20 m along the traverse from approximately
30 cm below the surface and were assayed for uranium by x-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry
(ICP-MS). The uranium anomalies detected by the insitu radiometric survey show a correlation with the helium highs. The soil
gas helium studies have aided in delineating the subsurface extension of the deposit. This study endeavors for an integration
of different techniques in a known area which could probably aid in delineating uranium zones for optimal exploitation in
the future exploration programmes. 相似文献
13.
Phenology relates to the study of timing of periodic events in the life cycle of plants or animals as influenced by environmental conditions and climatic forcing. Phenological metrics provide information essential to quantify variations in the life cycle of these organisms. The metrics also allow us to estimate the speed at which living organisms respond to environmental changes. At the surface of the oceans, microscopic plant cells, so-called phytoplankton, grow and sometimes form blooms, with concentrations reaching up to 100 million cells per litre and extending over many square kilometres. These blooms can have a huge collective impact on ocean colour, because they contain chlorophyll and other auxiliary pigments, making them visible from space. Phytoplankton populations have a high turnover rate and can respond within hours to days to environmental perturbations. This makes them ideal indicators to study the first-level biological response to environmental changes. In the Earth’s climate system, the El Niño–Southern Oscillation (ENSO) dominates large-scale inter-annual variations in environmental conditions. It serves as a natural experiment to study and understand how phytoplankton in the ocean (and hence the organisms at higher trophic levels) respond to climate variability. Here, the ENSO influence on phytoplankton is estimated through variations in chlorophyll concentration, primary production and timings of initiation, peak, termination and duration of the growing period. The phenological variabilities are used to characterise phytoplankton responses to changes in some physical variables: sea surface temperature, sea surface height and wind. It is reported that in oceanic regions experiencing high annual variations in the solar cycle, such as in high latitudes, the influence of ENSO may be readily measured using annual mean anomalies of physical variables. In contrast, in oceanic regions where ENSO modulates a climate system characterised by a seasonal reversal of the wind forcing, such as the monsoon system in the Indian Ocean, phenology-based mean anomalies of physical variables help refine evaluation of the mechanisms driving the biological responses and provide a more comprehensive understanding of the integrated processes. 相似文献
14.
A. A. Fernandes Y. V. B. Sarma H. B. Menon P. Vethamony 《Journal of the Indian Society of Remote Sensing》2000,28(1):9-18
Gaussian smoothed SAR image spectra have been evaluated from 512 x 512 pixel subscenes of image mode ERS-1 SAR scenes off Goa, Visakhapatnam, Paradeep and Portugal. The two recently acquired scenes off Portugal showed the signature of swell of wavelength ≈ 200m and internal waves of wavelength > 400m. Only internal waves of wavelength > 400m were seen in the scene off Goa observed on 11 March 1992. The scenes off Visakhapatnam and Paradeep did not show any wave like features, the latter appearing to be of “white noise” nature. There exists a 180° ambiguity in wave direction observed from radar imageries. Based on the method of Atanassov et al (1985), a computer program has been developed for the removal of the 180° ambiguity by using two images of the same area separated by a time interval which is small compared to the period of the dominant waves. The computer program has been successfully tested with computer simulated images. 相似文献
15.
Directional spectrum of ocean waves from array measurements using phase/time/path difference methods 总被引：1，自引：0，他引：1
Wave direction has for the first time been consistently, accurately and unambiguously evaluated from array measurements using the phase/time/path difference (PTPD) methods of Esteva in case of polygonal arrays and Borgman in case of linear arrays. We have used time series measurements of water surface elevation at a 15-gauge polygonal array, in 8 m water depth, operational at the CERC's Field Research Facility at Duck, North Carolina, USA. Two modifications have been made in the methodology. One modification is that we use the true phase instead of the apparent phase, the other modification being that estimates of wave direction are registered only if the relevant gauges in the array are coherent at 0.01 significance level. PTPD methods assume that in a spectral frequency band the waves approach from a single direction, and are simple, expedient and provide redundant estimates of wave direction. Using Esteva's method with the above modifications, we found that at Duck: (i) the directions of swell and surf beat, when energetic swell is present, conform to the schematic diagram of surf beat generation given by Herbers et al., (ii) surf beat of remote origin occurs when the significant wave height, Hmo, falls below 0.41 m, (iii) the surf beat of remote origin is not normally incident at the shore contrary to Herbers et al. In fact we found that the surf beat of remote origin is incident at angles in excess of 45° with respect to the shore normal, and (iv) the surf beat of remote origin is largely trans-oceanic in origin. 相似文献
16.
