Structure in the solar corona from radio scintillation measurements     

Richard Woo 《Astrophysics and Space Science》1996,243(1):97-104

Since the 1950s, a wide variety of radio observations based on scattering by electron density fluctuations in the solar wind has provided much of our information on density fluctuations and solar wind speed near the source region of the solar wind. This paper reviews recent progress in the understanding of the nature of these density fluctuations and their relationship to features on the Sun. The results include the first measurements of fine-scale structure within coronal streamers and evidence for structure in solar wind speed in the inner corona.  相似文献   

Solar-planetary cycles in Jupiter's great red spot darkness     

I. Liritzis  B. Petropoulos  C. Banos  E. Sarris 《Earth, Moon, and Planets》1996,73(2):167-179

The change in the darkness of the Great Red Spot (GRS) of Jupiter (1894–1974) has been analysed with Fourier (FFT), Maximum Entropy and Power spectrum (Blackman-Tukey window) (PSA) methods of spectrum analysis. Significance, non-randomness and stationarity tests assigned high variance to periodicities of 33 ± 4, 13–15, about 11, 9 and 3 yrs. The highest correlation between solar activity and GRS darkness was found for the 14th and 16th solar cycle. The periodicities obtained are interpreted as the combined eftects of solar activity, planetary resonances and internal jovian mechanisms.  相似文献   

Brief description of bare essentials of surface transfer and results from simulations with the HAPEX-MOBILHY data     

A. J. Pitman  C. E. Desborough 《Global and Planetary Change》1996,13(1-4)

The Bare Essentials of Surface Transfer (BEST) land surface scheme is briefly described and the key physical parameterisations discussed. Results are then presented to illustrate how the model performs, with forcing data for HAPEX-MOBILHY, compared to a series of other schemes in the simulation of evaporation and sensible heat. The implications of the models performance, and some indications of the future development of the scheme are provided. The basic version of BEST was found to overestimate evaporation for the HAPEX-MOBILHY data, simulating 816 mm yr⁻¹ compared to a range of 550 to 816 mm yr⁻¹ for all models. A modification to the β parameterisation reduced the evaporation to 759 mm yr⁻¹ which, although an improvement, is still probably too high.  相似文献   

What Drives Star Formation?     

Richard M. Crutcher 《Astrophysics and Space Science》2004,292(1-4):225-237

Current theoretical models for what drives star formation (especially low-mass star formation) are: (1) magnetic support of self-gravitating clouds with ambipolar diffusion removing support in cores and triggering collapse and (2) compressible turbulence forming self-gravitating clumps that collapse as soon as the turbulent cascade produces insufficient turbulent support. Observations of magnetic fields can distinguish between these two models because of different predictions in three areas: (1) magnetic field morphology, (2) the scaling of field strength with density and non-thermal velocities, and (3) the mass to magnetic flux ratio, M/Φ. We first discuss the techniques and limitations of methods for observing magnetic fields in star formation regions, then describe results for the L1544 prestellar core as an exemplar of the observational results. Application of the three tests leads to the following conclusions. The observational data show that both magnetic fields and turbulence are important in molecular cloud physics. Field lines are generally regular rather than chaotic, implying strong field strengths. But fields are not aligned with the minor axes of oblate spheroidal clouds, suggesting that turbulence is important. Field strengths appear to scale with non-thermal velocity widths, suggesting a significant turbulent support of clouds. Giant Molecular Clouds (GMCs) require mass accumulation over sufficiently large volumes that they would likely have an approximately critical M/Φ. Yet H I clouds are observed to be highly subcritical. If self-gravitating (molecular) clouds form with the subcritical M/Φ of H I clouds, the molecular clouds will be subcritical. However, the observations of molecular cloud cores suggest that they are approximately critical, with no direct evidence for subcritical molecular clouds or cloud envelopes. Hence, the observations remain inconclusive in deciding between the two extreme-case models of what drives star formation. What is needed to further advance our understanding of the role of magnetic fields in the star formation process are additional high sensitivity surveys of magnetic field strengths and other cloud properties in order to further refine the assessment of the importance of magnetic fields in molecular cores and envelopes.  相似文献   

A deep Chandra survey of the Groth Strip – I. The X-ray data     

K. Nandra  E. S. Laird  K. Adelberger  Jonathan P. Gardner  R. F. Mushotzky  J. Rhodes  C. C. Steidel  H. I. Teplitz  K. A. Arnaud 《Monthly notices of the Royal Astronomical Society》2005,356(2):568-586

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The Dergaon (H5) chondrite: Fall,classification, petrological and chemical characteristics,cosmogenic effects,and noble gas records   总被引：1，自引：0，他引：1  

