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11.
M. N. Khaliq P. Gachon A. St-Hilaire T. B. M. J. Ouarda B. Bobée 《Theoretical and Applied Climatology》2007,88(1-2):83-101
Summary Summer-season (May–September) daily maximum temperature (T
max) and daily minimum temperature (T
min) observations and three types of heat spells obtained from these temperature observations at seven weather stations located
in southern Quebec (Canada) for the 60-year period from 1941 to 2000 are studied to assess temporal changes in their characteristics
(i.e. frequency of occurrence, seasonal hot days and extremal durations of heat spells). Type-A and Type-B heat spells are
obtained respectively from T
max and T
min observations and Type-C heat spells from simultaneous joint observations of T
max and T
min using suitable thresholds and spells of duration ≥1-day and ≥3-day. The results of this investigation show that the majority
of the selected percentiles (i.e. 5P, 10P, 25P, 50P, 75P, 80P, 90P, 92P, 95P, and 98P) of T
max observations show a negative time-trend with statistically significant decreases (at 10% level) in some of the higher percentiles
and in the maximal values at four out of seven stations. Almost all of the selected percentiles (same as for the T
max) and the maximal and minimal values of T
min observations show a positive trend, with statistically significant increases for all seven stations. Examination of frequencies
of occurrence of heat spells, seasonal hot days and annual extremes of heat spell durations indicate that many of these characteristics
of heat spells have undergone statistically significant changes over time at some of the stations for Type-A and Type-B heat
spells as compared to Type-C heat spells. The Type-C heat spells are generally small in number and are found to be relatively
temporally stable. More severe Type-C heat spells, i.e. the ones having T
max and T
min values simultaneously above very high thresholds and with duration ≥3-day have been rarely observed in southern Quebec. 相似文献
12.
A global positioning system and ground penetrating radar surveys is used to produce digital elevation models of the surface and bed of Brewster Glacier. These are used to derive maps of subglacial hydraulic potential and drainage system structure using three different assumptions about the subglacial water pressure (Pw): (i) Pw = ice overburden; (ii) Pw = half ice overburden; (iii) Pw = atmospheric. Additionally, 16 dye‐tracing experiments at 12 locations were performed through a summer melt season. Dye return curve shape, together with calculations of transit velocity, dispersivity and storage, are used to infer the likely morphology of the subglacial drainage system. Taken together, the data indicate that the glacier is underlain by a channelised but hydraulically inefficient drainage system in the early summer in which water pressures are close to ice overburden. By mid‐summer, water pressures are closer to half‐ice overburden and the channelised drainage system is more hydraulically efficient. Surface streams that enter the glacier close to the location of major subglacial drainage pathways are routed quickly to the channels and then to the glacier snout. Streams that enter the glacier further away from the drainage pathways are routed slowly to the channels and then to the snout because they first flow through a distributed drainage system. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
13.
Shock-compressed MgO radiates thermally at temperatures between 2900 and 3700 K in the 170–200 GPa pressure range. A simple energy-transport model of the shocked-MgO-targets distinguishes between different shock-induced radiation sources in these targets and provides estimates of spectral absorption-coefficients, α ΛMgO , for shocked MgO (e.g. at 203 GPa, α ΛMgO ˜ 630, 7500, 4200 and 3800 m−1 , at 450, 600, 750 and 900 nm, respectively). The experimentally inferred temperatures of the shock-compressed states of MgO are consistent with temperatures calculated for MgO assuming that (1) it deforms as an elastic fluid, (2) has a Dulong-Petit value for specific heat at constant volume in its shocked state, and (3) undergoes no phase transformation below 200 GPa. 相似文献
14.
15.
Economics of geological CO2 storage and leakage 总被引:1,自引:0,他引:1
16.
