Magnetoacoustic-gravity surface waves     

Alan J. Miles  H. R. Allen  B. Roberts 《Solar physics》1992,141(2):205-234

The linearized theory for the parallel propagation of magnetoacoustic-gravity surface waves is developed for an interface of a horizontal magnetic field above a field-free medium. The media either side of the interface are taken to be isothermal. The dispersion relation is obtained for the case of a constant Alfvén speed. In the absence of gravity the interface may support one or two surface modes, determined by the relative temperatures and magnetism of the two media. The effect of gravity on the modes is examined and dispersion diagrams and eigenfunctions are given. In the usual - k _x diagnostic diagram, the domain of evanescence is shown to be divided into two distinct regions determining whether a given mode will have a decaying or growing vertical velocity component. In the absence of a magnetic field the transcendental dispersion relation may be rewritten as a polynomial. This polynomial possesses two acceptable solutions only one of which may exist in any given circumstances (depending on the ratio of the densities). If the gas density within the field exceeds that in the field-free medium, then the f-mode may propagate. The f-mode exists in a restricted band of horizontal wavenumber and only when the field-free medium is warmer than the magnetic atmosphere. An analytical form for the wave speed of the f-mode is obtained for small values of the Alfvén speed. It is shown that the f-mode is related to the fast magnetoacoustic surface wave, merging into that mode at short wavelengths.  相似文献   

Trace metals in suspended particulate matter and in sediment trap material from a permanently anoxic fjord — Framvaren, South Norway     

Jens M. Skei  Douglas H. Loring  Reijo T. T. Rantala 《Aquatic Geochemistry》1996,2(2):131-147

Geochemical studies of the trace metal concentrations in suspended particulate matter (SPM) and sediment trap material from a permanently anoxic fjord, Framvaren, South Norway in 1989 and 1993 indicate that extremely high concentrations of zinc (max = 183920 mg/kg), copper (max = 4130 mg/kg), lead (max = 2752 mg/kg), and cadmium (max= 8.1 mg/kg) sometimes (1993) occur in the SPM collected in the anoxic water layer. The highest concentrations of Zn occur just below the redoxcline at 22 m water depth (in 1993), and copper, lead and cadmium have maximum concentrations between 30 and 80 m depth, where the amount of total SPM is at a minimum (about 0.3 mg/L). On a mass per volume (g/L) basis, the maximum concentrations of Cd, Cu and Fe occur at the interface (21m) and those of Zn occur just below the redoxcline (22 m depth). The SPM and sediment trap data suggest that the metals are precipitated as sulfide minerals in the anoxic water. The presence of particulate sulfides was confirmed by SEM studies that show the occurrence of discrete metal (Cu, Fe, Pb, and Zn) sulfide particles in size from 10–20 m as well as framboidal pyrites (1–5 m in size). Higher levels of metal sulfides at intermediate depths rather than in the deep water of Framvaren (> 100 m), may be due to input of trace metals by water exchange over the sill in the upper part of the water column. In the deep water, less metal sulfide precipitation takes place due to depletion of trace metals, and the dilution of particulate metal concentrations by organic matter and by the chemogenic formation of calcite.  相似文献   

The Taconite Inlet Lakes Project: a systems approach to paleoclimatic reconstruction     

R. S. Bradley  M. J. Retelle  S. D. Ludlam  D. R. Hardy  B. Zolitschka  S. F. Lamoureux  M. S. V. Douglas 《Journal of Paleolimnology》1996,16(2):97-110

A comprehensive study of meteorological, hydrological, limnological and sedimentological conditions in the watersheds of density-stratified (meromictic) lakes around Taconite Inlet, Northern Ellesmere Island, N.W.T., Canada was carried out from 1990–1992. Lakes C1 and C2 contain seawater trapped by isostatic uplift as the former embayments became isolated from the sea. These lakes, and Lake C3, contain varved sediments which provide an annually resolvable paleoclimatic record. By studing the major systems influencing sedimentation in one of these lakes (Lake C2) a better understanding of the climatic controls on varve formation, and hence on the paleoclimatic signal in the varved sediment record, was obtained. The varves of Lake C2 provide a proxy record of summer temperature for the region.This is the first in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.  相似文献   

Spectral reflectance change and luminescence of selected salts during 2–10 KeV proton bombardment: Implications for Io     

Robert M. Nelson  Douglas B. Nash 《Icarus》1979,39(2):277-285

Radiation damage and luminescence, caused by magnetospheric charged particles, have been suggested by several authors as mechanisms for explaining some of the peculiar spectral/albedo features of Io. We have pursued this possibility by measuring the uv-visual spectral reflectance and luminescent efficiency of several proposed Io surface constituents during 2 to 10-keV proton irradiation at room temperature and at low temperature (120 < T < 140°K). The spectral reflectance of NaCl and KCl during proton irradiation exhibits the well-known F-center absorption bands at 4580 and 5560 Å. Na₂SO₄ shows a generalized darkening which increases toward longer wavelengths. NaNO₃ shows a spectral reflectance change indicative of the partial alteration of NaNo₃ to NaNo₂. NaNO₂ shows no change. The luminescent efficiencies of NaCl and KCl are ～10^?4 at 300°K and increase by one-half order of magnitude at ～130°K. The efficiencies of K₂CO₃, Na₂CO₃, Na₂SO₄, and NaNO₃ are 10^?4, 10^?4, 10^?5 and 10^?6, respectively, at 300°K and they all decrease by one-half order of magnitude at ～130°K. These results indicate that magnetospheric proton irradiation of Io could cause spectral features in its observed ultraviolet and visible reflection spectrum if salts such as those studied here are present on its surface. However, because the magnitude of these spectral effects is dependent on competing factors such as surface temperature, incident particle energy flux, solar bleaching effects, and trace element abundance, we are unable at this time to make a quantitative estimate of the strength of these spectral effects on Io. The luminescent efficiencies of pure samples that we have studied in the laboratory suggest that charged-particle induced luminescence from Io's surface might be observable by a spacecraft such as Voyager when viewing Io's dark side.  相似文献   