P. N. SHUKLA  A. D. SHUKLA  V. K. RAI  S. V. S. MURTY  N. BHANDARI  J. N. GOSWAMI  A. C. MAZUMDAR  P. PHUKON  K. DUORAH  R. E. GREENWOOD  I. A. FRANCHI 《Meteoritics & planetary science》2005,40(4):627-637

Abstract— A multiple fall of a stony meteorite occurred near the town of Dergaon in Assam, India, on March 2, 2001. Several fragments weighing <2 kg and a single large fragment weighing ～10 kg were recovered from the strewn field, which extended over several tens of square kilometers. Chemical, petrographic, and oxygen isotopic studies indicate it to be, in most aspects, a typical H5 chondrite, except the unusually low K content of ～340 ppm. A cosmic ray exposure of 9.7 Ma is inferred from the cosmogenic noble gas records. Activities of eleven cosmogenic radionuclides were measured. ²⁶Al and ²²Na activities as well as the ²²Na/²⁶Al activity ratio are close to the values expected on the basis of solar modulation of galactic cosmic rays. The low ⁶⁰Co activity (<1 dpm/kg) is indicative of a small preatmospheric size of the meteorite. Cosmic ray heavy nuclei track densities in olivine grains range from ～106 cm^?2 in samples from the largest fragment to approximately (4–9) × 105 cm^?2 in one of the smaller fragments. The combined track, radionuclide, and noble gas data suggest a preatmospheric radius of ～20 cm for the Dergaon meteorite.  相似文献   

Flows in clumpy planetary nebulae     

T. W. Hartquist  J. E. Dyson 《Astrophysics and Space Science》1996,245(2):263-273

The dynamics of clumps observed in planetary nebulae are considered. The possibility that SiO maser spots in evolved stars and the planetary nebula clumps are formed by the Parker instability behind shocks in pulsating stars' atmospheres is raised. Molecular observations of the clumps are suggested. The effects of the ablation of clumps on the global flow structure of a more tenuous plasma in which they are embedded are reviewed.  相似文献   

Tidal effects on temperature front in the Yellow Sea   总被引：5，自引：0，他引：5  

Ma Jian  Qiao Fangli  Xia Changshui  Yang Yongzeng 《中国海洋湖沼学报》2004,22(3):314-321

Temperature front (TF) is one of the important features in the Yellow Sea, which forms in spring, thrives in summer, and fades in autumn as thermocline declines. TF intensity ⋎S _T ⋎ is defined to describe the distribution of TF. Based on the MASNUM wave-tide-circulation coupled model, temperature distribution in the Yellow Sea was simulated with and without tidal effects. Along 36°N, distribution of TF from the simulated results are compared with the observations, and a quantitative analysis is introduced to evaluate the tidal effects on the forming and maintaining processes of the TF. Tidal mixing and the circulation structure adapting to it are the main causes of the TF. Supported by the National Basic Research Program of China (No. G1999043809) and the National Science Foundation of China (No. 49736190).  相似文献   

Optical properties of solid and liquid sulfur at visible and infrared wavelengths     

R. Sasson  R. Wright  E.T. Arakawa  B.N. Khare  Carl Sagan 《Icarus》1985,64(3):368-374

Knowledge of the optical constants of elemental sulfur has potential applications to Venus, Jupiter, Io, Amalthea, and the Earth. The real part, n, of the index of refraction of liquid sulfur (at 133°C) and of solid orthorhombic sulfur (at 25°C) for the wavelength range 0.4–2.0 μm were measured ellipsometrically. The imaginary part, k, of the refractive index of liquid sulfur was obtained by transmittance measurements at the same temperature and wavelength range. The reflectance of semi-infinite slabs of solid and liquid sulfur is calculated using the measured n and k values. We confirm that sulfur melts on Io would be classified as “black” by the Voyager imaging system.  相似文献   

Gravitational wave radiation from the coalescence of white dwarfs     

P. Lorén-Aguilar  J. Guerrero  J. Isern  J. A. Lobo  E. García-Berro 《Monthly notices of the Royal Astronomical Society》2005,356(2):627-636

We compute the emission of gravitational radiation from the merging of a close white dwarf binary system. This is done for a wide range of masses and compositions of the white dwarfs, ranging from mergers involving two He white dwarfs, through mergers in which two CO white dwarfs coalesce, to mergers in which a massive ONe white dwarf is involved. In doing so we follow the evolution of the binary system using a smoothed particle hydrodynamics code. Even though the coalescence process of the white dwarfs involves considerable masses, moving at relatively high velocities with a high degree of asymmetry we find that the signature of the merger is not very strong. In fact, the most prominent feature of the coalescence is that in a relatively small time-scale (of the order of the period of the last stable orbit, typically a few minutes) the sources stop emitting gravitational waves. We also discuss the possible implications of our calculations for the detection of the coalescence within the framework of future space-borne interferometers like LISA.  相似文献