The Gas Production Rate and Coma Structure of Comet C/1995 O1 (Hale–Bopp)     

Morgenthaler  Jeffrey P.  Harris  Walter M.  Roesler  Frederick L.  Scherb  Frank  Anderson  Christopher M.  Doane  Nathaniel E.  Oliversen  Ronald J. 《Earth, Moon, and Planets》2002,90(1-4):77-87

The University of Wisconsin–Madison and NASA–Goddard conducted acomprehensive multi-wavelength observing campaign of coma emissionsfrom comet Hale–Bopp, including OH 3080 Å, [O I] 6300 Å H₂O⁺ 6158 Å, H Balmer-α 6563 Å, NH₂ 6330 Å, [C I] 9850 ÅCN 3879 Å, C₂ 5141 Å, C₃ 4062 Å,C I 1657 Å, and the UV and optical continua. In thiswork, we concentrate on the results of the H₂O daughter studies.Our wide-field OH 3080 Å measured flux agrees with other, similarobservations and the expected value calculated from published waterproduction rates using standard H₂O and OH photochemistry.However, the total [O I] 6300 Å flux determined spectroscopically overa similar field-of-view was a factor of 3-4 higher than expected.Narrow-band [O I] images show this excess came from beyond theH₂O scale length, suggesting either a previously unknown source of[O I] or an error in the standard OH + ν→ O(¹ D) + H branching ratio. The Hale–Bopp OH and[O I] distributions, both of which were imaged tocometocentric distances >1 × 10⁶ km, were more spatiallyextended than those of comet Halley (after correcting for brightnessdifferences), suggesting a higher bulk outflow velocity. Evidence ofthe driving mechanism for this outflow is found in the Hα lineprofile, which was narrower than in comet Halley (though likelybecause of opacity effects, not as narrow as predicted by Monte-Carlomodels). This is consistent with greater collisional coupling betweenthe suprathermal H photodissociation products and Hale–Bopp's densecoma. Presumably because of mass loading of the solar wind by ionsand ions by the neutrals, the measured acceleration of H₂O⁺ downthe ion tail was much smaller than in comet Halley. Tailwardextensions in the azimuthal distributions of OH 3080 Å,[O I], and [C I] , as well as a Doppler asymmetry in the[O I] line profile, suggest ion-neutral coupling. While thetailward extension in the OH can be explained by increased neutralacceleration, the [O I] 6300 Å and [C I] 9850 Å emissions show 13%and >200% excesses in this direction (respectively), suggesting anon-negligible contribution from dissociative recombination of CO⁺and/or electron collisional excitation. Thus, models including theeffects of photo- and collisional chemistry are necessary for the fullinterpretation of these data.  相似文献   

Thermal behavior of horizontally mixed surfaces on Mars     

Nathaniel E. Putzig  Michael T. Mellon 《Icarus》2007,191(1):52-67

Current methods for deriving thermal inertia from spacecraft observations of planetary brightness temperature generally assume that surface properties are uniform for any given observation or co-located set of observations. As a result of this assumption and the nonlinear relationship between temperature and thermal inertia, sub-pixel horizontal heterogeneity may yield different apparent thermal inertia at different times of day or seasons. We examine the effects of horizontal heterogeneity on Mars by modeling the thermal behavior of various idealized mixed surfaces containing differing proportions of either dust, sand, duricrust, and rock or slope facets at different angles and azimuths. Latitudinal effects on mixed-surface thermal behavior are also investigated. We find large (several 100 J m⁻² K⁻¹ s^−1/2) diurnal and seasonal variations in apparent thermal inertia even for small (∼10%) admixtures of materials with moderately contrasting thermal properties or slope angles. Together with similar results for layered surfaces [Mellon, M.T., Putzig, N.E., 2007. Lunar Planet. Sci. XXXVIII. Abstract 2184], this work shows that the effects of heterogeneity on the thermal behavior of the martian surface are substantial and may be expected to result in large variations in apparent thermal inertia as derived from spacecraft instruments. While our results caution against the over-interpretation of thermal inertia taken from median or average maps or derived from single temperature measurements, they also suggest the possibility of using a suite of apparent thermal inertia values derived from single observations over a range of times of day and seasons to constrain the heterogeneity of the martian surface.  相似文献   

A system’s approach to assess the exposure of agricultural production to climate change and variability     

Aavudai Anandhi  Jean L. Steiner  Nathaniel Bailey 《Climatic change》2016,136(3-4):647-659

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A simple variational approach to refraction and related problems in geodesy     

Nathaniel Grossman 《Journal of Geodesy》1975,49(3):217-240

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Suivis temporels comparés de la structure thermique d'eaux côtières libanaises (Batroun) et françaises (Marseille) entre juin 1999 et octobre 2002     

Marie Abboud-Abi Saab  Jean-Claude Romano  Nathaniel Bensoussan  Milad Fakhri 《Comptes Rendus Geoscience》2004,336(15):1379-1390

