绝对重力测量在云南和北京观测到的重力时间变化

中国地震局地震研究所与德国汉诺威大学大地测量研究所于１９９０,１９９２和１９９５年共同在滇西地震预报实验场和昆明进行了３次绝对重力测量。此外,１９９０,１９９２年在北京,１９９０年在武汉也进行了绝对重力测量。通过对各次绝对测量的结果进行比较,并与其它重力仪获得的数据的对比估算了它们的可靠性,进而详细地讨论了各个测点的重力变化。     

A dense bottom water plume in the western Barents Sea: downstream modification and interannual variability

The generation and downstream modification of a cold dense Arctic shelf water plume were studied with moored current meters, thermistor chains and conductivity/temperature sensors deployed from August 1993 to September 1994 south of the Storfjord in the Svalbard Archipelago. These observations are compared to similar time series from 1991/92. In 1993/94, bottom water with temperatures close to the freezing point drained continuously from Storfjord between March and September with a mean speed of 0.14 m s⁻¹. About 1.5 months after the plume front had left the Storfjord, it reached the shelf break, 150 km away. The plume had increased its width from 15 km to about 35 km, but its thickness of 50 m remained almost constant and it left the shelf edge at a similar speed. The increased volume transport and the change of temperature/salinity properties indicate an entrainment of 110% of ambient Atlantic water into the plume on its way from the production area to the shelf edge.The maximum salinity of the cold plume was 0.2 lower in 1993/94 than in 1991/92, whilst the temperature/salinity-range of the surrounding Atlantic water remained unchanged. Probably as a dynamic consequence, the speed of the plume was considerably lower in 1993/94. The lower salinity of the plume in 1993/94 is a result of both the 30% less ice formation in Storfjord, caused by lower heat flux and less open water, and a lower surface salinity at the beginning of ice formation. During 1993/94, the Storfjord plume was too light to sink below 700 m.     

Hydrodynamics of hypersonic jets: experiments and numerical simulations

Stars form in regions of the galaxy that are denser and cooler than the mean interstellar medium. These regions are called Giant Molecular Clouds. At the beginning of their life, up to 10⁵–10⁶ years, stars accrete matter from their rich surrounding environment and are origin of a peculiar phenomenon that is the jet emission. Jets from Young Stellar Objects (YSOs) are intensively studied by the astrophysical community by observations at different wavelengths, analytical and numerical modeling and laboratory experiments. Indications about the jet propagation and its resulting morphologies are here obtained by means of a combined study of hypersonic jets carried out both in the laboratory and by numerical simulations.     

Interplanetary dust detected by the Cassini CDA Chemical Analyser

During its cruise phase, prior to encountering Jupiter, the Cosmic Dust Analyser (CDA) onboard the Cassini spacecraft returned time of flight mass spectra (TOF MS) of two interplanetary dust particles. Both particles were found to be iron-rich, with possible traces of hydrogen, carbon, nickel, chromium, manganese, titanium, vanadium and minor silicates. Carbon, hydrogen, oxygen and potassium are also present as possible contaminants of the impact target of CDA. Silicates and magnesium do not feature predominantly in the spectra; this is surprising considering the expected dominance of silicate-rich minerals in interplanetary dust particles. The particle masses are and . The corresponding radii ranges for the particles, assuming densities from 7874-2500 kg m⁻³ are 0.7-4 μm and 2.6-6.8 μm, respectively. With the same density assumptions the β values (ratio of radiation pressure to gravitational force) are estimated as 0.027-0.21 and 0.016-0.06 respectively, allowing possible orbits to be calculated. The resulting orbits are bound and prograde with semi-major axes, eccentricities and inclinations in the region of 0.3-1.26 AU, 0.4-1.0 and 0-60° for the first particle and 0.8-2.5 AU, 0.2-0.9 and 0-30° for the second. The more probable orbits within these ranges indicate that the first particle is in an Aten-like orbit, whilst the second particle is in an Apollo-like orbit, despite both grains having very similar, predominantly metallic compositions. Other possible orbital solutions for both particles encompass orbits which more closely resemble those of Jupiter-family comets.     