High spatial and spectral resolution 10-μm observations of jupiter     

Alan T. Tokunaga  R.F. Knacke  S.T. Ridgway 《Icarus》1980,44(1):93-101

Ten-micrometer spectra of the North Tropical Zone, North Equatorial Belt, and Great Red Spot at a spectral resolution of 1.1 cm^?1 are compared to synthetic spectra. These ground-based spectra were obtained simultaneously with the Voyager 1 encounter with Jupiter in March, 1979. The NH₃ vertical distribution is found to decrease with altitude significantly faster than the saturated vapor pressure curve and is different for the three observed regions. Spatial variability in the NH₃ mixing ratio could be caused by changes in the amount of NH₃ condensation or in the degree of the NH₃ photolysis. The C₂H₆ emission at 12 μm has approximately the same strength at the North Tropical Zone and North Equatorial Belt, but it is 30% weaker at the Great Red Spot. A cooler temperature inversion or a smaller abundance of C₂H₆ could explain the lower C₂H₆ emission over the Great Red Spot.  相似文献   

Measurements of magnetic fluxes and field strengths in the photospheric network     

Theodore D. Tarbell  Alan M. Title 《Solar physics》1977,52(1):13-25

We present digital pictures of an active region network cell in five quantities, measured simultaneously: continuum intensity, line-center intensity, equivalent width, magnetogram signal, and magnetic field strength. These maps are derived from computer analysis of circularly polarized line profiles of FeI 5250.2; spectral and spatial resolution are 1/40 Å and 1.5, respectively. Measured Zeeman splittings show the existence of strong magnetic fields (1000–1800 G) at nearly all points with a magnetogram signal exceeding 125 G. The mean and rms deviation of the field strengths change by less than 20% over a factor-of-four range of fluxes. From the significant disparity between measured fluxes and field strengths, we conclude that large flux patches (up to 4 across) consist of closely-packed unresolved filaments. The smallest filaments must be less than 0.7 in diameter. We also observe the dark component of the photospheric network, which appears to contain sizable transverse fields.  相似文献   

The dark night sky: Donald D. Clayton. Quadrangle/New York Times Book Co., New York, 1975. 206 pp. $9.95     

Alan P. Lightman 《Icarus》1977,30(2):436-437

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Airborne total eclipse observation of the extreme solar limb at 400 μm     

T. Alan Clark  Rita T. Boreiko 《Solar physics》1982,76(1):117-128

The total solar eclipse of February 26, 1979 was monitored at far infrared wavelengths from the NASA Lear Jet Observatory flying at 12.9 km in the eclipse shadow. The resultant eclipse curve for radiation within a bandwidth of 20 cm^–1 centered upon 25 cm^–1 (400 m) was measured and analysed at an equivalent angular resolution of 1 arc sec over a 100 arc sec region adjacent to the limb to provide information on the intensity distribution of continuum radiation close to this limb. The curve has been compared to predictions derived from models of the solar atmosphere for the specific geometry of this eclipse, and is shown to match most closely that derived from a uniform distribution of radiation across the disk. This is in distinct contrast to the result obtained in the only other comparable experiment, carried out over Africa in 1973 from a supersonic Concorde aircraft, in which an intense but narrow spike of far infrared radiation at the extreme solar limb was inferred from the data. The absence also in the present observations of the significant limb brightening predicted by the HSRA model (in which homogeneity within the source region is assumed) is in substantial agreement with lower resolution results from mountain altitudes. This result is interpreted as further evidence for the presence in the Sun's lower chromosphere of significant inhomogeneity with a scale size of at least 1000 km at this depth.  相似文献   

Intercomparison of measurements of stratospheric hydrogen fluoride     

William G. Mankin  M. T. Coffey  K. V. Chance  W. A. Traub  B. Carli  F. Mencaraglia  S. Piccioli  I. G. Nolt  J. V. Radostitz  R. Zander  G. Roland  Douglas W. Johnson  Gerald M. Stokes  C. B. Farmer  R. K. Seals 《Journal of Atmospheric Chemistry》1990,10(2):219-236

Observations of the vertical profile of hydrogen fluoride (HF) vapor in the stratosphere and of the vertical column amounts of HF above certain altitudes were made using a variety of spectroscopic instruments in the 1982 and 1983 Balloon Intercomparison Campaigns. Both emission instruments working in the far infrared spectral region and absorption instruments using solar occultation in the 2.5m region were employed. No systematic differences were seen in results from the two spectral regions. A mean profile from 20–45 km is presented, with uncertainties ranging from 20% to 50%. Total columns measured from ground and from 12 km are consistent with the profile if the mixing ratio for HF is small in the tropophere and low stratosphere.  相似文献   

Solar radio bursts of spectral type II,coronal shocks,and optical coronal transients     

Alan Maxwell  Murray Dryer 《Solar physics》1981,73(2):313-329

The association of solar radio bursts of spectral type II and coronal shocks with solar flare ejecta observed in H, the green coronal line, and white-light coronagraphs is examined. Rather than identifying fast-moving optical coronal transients with outward-travelling shock waves that generate type II radio bursts, as has been suggested in some earlier papers, we suggest that, for the most part, such transients should probably be identified with piston-type phenomena well behind the shock. We then discuss a general model, consisting of three main velocity regimes, in which we relate type II radio bursts and coronal shocks to optically-observed ejecta.  相似文献