The rotation period of Neptune's upper atmosphere     

R.Hamilton Brown  Dale P. Cruikshank  Alan T. Tokunaga 《Icarus》1981,47(2):159-165

Significant variations in the near-infrared brightness of Neptune during July and August 1980 were observed. These observations show a well-defined, large-amplitude variation in Neptune's J-K color, with a period of 17.73 ± 0.1 hr and are interpreted as diurnal variations resulting from the 17.73-hr rotation period of the upper atmosphere of Neptune in the presence of inhomogeneous weather. These results qualitatively corroborate those of D. P. Cruikshank (1978, Astrophys. J.220, L57-L59) in an earlier study using similar techniques. In addition, variations were observed in the 5-μm spectral region which are in phase with the variations seen at shorter wavelengths. A new 5-μm measurement of Uranus is also reported.  相似文献   

The phosphine abundance on Saturn derived from new 10-micrometer spectra     

A.T. Tokunaga  H.L. Dinerstein  D.F. Lester  D.M. Rank 《Icarus》1980,42(1):79-85

Spectra of Saturn in the spectral region 10.0–10.7 μm are presented which confirm the presence of PH₃. Comparison to synthetic spectra indicates a PH₃ mixing ratio of at least 2 × 10^?6. No spectral features due to NH₃ or C₂H₄ were observed.  相似文献   

The dust coma of Comet P/Giacobini-Zinner in the infrared     

Hanner MS  Veeder GJ  Tokunaga AT 《The Astronomical journal》1992,104(1):386-393

We present 1-20 micrometers photometry of P/Giacobini-Zinner obtained at the NASA Infrared Telescope Facility, during 1985 June-September (r = 1.57-1.03 AU). A broad, weak 10 micrometers silicate emission feature was detected on August 26.6; a similar weak emission feature could have been hidden in the broadband photometry on other dates. The total scattering and emitting cross section of dust in the inner coma was similar to that in other short-period comets, but a factor of 10 (r = 1.56 AU) to 100 (r = 1.03 AU) lower than the amount of dust in Comet Halley. The thermal emission continuum can be fit with models weighted toward either small or large absorbing grains. The dust production rate near perihelion was approximately 10(5) g/s (small-grain model) to approximately 10(6) g/s (large-grain model). The corresponding dust/gas mass ratio on August 26 was approximately 0.1-1. A silicate-rich heterogeneous grain model with an excess of large particles is compatible with the observed spectrum of Giacobini-Zinner on August 26. Thus, weak or absent silicate emission does not necessarily imply an absence of silicates in the dust, although the abundance of silicate particles < or = 1 micrometer radius must have been lower than in Comet Halley.  相似文献   

Characterization of bottom sediments from Osaka Bay,Japan     

S. Tokunaga  A. Hoshika  H. Tatsumoto 《Environmental Geology》1995,25(4):263-269

The physical, chemical, and dewatering characteristics of 19 bottom sediments from Osaka Bay, Japan, have been analyzed to aid in the development of sediments in the coastal bay area. The sediments in the east near Osaka Port were highly polluted from the influence of human activities and were difficult to dewater. These sediments were composed of fine particles, low in pH, zetapotential, and initial settling rate, and were high in ignition loss, metal concentrations, compression volume, specific resistance, cake water content, and drying index. However, the sediments near Akashi Channel showed the reverse where they are affected by strong tidal current. A correlation analysis has been made of all the parameters. There are significant relationships between all the dewatering parameters. Therefore, sediments difficult to dewater by gravity settling are also difficult to dewater by vacuum filtration and solar evaporation. Sediments containing fine particles and pollutants are difficult to dewater. Several forms of pollutants can occur in the sediments.  相似文献   

Spatially resolved infrared observations of Saturn: I. Equatorial limb scans at 20 μm     

John Caldwell  F.C. Gillett  I.G. Nolt  A. Tokunaga 《Icarus》1978,35(3):308-312

Drift scans of the equator of Saturn have been obtained through narrow band filters at 17.8, 19.7, and 22.7 μm. Spatial resolution was ?17% of the equatorial diameter. These observations clearly differentiate otherwise tenable atmospheric models. A published model by A. Tokunaga and R.D. Cess [Icarus32, 321–327 (1977)] is shown to represent these new observations significantly better than other models from the literature.  相似文献   

Spatially resolved infrared observations of Saturn II. The temperature enhancement at the South pole of Saturn     