Vertical temperature profiles were recorded from June 1999 to October 2002 (at least once a month) at two Mediterranean sites, in the eastern basin (Batroun, Lebanon; 0–100 m) and in the northwestern basin (Marseilles, France; 0–55 m). At the two sites, the thermal seasonal evolution and the thermocline time dynamics are quite identical. But in the Lebanese waters, at comparable water depths, temperatures are currently 4 to 5?°C higher than in the French waters, the thermocline is longer (more than 6 months), permanent and deeper (40–50 m) than in Marseilles (20–30 m). The latter frequently disappears in summer due to northwest winds inducing cold waters. This is principally due to differences in prevailing wind regimes at each site. Such evaluation, coupled with long-term observations of temporal evolution of coastal water at the regional level of the Mediterranean basins, will shed light on temperature regime fluctuations and their consequences in the context of global warming of the Mediterranean. To cite this article: M. Abboud-Abi Saab et al., C. R. Geoscience 336 (2004).  相似文献   

Methods of terrain evaluation,Mackenzie Transportation Corridor,N.W.T., Canada     

Nathaniel W. Rutter 《地球表面变化过程与地形》1977,2(4):295-308

In 1971 and 1972, the Terrain Sciences Division of the Geological Survey of Canada carried out the largest mapping program in its history of the distribution and characteristics of terrain types. Over 140.000 mile² (360,000 km²) of the Mackenzie Transportation Corridor was evaluated. This information was supplied to the public, industry and government in order to plan and design projects properly, by efficiently utilizing natural resources and minimizing environmental damage. The requirements of potential users varied to such a degree that it was decided to map the ‘basic’ geology and other terrain characteristics so that derivative maps could be constructed for specific uses. A mapping system was devised for surficial deposits using genesis as the primary unit, modified by texture and morphology. Organic and permafrost terrain were included, factors not ordinarily a part of traditional geological mapping. The system was comprehensive and flexible enough to include such aspects as the percentages of minor units, unit thickness, and slope and other morphological characteristics. In bedrock and unglaciated areas, a second system based upon the same principles as the first but arranged in a different manner was devised. In this case, the primary unit is based upon relief, with additional information on lithology of the bedrock, texture of overlying debris, and broad morphological and slope characteristics. Comprehensive legends were prepared. Using the mapping units as the base, the legends were divided into various categories, providing information on the composition, ground ice content, thickness, and engineering characteristics of the deposits, and surface characteristics including topography, drainage pattern, vegetation, and dominant soils (pedologic sense).  相似文献   

Calibration of the in situ cosmogenic 14C production rate in New Zealand's Southern Alps     

Irene Schimmelpfennig  Joerg M. Schaefer  Brent M. Goehring  Nathaniel Lifton  Aaron E. Putnam  David J. A. Barrell 《第四纪科学杂志》2012,27(7):671-674

In situ cosmogenic ¹⁴C (in situ ¹⁴C) analysis from quartz‐bearing rocks is a novel isotopic tool useful for quantifying recent surface exposure histories (up to ～25 ka). It is particularly powerful when combined with longer‐lived cosmogenic isotopes such as ¹⁰Be. Recent advances in the extraction of in situ ¹⁴C from quartz now permit the routine application of this method. However, only a few experiments to calibrate the production rate of in situ ¹⁴C in quartz have been published to date. Here, we present a new in situ ¹⁴C production rate estimate derived from a well‐dated debris flow deposit in the Southern Alps, New Zealand, previously used to calibrate ¹⁰Be production rates. For example, based on a geomagnetic implementation of the Lal/Stone scaling scheme we derive a spallogenic production rate of 11.4 ± 0.9 atoms ¹⁴C (g quartz)^?1 a^?1 and a ¹⁴C/¹⁰Be spallogenic production rate ratio of 3.0 ± 0.2. The results are comparable with production rates from previous calibrations in the northern hemisphere. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Predicting surf zone injuries along the Delaware coast using a Bayesian network     

Doelp  Matthew B.  Puleo  Jack A.  Plant  Nathaniel G. 《Natural Hazards》2019,98(2):379-401

Natural Hazards - More than 2000 surf zone injury (SZI) events, including 196 spinal injuries and 6 fatalities, were recorded at the five most populated beaches along the 25 miles of...  相似文献   

Benefits of design modifications to the Birkbeck bedload sampler illustrated by flash‐floods in an ephemeral gravel‐bed channel     

Nathaniel Bergman  Jonathan B. Laronne  Ian Reid 《地球表面变化过程与地形》2007,32(2):317-328

The benefits of three simple modifications to the design of a Birkbeck bedload slot‐sampling system that has been continuously operating in Nahal Eshtemoa, Israel, since the early 1990s are demonstrated. The modifications include the deployment of a removable slot cover which delays the accumulation of sediment, so allowing sampling at late stages of a flood and, in conjunction with other samplers, extending the period of sampling during a flood wave; inclusion of a slot the size of which is adjustable so that that the probability of sampling the largest clast sizes in transit as bedload can be increased post‐installation, once knowledge is gained about the bedload grain‐size distribution; and a sampler side‐wall door that allows stratification and textural changes within the accumulated bedload to be identified, so promoting intelligent sampling of the deposit for grain‐size determination. Results from seven flash‐floods are presented and discussed, with recommendations for bedload monitoring, particularly in rivers where sediment flux is high and dynamic sediment records are inevitably short because of instrumental limitations. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

A Bayesian approach to calibrating period-luminosity relations of RR Lyrae stars in the mid-infrared     

Christopher R. Klein  Joseph W. Richards  Nathaniel R. Butler  Joshua S. Bloom 《Astrophysics and Space Science》2012,341(1):83-87

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