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1.
An investigation of low-resolution ratio spectra of Jupiter, Saturn, and Titan in the region 5400–6500 Å has permitted new evaluations of ammonia absorption bands. The distribution of ammonia over the disk of Jupiter is very inhomogeneous. The carbon-to-nitrogen ratio is distinctly different from the solar value, but this is probably a result of uneven mixing of methane and ammonia, as suggested previously by Kuiper, rather than a compositional anomaly. The abundance of ammonia on Saturn also shows spatial variations, but appears constant in time over a 3-yr period. Two weak, unidentified absorptions were discovered in the red region of Titan's spectrum, in the absence of any detectable ammonia. The new upper limit is ηN < 120 cm-am. 相似文献
2.
We present, for the first time, the main sources of sporadic meteors as inferred from meteor-head echoes obtained by a high-power large-aperture radar (HPLAR). Such results have been obtained at the Jicamarca HPLAR (11.95° S, 76.87° W, 1° dip angle). Observations are based on close to 170,000 meteors detected in less than 90 h spread over 14 days, between November 2001 and February 2006. Meteors with solar orbits are observed to come from basically six previously known sources, i.e., North and South Apex, Helion, Anti-Helion, and North and South Toroidal, representing ∼91% of the observations. The other ∼9% represents meteors with observed velocities greater than the Sun's escape velocity at 1 AU, most of them of extra-solar origin. Results are given before and after removing the Earth's velocity and the sources are modeled with two-dimensional Gaussian distributions. In general, our results are in very good agreement with previously known sources reported by Jones and Brown [Jones, J., Brown, P.G., 1993. Mon. Not. R. Astron. Soc. 265, 524-532] using mainly specular meteor radar (SMR) data gathered over many years and different sites. However, we find slightly different locations and widths, that could be explained on the basis of different sensitivities of the two techniques and/or corrections needed to our results. For example, we find that the North and South Apex sources are well defined and composed each of them of two collocated Gaussian distributions, one almost isotropic with ∼10° width and the other very narrow in ecliptic longitude and wide in ecliptic latitude. This is the first time these narrow-width sources are reported. A careful quantitative analysis is needed to be able to compare the strengths of meteor sources as observed with different techniques. We also present speed and initial altitude distributions for selected sources. Using a simple angular sensitivity function of the combined Earth-atmosphere-radar instrument, and an altitude selection criteria, the resulting meteor sources are in better qualitative agreement with the results obtained with SMRs. 相似文献
3.
Ben B. Balsley Dale A. Lawrence Ronald F. Woodman David C. Fritts 《Boundary-Layer Meteorology》2013,147(1):165-178
We report results of preliminary high-resolution in situ atmospheric measurements through the boundary layer and lower atmosphere over the southern coast of Perú. This region of the coast is of particular interest because it lies adjacent to the northern coastal edge of the sub-tropical south-eastern Pacific, a very large area of ocean having a persistent stratus deck located just below the marine boundary layer (MBL) inversion. Typically, the boundary layer in this region during winter is topped by a quasi-permanent, well-defined, and very large temperature gradient. The data presented herein examine fine-scale details of the coastal atmosphere at a point where the edge of this MBL extends over the coastline as a result of persistent onshore flow. Atmospheric data were gathered using a recently-developed in-house constructed, GPS-controlled, micro-autonomous-vehicle aircraft (the DataHawk). Measured quantities include high-resolution profiles of temperature, wind, and turbulence structure from the surface to 1,300 m. 相似文献
4.
3ew spectra of Titan centered at 7500 Å, at resolutions of 4 and 1 Å are presented. Weak absorptions coincident with features observed in the spectra of Uranus and Neptune are found. This observation suggests methane abundances in excess of 1 km-am, thereby emphasizing the complexity of line formation in Titan's atmosphere. The question of the total atmospheric pressure of Titan must be reexamined. 相似文献
5.
Spatially resolved absolute reflectivities of several regions of the Jovian disk in the wavelength region 3000 to 10760 Å are presented. Spectra were obtained of the central meridian and limbs of the Equatorial Region, North Equatorial Belt, and North Tropical Zone. Equivalent widths of several CH4 and NH3 bands are measured. The spatial variations of continuum reflectivity and absorption band profiles are shown in various ratio spectra. 相似文献
6.
Rethinking an old tracer experiment in fractured crystalline rock suggests a concept of groundwater flow in sparse networks of long channels that is supported by results from an innovative lattice network model. The model, HyperConv, can vary the mean length of ‘strings’ of connected bonds, and the gaps between them, using two independent probability functions. It is found that networks of long channels are able to percolate at lower values of (bond) density than networks of short channels. A general relationship between mean channel length, mean gap length and probability of percolation has been developed which incorporates the well-established result for ‘classical’ lattice network models as a special case. Using parameters appropriate to a 4-m diameter drift located 360 m below surface at Stripa Mine Underground Research Laboratory in Sweden, HyperConv is able to reproduce values of apparent positive skin, as observed in the so-called Macropermeability Experiment, but only when mean channel length exceeds 10 m. This implies that such channel systems must cross many fracture intersections without bifurcating. A general relationship in terms of flow dimension is suggested. Some initial investigations using HyperConv show that the commonly observed feature, ‘compartmentalization’, only occurs when channel density is just above the percolation threshold. Such compartments have been observed at Kamaishi Experimental Mine (Japan) implying a sparse flow network. It is suggested that compartments and skin are observable in the field, indicate sparse channel systems, and could form part of site characterization for deep nuclear waste repositories. 相似文献
7.
Analysis of spectroscopic observations of Mars requires values of the effective Martian airmass to obtain true abundances. Semi-arbitrary assumptions for the airmass correction have been used in most of the past publications on the subject. We have computed detailed values corresponding to specified slits superimposed on the disk of the planet, giving useful output in the form of curves presenting the average airmass for different regions of the planet and various conditions of planet diameter, seeing and phase angle. 相似文献
8.
The use of explosives to catch fish has caused extensive damage to coral reefs throughout Southeast Asia, but the frequency with which they are used is largely unknown. The aim of this work is to develop a detection system capable of distinguishing underwater explosions from background noise, and locating their origin by triangulation. Blast signals have been recorded over a range of distances and the key features that differentiate them from background noise have been determined. For small charges the effective range of such a detector is more than 12 km and may extend up to 50 km depending on the mass of the charges being used. Such a system would help to determine the scale of the problem, identify areas at greatest risk and quantify the effectiveness of management intervention designed to control destructive fishing practices. It may assist with fisheries enforcement in some areas. 相似文献
9.
Little is known about the spatial and temporal distribution of blast fishing which hampers enforcement against this activity. We have demonstrated that a triangular array of hydrophones 1 m apart is capable of detecting blast events whilst effectively rejecting other sources of underwater noise such as snapping shrimp and nearby boat propellers. A total of 13 blasts were recorded in Sepangor bay, North of Kota Kinabalu, Sabah, Malaysia from 7th to 15th July 2002 at distances estimated to be up to 20 km, with a directional uncertainty of 0.2 degrees . With such precision, a network of similar hydrophone arrays has potential to locate individual blast events by triangulation to within 30 m at a range of 10 km. 相似文献
10.
Spectrophotometric scans of Mars and the Moon in the region 4000–5000 Å were obtained and ratioed. No evidence of any absorption greater than 3% is visible in the Martian spectrum. Using our own laboratory spectra of NO2 as well as the published work of Hall and Blacet (1952) we confirm Marshall's (1964) upper limit of 8 μm atmospheres (0.0008 cm amagat) for the abundance of NO2 in the atmosphere of Mars. 相似文献