A.T. Tokunaga  J. Caldwell  F.C. Gillett  I.G. Nolt 《Icarus》1978,36(2):216-222

North-South scans of Saturn at 17.8, 19.7, and 22.7 μm show enhanced emission from the South polar region. This effect is consistent with the polar brightening observed in the 12 μm ethane band (Gillett and Orton, 1975; Rieke, 1975), and it indicates that the temperature inversion is hotter at the South pole than at the equator. A model for the temperature inversion of the South pole is constructed and compared to the observations.  相似文献   

Spatial and temporal changes in flood hazard potential at coastal lowland area: a case study in the Kujukuri Plain,Japan     

Huali Chen  Yuka Ito  Marie Sawamukai  Tao Su  Tomochika Tokunaga 《Natural Hazards》2016,84(3):1513-1527

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Development of a thin diatom layer observed in a stratified embayment in Japan     

Goh Onitsuka  Yutaka Yoshikawa  Tomoyuki Shikata  Kei Yufu  Kazuo Abe  Takahisa Tokunaga  Katsunori Kimoto  Takeshi Matsuno 《Journal of Oceanography》2018,74(4):351-365

The temporal evolution of a thin phytoplankton layer was observed by field measurements using a research vessel and mooring instruments in the Yatsushiro Sea, a semi-enclosed narrow embayment in Japan, in early August 2013. The subsurface chlorophyll maximum developed into a thin layer within 2 days just below the pycnocline at around 10-m depth, where turbulent mixing (the dissipation rate of turbulent kinetic energy) was weak (low). The layer persisted for 1.5 to 2 days and declined after irradiance drastically decreased at the sea surface. At the peak period, the layer thickness, which is defined as the full-width at half-maximum of the peak in chlorophyll a concentration, ranged from 0.6 to 1.4 m, and the maximum concentration reached 42.3 mg m^?3. The horizontal extent of the layer was approximately 10 km along the longitudinal axis of the bay. The phytoplankton population characterized by the layer was dominated by a chain-forming centric diatom, Chaetoceros spp. The formation mechanisms of the thin diatom layer were investigated using the observed data and a vertical one-dimensional model that includes physical and biological processes. The results suggest that the development of the thin layer was caused by in situ growth and aggregation due to nutrient-dependent sinking of the species under weak turbulence. The study highlights that continuous multidisciplinary observations and understanding species-specific physiological responses to environmental variations are necessary to elucidate drastically fluctuating phytoplankton dynamics in a coastal water.  相似文献   

Physical properties of the shallow sediments in late Pleistocene formations,Ursa Basin,Gulf of Mexico,and their implications for generation and preservation of shallow overpressures     

N.T.T. Binh  T. Tokunaga  T. Nakamura  K. Kozumi  M. Nakajima  M. Kubota  H. Kameya  M. Taniue 《Marine and Petroleum Geology》2009

Understanding the evolution of abnormally high fluid pressures within sedimentary formations is critical for analysing hydrogeological processes and assessing drilling risks. We have constructed a two-dimensional basin model and have performed numerical simulations to increase the understanding of the history of fluid flow and shallow overpressures in the Pleistocene and Holocene formations in the Ursa basin, deepwater Gulf of Mexico. We measured physical properties of sediments, such as porosity and permeability, in the laboratory and estimated in situ pore pressures from preconsolidation pressures. We obtained porosity–effective stress relationships from measurements of bulk density, grain density and preconsolidation pressures in the laboratory. Porosity–effective stress relationships were also obtained from downhole density logs and measured pore pressures. The porosity–effective stress and porosity–permeability relationships obtained were applied in two-dimensional basin simulations. Results showed that high pore pressures developed shortly after sediment deposition. Peaks in pore pressure ratios were related to high sedimentation rates of mass transport deposits and the incision of the Ursa channel. Lateral flows from the area where the overburden is thick towards the area where it is thin have occurred at least since 30 ka. Present pore pressure and temperature distributions suggest that lateral flows play a role in re-distributing heat in the basin.  相似文献   

Infrared spectroscopy of crystalline and amorphous diacetylene (C₄H₂) and implications for Titan's atmospheric composition     

Li Zhou  Ralf I. Kaiser  Alan T. Tokunaga 《Planetary and Space Science》2009,57(7):830-3003

New laboratory spectra of crystalline and amorphous diacetylene ice have been recorded in the range of 7000-500 cm⁻¹ (1.4-20 μm) to aid in the identification of solid diacetylene on Saturn's moon Titan. We have established that amorphous diacetylene ice is stable only at temperatures less than 70±1 K. With respect to observations on Titan, the best approach would be to utilize future space-based telescopes to search for the ν₄ (3277/3271 cm⁻¹) in absorption against the reflected light from the sun and the slightly weaker ν₈ absorption bands (676/661 cm⁻¹) in absorption against the continuum emission.  相似文献