Validation of boundary layer parameters of climate model REMO: estimation of leaf area index from NOAA-AVHRR data for the Baltimos region

The preparation of time- and space-dependent input surface parameters for the climate model REMO was one task of the Baltimos project “Validation of Boundary Layer Parameters and Extension of Boundary conditions of Climate Model REMO”. The leaf area index (LAI) is one of these parameters. It is used in REMO as defined value per month for each land-use class with a defined seasonal trend during the year. Since 1982 at the Institute of Meteorology of the Free University Berlin, a high-resolved AVHRR data set of the NOAA satellite has been available (1/100 degree, approximately 1?×?1 km at nadir in a geographic coordination system) (Koslowsky 1996). The vegetation periods of the years 1997 until 2001 were selected from the dataset to estimate the LAI within the Baltimos region on the basis of an algorithm by Sellers et al. (J Climate 9:706–737, 1996) and a modified United States Geological Survey (USGS) land-use classification. The calculated high-resolved NOAA LAI values were converted to the 1/6 degree grid of the REMO climate model. Then, they were compared to the fixed LAI values, which are used in the model.     

Temperature-sensitive line ratios of the lithium-like ion O vi

During the past decade a number of instruments designed for studying solar oscillations have been developed at the Sayan observatory. A double solar telescope using two Jensch-coelostats and two objective lenses provides the capability to filter lower-order modes. This instrument is also used (in the single-telescope mode) for making observations of the mean magnetic field of the Sun. Spatially-differential methods based on polarization separation of images are best suited for investigations of local oscillations and higher-order modes. These methods make it possible to carry out narrow-band spatial filtering of large wave numbers. They are useful when investigating contrast oscillations as well as the oscillations and rotation of sunspots and other solar features.     

The evolution of spokes in Saturn's B ring

The optical appearance of spokes was studied in high resolution (?200 km/lp) images obtained by Voyager 2. Spokes are classified into three categories. (1) Extended spokes are seen in the distance interval of 100,000 to 112,000 km from Saturn's center. They have diffuse edges and are slightly wedge shaped. Their width at the base (towards Saturn) is about 20,000 km. Their active times (during which they increase in width) range from 4000 to 12,000 sec. (2) Narrow spokes are found in the distance range 104,000 to 116,000 km, have sharply defined edges, and are narrowest at the corotation distance (112, 300 km). Their typical radial extension and width is 6000 and 2,000 km, respectively. (3) Filamentary spokes are found outside 110,000 km mostly joined with a wider spoke further in. They are typically 3000 km in length and 500 km in width. Their active time is less than 1000 sec. Several narrow spokes were observed during formation along radial lines in the sunlit portion of the ring. The formation time is typically ?5 min for a 6000-km-long spoke. The rate of spoke formation is highest at the morning ansa outside Saturn's shadow. Several spokes have been found where one edge revolves with Keplerian speed whereas the other edge stays radial. Recurrent spoke patterns have been observed at the period of Saturn's rotation. From edge-on views of the ring system, an upper limit for the height of spokes of 80 km is derived.     

Evidence for beamed electrons in a limb X-ray flare observed by HXIS

X-ray images taken by the Hard X-Ray Imaging Spectrometer (HXIS) aboard SMM during the 1980, November 18 limb flare are analysed. The temporal and spatial evolutions of the X-radiation are described. They differ significantly for hard and soft X-rays. During the elementary flare bursts energetic photons are predominantly emitted from a region close to the solar limb. In contrast, the soft X-ray sources are situated higher in the solar atmosphere. The observed X-ray spectra, in particular those emitted from small source regions at various altitudes, were fitted to power laws. Analysis of the spatial variation of the spectral index shows that there is a systematic tendency of the spectra to get harder with decreasing source altitude, especially during the elementary flare bursts. This fact is in agreement with the existence of nonthermal electron beams precipitating from the corona towards the denser layers of the solar atmosphere.