Earle Williams Bob Boldi Anne Matlin Mark Weber Steve Hodanish Dave Sharp Steve Goodman Ravi Raghavan Dennis Buechler 《Atmospheric Research》1999,51(3-4)
The development of a new observational system called LISDAD (Lightning Imaging Sensor Demonstration and Display) has enabled a study of severe weather in central Florida. The total flash rates for storms verified to be severe are found to exceed 60 fpm, with some values reaching 500 fpm. Similar to earlier results for thunderstorm microbursts, the peak flash rate precedes the severe weather at the ground by 5–20 min. A distinguishing feature of severe storms is the presence of lightning ‘jumps' — abrupt increases in flash rate in advance of the maximum rate for the storm. The systematic total lightning precursor to severe weather of all kinds — wind, hail, tornadoes — is interpreted in terms of the updraft that sows the seeds aloft for severe weather at the surface and simultaneously stimulates the ice microphysics that drives the intracloud lightning activity. 相似文献
17.
18.
Research on gas hydrate has increased recently as an alternative to fossil fuel. This study of marine controlled source electromagnetics (CSEM) is motivated by this increase, particularly in deep waters, and examines representative models. We present 2D models and test their efficacy in detection and characterization of gas hydrates. Earlier modeling studies used a horizontal transmitter to study the CSEM response??two electrical and one magnetic component??for resistive subsurface layers. Here we use six components??three electrical and three magnetic??and show that the proposed method reduces ambiguity in interpretation. Additionally, we show results utilizing the transmitter dipole in a borehole and receivers at the sea bottom. We found that CSEM response from a vertical transmitter helps us characterize resistive layers more confidently than from a transmitter moving horizontally at sea bottom. We conclude that in a complex environment, combining horizontal and vertical movements of the transmitter with sea-bottom receivers helps us delineate the subsurface structure more clearly and may help reduce drilling costs. Our models closely match the gas hydrate region in the Gulf of Mexico??Walker Ridge Block-313. Although this study examines gas hydrate, the methodology is applicable to other areas??for example, in monitoring gas diffusion at subsurface depths, which may help in CO2 sequestration. 相似文献
19.
Mixed estimation methods for Halphen distributions with applications in extreme hydrologic events 总被引:3,自引:1,他引:2
Fateh Chebana Salaheddine El Adlouni Bernard Bobée 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(3):359-376
The Halphen family of distributions is a flexible and complete system to fit sets of observations independent and identically
distributed. Recently, it is shown that this family of distributions represents a potential alternative to the generalized
extreme value distributions to model extreme hydrological events. The existence of jointly sufficient statistics for parameter
estimation leads to optimality of the method of maximum likelihood (ML). Nevertheless, the ML method requires numerical approximations
leading to less accurate values. However, estimators by the method of moments (MM) are explicit and their computation is fast.
Even though MM method leads to good results, it is not optimal. In order to combine the advantages of the ML (optimality)
and MM (efficiency and fast computations), two new mixed methods were proposed in this paper. One of the two methods is direct
and the other is iterative, denoted respectively direct mixed method (MMD) and iterative mixed method (MMI). An overall comparison
of the four estimation methods (MM, ML, MMD and MMI) was performed using Monte Carlo simulations regarding the three Halphen
distributions. Generally, the MMI method can be considered for the three Halphen distributions since it is recommended for
a majority of cases encountered in hydrology. The principal idea of the mixed methods MMD and MMI could be generalized for
other distributions with complicated density functions. 相似文献
20.
Anthony Snider Jeffery HillShanhong Luo Bob BuergerJim Herstine 《Ocean & Coastal Management》2011,54(8):612-620
This study determined the characteristics of North Carolina Coastal Reserve and North Carolina National Estuarine Research Reserve (jointly referred to as Reserve) visitors, visitor opinions of site conditions, visitor understanding of site management objectives, and patterns of visitation. The latter were investigated to obtain a proxy of place attachment and its effects on knowledge of ownership and perceptions of management. Data were collected on demographics, use patterns, visitor perceptions, and visitor knowledge during the period of 25 May-28 October, 2007. Visitors were educated, wealthy, older, racially homogeneous, and frequent returnees. The majority of respondents supported existing management activities and the implementation of additional use restrictions should site conditions deteriorate. Data indicated that respondents were unaware of which agency manages the Reserve sites or its mission. These findings suggest that management needs to engage in more education of the visiting public. Sensitizing the public to the mission of the Reserve and increasing place attachment could decrease negative visitor impacts. 相似文献