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71.
Howard J. Falcon-Lang 《Geology Today》2005,21(5):178-181
It's hard to imagine the Rockies or the Alps without forests, but until about 360 million years ago the Earth's mountains were probably bare of vegetation. Almost a Martian landscape, this was a world of rocky screes, mudflows and flash floods. Lichen may have clung here and there, but as for large plants, most were restricted to wetland delta-plains close to sea level. But everything was about to change. The evolution of the seed in Late Devonian times altered the face of our planet forever. Analogous to the reptile egg in the animal kingdom, the seed freed plants from the necessity of surface water for reproduction, and paved the way for the invasion of mountainous terrain. 相似文献
72.
73.
R. D. Robinson R. T. Stewart N. R. Sheeley Jr. R. A. Howard J. Koomen D. J. Michels 《Solar physics》1986,105(1):149-171
An investigation is made to determine the relationship between a coronal mass ejection (CME) and the characteristics of associated metre-wave activity. It is found that (1) the CME width and leading edge velocity can be highly influential in determining the intensity, spectral complexity and frequency coverage of both type II and continuum bursts; (2) the presence of a CME is possibly a necessary condition for the production of a metric continuum event and (3) metric continuum bursts as well as intense, complex type II events are preferentially associated with strong, long lasting soft X-ray events. 相似文献
74.
75.
Nature,origin and evolution of a Late Pleistocene incised valley‐fill,Sunda Shelf,Southeast Asia
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Faisal A. Alqahtani Howard D. Johnson Christopher A.‐L. Jackson Mohd Rapi B. Som 《Sedimentology》2015,62(4):1198-1232
Understanding the stratigraphic fill and reconstructing the palaeo‐hydrology of incised valleys can help to constrain those factors that controlled their origin, evolution and regional significance. This condition is addressed through the analysis of a large (up to 18 km wide by 80 m deep) and exceptionally well‐imaged Late Pleistocene incised valley from the Sunda Shelf (South China Sea) based on shallow three‐dimensional seismic data from a large (11 500 km2), ‘merge’ survey, supplemented with site survey data (boreholes and seismic). This approach has enabled the characterization of the planform geometry, cross‐sectional area and internal stratigraphic architecture, which together allow reconstruction of the palaeo‐hydrology. The valley‐fill displays five notable stratigraphic features: (i) it is considerably larger than other seismically resolvable channel forms and can be traced for at least 180 km along its length; (ii) it is located in the axial part of the Malay Basin; (iii) the youngest part of the valley‐fill is dominated by a large (600 m wide and 23 m deep), high‐sinuosity channel, with well‐developed lateral accretion surfaces; (iv) the immediately adjacent interfluves contain much smaller, dendritic channel systems, which resemble tributaries that drained into the larger incised valley system; and (v) a ca 16 m thick, shell‐bearing, Holocene clay caps the valley‐fill. The dimension, basin location and palaeo‐hydrology of this incised valley leads to the conclusion that it represents the trunk river, which flowed along the length of the Malay Basin; it connected the Gulf of Thailand in the north with the South China Sea in the south‐east. The length of the river system (>1200 km long) enables examination of the upstream to downstream controls on the evolution of the incised valley, including sea‐level, climate and tectonics. The valley size, orientation and palaeo‐hydrology suggest close interaction between the regional tectonic framework, low‐angle shelf physiography and a humid‐tropical climatic setting. 相似文献
76.
Abstract Cloudless‐sky solar fluxes calculated by the radiative transfer algorithm used in the Canadian Climate Centre's general circulation climate model are compared with measurements of upwelling radiation at the top of the atmosphere (TOA) and downwelling radiation at the surface. The 12‐layer model partitions the solar spectrum into two broad wavebands (0.25–0.68 and 0.68–4.00 μm). The comparison utilized TOA fluxes estimated from Nimbus‐ 7 measurements and measured downwelling fluxes at the surface for Kalgoorlie, West Australia, and downwelling fluxes at the surface for Woodbridge, Ontario. Model estimates and measurements agreed to within experimental error for most solar zenith angles. Estimates improved, especially at Woodbridge, when aerosol effects were included. The mean bias error was less than 4% for surface irradiance and less than 6% for upwelling TOA irradiance, which produces a TOA albedo error of about 0.01. 相似文献
77.
J. S. Morrill C. M. Korendyke G. E. Brueckner F. Giovane R. A. Howard M. Koomen D. Moses S. P. Plunkett A. Vourlidas E. Esfandiari N. Rich D. Wang A. F. Thernisien P. Lamy A. Llebaria D. Biesecker D. Michels Q. Gong M. Andrews 《Solar physics》2006,233(2):331-372
We present a detailed review of the calibration of the LASCO C3 coronagraph on the SOHO satellite. Most of the calibration
has been in place since early in the mission and has been utilized to varying degrees as required by specific analysis efforts.
However, using observational data from the nearly decade-long database of LASCO images, we have re-evaluated and improved
many aspects of the calibration. This includes the photometric calibration, vignetting function, geometric distortion, stray
light, and exposure and observation times. Using this comprehensive set of corrections we have generated and made available
a set of calibrated coronal images along with a set of periodic background images to ease the accessibility and use of the
LASCO database.
Deceased 相似文献
78.
UNESCO World Heritage status is the highest honour that may be bestowed on a palaeontological site. In addition to heightening conservation status, it confers international recognition of a locality's 'outstanding universal value' and often triggers the release of substantial regional development funds. Despite these incentives it is, perhaps, not surprising that only a handful of fossil sites have successfully navigated the World Heritage selection process. In this feature, we draw on our recent experience of developing a World Heritage bid for the Pennsylvanian 'Coal Age' locality of Joggins, Nova Scotia. As well as demonstrating the huge significance of Joggins, we hope that our findings will provide valuable guidelines for the assessment of World Heritage fossil sites in general. 相似文献
79.
We study sudden brightenings of coronal loops that interconnect active regions. Such brightenings often occur within one or two days after the birth of a new interconnecting loop, as well as in some old interconnections. The brightenings of young loops are obviously associated with the emergence of new magnetic flux near their footpoints, whereas some enhancements of old loops may be triggered by slowly moving disturbances propagating from other centers of activity. A few loop brightenings are associated with flares, but the loop does not brighten in consequence of energy supply from the flare. Both the flare and the loop brightening are independent consequences of one common agent, presumably newly emerging flux.Temperatures in brightened loops are between 3 and 4 × 106 K and densities are < 2 × 109 cm–3, probably < 5 × 108 cm–3 in some old loops. The top part of a loop is the site of the most intense brightening in the initial phase of a loop enhancement. The most frequent lifetime of these brightenings is 6 to 7 hr.Hale Observatories are operated jointly by the Carnegie Institution of Washington and the California Institute of Technology. 相似文献
80.
The observation of a strong seasonal variation of arsenic species found in the estuaries of the Rivers Beaulieu, Test and Itchen in central southern England is presented. The implications of such observations regarding the environmental biomethylation and fate of arsenic in natural waters are also discussed. 相似文献