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211.
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Michael A. Mischna Mark Allen Mark I. Richardson Claire E. Newman Anthony D. Toigo 《Planetary and Space Science》2011,59(2-3):227-237
We utilize the MarsWRF general circulation model (GCM) to address the behavior of gas plumes in the Martian atmosphere, with the specific goal of characterizing the source of the recently identified methane detection in the Martian atmosphere. These observations have been interpreted as the release of methane from localized surface sources with spatial and temporal variabilities. Due to the limited temporal coverage of ground-based observations, we use a GCM to simulate the development of passive atmospheric plumes over relevant timescales. The observations can be reproduced best if the release occurred just before the time of observation—no more than 1–2 sols earlier—and if this release were nearly instantaneous rather than a slow, steady emission. Furthermore, it requires a source region spanning a broad latitudinal range rather than a point emission. While the accuracy of our conclusions about this specific methane release scenario is limited by the uncertainties inherent in GCM simulations of the Martian atmosphere, our findings regarding generalized plume behavior are robust, and illustrate the potential power of numerical modeling for constraining plume source conditions. 相似文献
214.
Laboratory experiments have shown that the juvenile migratory stage of banded kokopu (Galaxias fasciatus (Gray 1842)) is more sensitive to turbidity than other native fish species and avoids turbidity levels of >25 nephelometric turbidity units (NTU). Field trials using juvenile fish collected from the Tarawera River and Hays Stream, New Zealand, were used to test the results from these laboratory experiments by measuring the effects of turbidity on the migration direction and rate for banded kokopu in a natural stream setting. In the stream setting, neither the migration rate nor the migration direction were affected at turbidity <25 NTU. At higher turbidity levels, significantly fewer fish migrated up stream within a given time period. Because there was rarely any downstream movement, this suggests the fish either halted or slowed their upstream movement. A slower rate of migration could result in fewer juveniles reaching adult habitat, and would account for the reduced abundance of adult banded kokopu in rivers that are turbid during the migration season. Achieving turbidity levels of <25 NTU in rivers and streams during the migration season would therefore help maintain upstream migrations and populations of banded kokopu, and hence other native fish species. 相似文献
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对于地震物理学和断裂运动研究而言,探索断裂带构造和地震行为之间的联系是至关重要的。地震代表滑动行为的一个极端;摩擦熔融和假玄武玻璃为动力破裂过程中的局部滑动提供了野外证据[1-3]。无震滑动则 相似文献
217.
Cross-ecosystem subsidies, such as terrestrial invertebrates and leaf litter falling into water as resources for aquatic communities,
can vary across environmental gradients. We examined whether the effect of terrestrial subsidy inputs on benthic invertebrates
was mediated by resident coastal cutthroat trout (Oncorhynchus clarki) in two representative streams. We experimentally manipulated the input rates (reduced, ambient) of terrestrial subsidies
(terrestrial invertebrates and leaf litter) as well as the presence or absence of cutthroat trout in the two streams. The
hypothesis that the reduction of terrestrial subsidies to the stream influences benthic invertebrate assemblages was supported
by experimental results. The treatments of terrestrial subsidy reduction and cutthroat trout presence had a significant negative
effect on benthic invertebrate community biomass and shredder biomass in East Creek with high natural terrestrial subsidy
input and small amount of large wood in channel. In contrast, results from Spring Creek with low subsidy input and large amount
of large wood in channel showed that only the terrestrial subsidy reduction significantly reduced the biomass of shredders.
The effects of the terrestrial subsidy input and trout predation on benthic invertebrate communities varied between the two
streams. Our results indicate that a subsidy effect on benthic communities can vary between nearby streams differing in canopy
and habitats. This study, with the major finding of highly context-dependent effects of spatial subsidies, suggests that the
interplay of resource subsidies and predators on invertebrate community assemblages can be site-specific and context-dependent
on habitat features. 相似文献
218.
Non-stationary Generation of Weak Turbulence for Very Stable and Weak-Wind Conditions 总被引:4,自引:4,他引:0
Larry Mahrt Christoph Thomas Scott Richardson Nelson Seaman David Stauffer Matthias Zeeman 《Boundary-Layer Meteorology》2013,147(2):179-199
Turbulence measurements for very stable conditions near the surface are contrasted among three sites: a high altitude basin during winter with grass or snow-covered grass, a broad valley with complex agricultural land use, and a more narrow valley that is influenced by a valley cold pool and cold air drainage. In contrast to previous studies, this investigation emphasizes the very weak turbulence with large bulk Richardson number occurring during extensive periods between brief mixing events. The relationship of the turbulence to the non-stationary wind and stratification is examined along with the impact of short-term flow accelerations, directional shear and downward diffusion of turbulence from higher levels. The failure of the turbulence for strong stratification to decrease with further increase of stratification is explored. Additional analyses are applied to weak-wind cases for the entire range of stratification, including weak stratification associated with cloudy conditions. 相似文献
219.
We determined how the species used for calibration affects the accuracy of in situ chlorophyll a (chl a) measurements by fluorometry using single-species cultures and natural phytoplankton populations from Winyah Bay, South Carolina,
USA. When a diatom was used for calibration, chl a in a dinoflagellate culture was overestimated by 66 ± 7%, whereas concentrations of a cryptophyte, chlorophyte, and cyanobacterium
were underestimated by 16 ± 20%, 40 ± 7%, and 71 ± 33%, respectively. In natural populations, the combination of species-specific
and environmentally induced variation in the ratio of fluorescence to chl a (F Chl−1) led to an overestimate by the in situ fluorometer of 40–169% for an April experiment and an underestimate of 4–50% in July.
Even when field samples were dominated by diatoms, environmental effects resulted in highly variable predictions of chl a. Thus, while a carefully selected calibration species can improve estimates of in vivo chl a in the laboratory, calibration of in situ fluorometers should be done with natural communities collected from the site of
interest. 相似文献
220.