K. B. Padmakumar B. R. Smitha Lathika Cicily Thomas C. L. Fanimol G. SreeRenjima N. R. Menon V. N. Sanjeevan 《Ocean Science Journal》2010,45(3):151-157
This study presents in situ evidence for the blooms of Trichodesmium erythraeum observed in the shelf waters of the South Eastern Arabian Sea (SEAS) during the onset of the southwest monsoon in June 2009. Evidence showed that water surface discoloration was caused by the accumulation of T. erythraeum, and that the water column contained a colony of T. thiebautii. The surface water color in the bloom region varied from pale brown to pinkish red. Pale brown indicated healthy algae at the peak of its photosynthetic activity, while pinkish red indicated the presence of photosynthetically less active filaments. Zooplankton abundance, especially copepodites, in the bloom area substantiated the theory that Trichodesmium filaments are excellent epiphytes to which the copepodites cling. The bloom area was very fertile with copious quantities of dissolved oxygen (6.85 ml L?1), PO4-P (0.108 μmol L?1) and SiO4 (1.29 μmol L?1). Lower NO3-N (0.028 μmol L?1) values in the bloom area did not appear to affect Trichodesmium growth from molecular nitrogen fixation. However, lower NO3-N values altered the normal phytoplankton composition of this area. 相似文献
17.
G. K. Reddy T. Seshunarayana Rajeev Menon P. Senthil Kumar 《Journal of Earth System Science》2010,119(5):745-751
Fracture and fault networks are conduits that facilitate groundwater movement in hard-rock terrains. Soil-gas helium emanometry
has been utilized in Wailapally watershed, near Hyderabad in southern India, for the detection of fracture and fault zones
in a granite basement terrain having a thin regolith. Based on satellite imagery and geologic mapping, three sites were selected
for detailed investigation. High spatial resolution soil-gas samples were collected at every one meter at a depth of >1.5m
along 100m long profiles (3 in number). In addition, deep shear-wave images were also obtained using the multichannel analysis
of surface waves. The study clearly indicates several soil-gas helium anomalies (above 200 ppb) along the profiles, where
the shear-wave velocity images also show many near-surface vertical low velocity zones. We thus interpret that the soil-gas
helium anomalous zones and the vertical low-velocity zones are probable traces of fault/fracture zones that could be efficient
natural recharge zones and potential groundwater conduits. The result obtained from this study demonstrates the efficacy of
an integrated approach of soil-gas helium and the seismic methods for mapping groundwater resource zones in granite/gneiss
provinces. 相似文献
18.
In the Hudson River estuary, fine mud and toxic metals are enriched in the upstream turbidity maximum. The mechanisms causing
the enrichment were assessed through the analysis of suspended-sediment concentration (SSC) (bottom and surface), particle
size, and trace metal distributions. Bottom SSCs varied across the study area by a factor of ten, and the turbidity maximum
activity was observed in between kilometers 45 and 80. The particle-size analysis defined two accumulation modes: <4.65 and
>22.1 μm. The ratio of the fine-to-coarse mode increased from 1.75 to 2.75 in the turbidity maximum. The fine mud concentration
(55–60%) in the turbidity maximum was found to have a high correlation (r=0.98;p<0.005) with the concentration of <2-μm particles. A conceptual model was derived in order to understand the possible mechanisms
by which fine mud (and specifically <2-μm particles) is concentrated. The two dominant size modes were analyzed for toxic
metals. The upstream tributaries are major sources of metals compared to point sources at downstream locations. In the turbidity
maximum, Cd, Cu, Zn, and Pb are significantly enriched compared to average shale metal values and ERM toxicity guidelines
by 580, 42, 10, 16 and 12, 7, 2.4, 1.4 times, respectively. Decreasing metal concentrations downstream of the turbidity maximum
imply that Haverstraw Bay acts as temporary storage for fine particles and enriched metals. It is demonstrated in this study
that toxic metals are enriched in Haverstraw Bay due to the mud accumulation. The high levels of toxic metals in the sediments
of the Hudson River estuary are a major concern because human activities (dredging and river traffic) cause resuspension of
sediments and can change the mobility patterns of bioavailable contaminants.
Received: 4 June 1997 · Accepted: 9 September 1997 相似文献
19.
Acta Geotechnica - Unsaturated clay is a heterogeneous porous medium consisting of three phases, namely solid soil skeleton, pore water, and pore air. It has been well recognized that the variation... 相似文献
20.
A probabilistic seismic hazard assessment at Kancheepuram in Southern India was carried out with the scope of defining the seismic input for the vulnerability assessment of historical and monumental structures at the site, in terms of horizontal Uniform Hazard Spectra and a suite of spectrum-compatible natural accelerograms to perform time-history analysis. The standard Cornell?CMcGuire and a zone-free approach have been used for hazard computations after the compilation of a composite earthquake catalogue for Kancheepuram. Epistemic uncertainty in the seismic hazard was addressed within a logic-tree framework. Deaggregation of the seismic hazard for the peak ground acceleration shows low seismicity at Kancheepuram controlled by weak-to-moderate earthquakes with sources located at short distances from the archaeological site. Suites of natural accelerograms recorded on rock have been selected by imposing a custom-defined compatibility criterion with the probabilistic spectra. The site of Kancheepuram is characterized by a seismicity controlled by weak-to-moderate earthquakes with sources at short distances from the site, the PGA expected for 475- and 2,475-year return period are, respectively, 0.075 and 0.132?g. The Indian code-defined spectra (DBE and MCE) tend to underestimate spectral ordinates at low periods. On the other hand, the PGA are comparable and the spectral ordinates for longer periods from the probabilistic study are significantly lower. 相似文献