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排序方式: 共有141条查询结果,搜索用时 31 毫秒
41.
European Venus Explorer (EVE): an in-situ mission to Venus 总被引:1,自引:0,他引:1
E. Chassefière O. Korablev T. Imamura K. H. Baines C. F. Wilson D. V. Titov K. L. Aplin T. Balint J. E. Blamont C. G. Cochrane Cs. Ferencz F. Ferri M. Gerasimov J. J. Leitner J. Lopez-Moreno B. Marty M. Martynov S. V. Pogrebenko A. Rodin J. A. Whiteway L. V. Zasova J. Michaud R. Bertrand J.-M. Charbonnier D. Carbonne P. Raizonville 《Experimental Astronomy》2009,23(3):741-760
The European Venus Explorer (EVE) mission was proposed to the European Space Agency in 2007, as an M-class mission under the
Cosmic Vision Programme. Although it has not been chosen in the 2007 selection round for programmatic reasons, the EVE mission
may serve as a useful reference point for future missions, so it is described here. It consists of one balloon platform floating
at an altitude of 50–60 km, one descent probe provided by Russia, and an orbiter with a polar orbit which will relay data
from the balloon and descent probe, and perform science observations. The balloon type preferred for scientific goals is one
which oscillates in altitude through the cloud deck. To achieve this flight profile, the balloon envelope contains a phase
change fluid, which results in a flight profile which oscillates in height. The nominal balloon lifetime is 7 days—enough
for one full circumnavigation of the planet. The descent probe’s fall through the atmosphere takes 60 min, followed by 30 min
of operation on the surface. The key measurement objectives of EVE are: (1) in situ measurement from the balloon of noble
gas abundances and stable isotope ratios, to study the record of the evolution of Venus; (2) in situ balloon-borne measurement
of cloud particle and gas composition, and their spatial variation, to understand the complex cloud-level chemistry; (3) in
situ measurements of environmental parameters and winds (from tracking of the balloon) for one rotation around the planet,
to understand atmospheric dynamics and radiative balance in this crucial region. The portfolio of key measurements is complemented
by the Russian descent probe, which enables the investigation of the deep atmosphere and surface. 相似文献
42.
43.
Anabela Carvalho Mike D. Flannigan Kim A. Logan Lynn M. Gowman Ana Isabel Miranda Carlos Borrego 《Climatic change》2010,98(1-2):177-197
In this study, we investigated the impact of future climate change on fire activity in 12 districts across Portugal. Using historical relationships and the HIRHAM (High Resolution Hamburg Model) 12 and 25 km climate simulations, we assessed the fire weather and subsequent fire activity under a 2 × CO2 scenario. We found that the fire activity prediction was not affected by the spatial resolution of the climate model used (12 vs. 25 km). Future area burned is predicted to increase 478% for Portugal as a whole, which equates to an increase from 1.4% to 7.8% of the available burnable area burning annually. Fire occurrence will also see a dramatic increase (279%) for all of Portugal. There is significant spatial variation within these results; the north and central districts of the country generally will see larger increases in fire activity. 相似文献
44.
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46.
Climate change that results from increasing levels of greenhouse gases in the atmosphere has the potential to increase temperature and alter rainfall patterns across the boreal forest region of Canada. Daily output from the Canadian Climate Centre coupled general circulation model (GCM) and the Hadley Centre's HadCM3 GCM provided simulated historic climate data and future climate scenarios for the forested area of the province of Ontario, Canada. These models project that in climates of increased greenhouse gases and aerosols, surface air temperatures will increase while seasonal precipitation amounts will remain relatively constant or increase slightly during the forest fire season. These projected changes in weather conditions are used to predict changes in the moisture content of forest fuel, which influences the incidence of people-caused forest fires. Poisson regression analysis methods are used to develop predictive models for the daily number of fires occurring in each of the ecoregions across the forest fire management region of Ontario. This people-caused fire prediction model, combined with GCM data, predicts the total number of people-caused fires in Ontario could increase by approximately 18% by 2020–2040 and50% by the end of the 21st century. 相似文献
47.
Jenny E. Goldstein Laura Graham Sofyan Ansori Yenni Vetrita Andri Thomas Grahame Applegate Andrew P. Vayda Bambang H. Saharjo Mark A. Cochrane 《Singapore journal of tropical geography》2020,41(2):190-208
Near-annual landscape-scale fires in Indonesia's peatlands have caused severe air pollution, economic losses, and health impacts for millions of Southeast Asia residents. While the extent of fires across the peatland surface has been widely attributed to widespread peatland drainage for plantation agriculture, fires that transition from surface into sub-surface soil-based fires are the source of the most dangerous air pollution. Yet the mechanisms by which this transition occurs have rarely been considered, particularly in diversely managed landscapes. Integrating physical geography methods, including active fire scene evaluations and hydrological monitoring, with qualitative methods such as retrospective fire scene evaluations and semi-structured interviews, this article discusses how and why sub-surface peat fire transition occurs in an intensively altered peatland ecosystem in Indonesia's Central Kalimantan province. We demonstrate that variable water table levels and flammable surface vegetation (fire fuels) are co-produced socio-political and biophysical phenomena that enable the conditions in which surface fire is likely to transition into peat fire and increase landscape vulnerability to ongoing, uncontrollable annual fires. This localized understanding of peat fire transition counters normative causal narratives of tropical fire such as ‘slash-and-burn’, with implications for the management of new fire regimes in inhabited landscapes. 相似文献
48.
A. T. Jones J. M. Kennard G. A. Logan E. Grosjean J. Marshall 《Geo-Marine Letters》2009,29(4):233-248
Multibeam swath bathymetric data collected in 95–120 m water depth on Australia’s North West Shelf revealed two distinct populations
of sand waves: a laterally extensive, low-amplitude composite form comprising superimposed dunes and ripples, and a laterally
restricted form which has unusually high bedform heights and slopes. These large subaqueous sand waves comprise bioclastic
ooid/peloid sand. Significantly, evidence of seabed fluid flow was detected in association with the high-amplitude sand waves.
This evidence includes seabed pockmarks approximately 2–15 m in diameter imaged with side-scan sonar, tubular and massive
carbonate concretions dredged from the seabed, and potential active venting of a fluid plume from the seabed observed during
an underwater camera tow. Molecular and isotopic analyses of carbonate concretions collected from within pockmarks associated
with the high-amplitude sand waves indicate that the fluids from which they precipitated comprise modern seawater and are
not related to thermogenic fluids or microbial gases. The fluid flow is interpreted to be driven by macrotidal currents flowing
over the relatively steep slopes of the high-amplitude sand waves. Pockmarks and carbonate concretions then develop where
the interstitial flows are confined and focused by subsurface ‘mounds’ in a shallow seismic reflector. 相似文献
49.
Acoustic echoes obtained during high-resolution shallow marine seismic surveys contain information about the statistical nature of the sedimentary bottom and its spatial variability. Use of a broad-band seismic source and an appropriately chosen data acquisition window makes the acoustic responses particularly amenable to quantitive analysis. The work reported utilizes experimental frequency-domain spatial coherence functions of along-track acoustic echoes as empirical metrics of bottom character, and by virtue of their correlation with known sediment types, as objective bases for remote sediment classification. Theoretical relationships between parameters describing sediment surface topographies and echo coherence are derived for the case of dominant water-sediment interface acoustic scattering. The diverse experimental data base was acquired from the Grand Banks of Newfoundland using a 1- to 10-kHz Huntec DTS system. Bottom photographs, cores, and grab samples combined with expert geological synthesis provide qualitative and quantitative control. 相似文献
50.
Future Area Burned in Canada 总被引:16,自引:3,他引:16
M. D. Flannigan K. A. Logan B. D. Amiro W. R. Skinner B. J. Stocks 《Climatic change》2005,72(1-2):1-16
Historical relationships between weather, the Canadian fire weather index (FWI) system components and area burned in Canadian
ecozones were analysed on a monthly basis in tandem with output from the Canadian and the Hadley Centre GCMs to project future
area burned. Temperature and fuel moisture were the variables best related to historical monthly area burned with 36–64% of
the variance explained depending on ecozone. Our results suggest significant increases in future area burned although there
are large regional variations in fire activity. This was especially true for the Canadian GCM where some ecozones show little
change in area burned, however area burned was not projected to decrease in any of the ecozones modelled. On average, area
burned in Canada is projected to increase by 74–118% by the end of this century in a 3 × CO2 scenario. These estimates do not explicitly take into account any changes in vegetation, ignitions, fire season length, and
human activity (fire management and land use activities) that may influence area burned. However, the estimated increases
in area burned would have significant ecological, economic and social impacts for Canada. 相似文献