Three quiescent prominences were observed in the Ca ii K-line and a fourth one also in the H-line at Oslo Solar Observatory, Harestua, and reduced by Rustad (1974) and by Engvold et al. (1980). These data are used to study the distribution of the line-of-sight velocity component, N(u0). It is pointed out that in a stationary and isotropic case, N(u0) should be a gaussian distribution. For each of the sets of measurements gaussians were therefore fitted by a least square procedure. The range in observed velocities varies considerably between the prominences. For the best observed prominence more than 70% of the kinetic energy is in the supersonic range. In the other cases none or only an insignificant part of the observations exceed the velocity of sound. Considerable deviations from gaussian distributions are apparent for the smallest velocities. This distortion shows up conspicuously in the slope of the energy spectrum, a parameter that may be used as a rough measure of spectral resolution.If it is assumed that we have to do with MHD-turbulence as described by Kraichnan (1965), a characteristic relationship should exist between velocity and eddy size. When supersonic velocities are present, compressibility effects may severely alter this relationship. The possibility of observational confirmation is discussed.If a turbulent velocity field is indeed present, the heat conductivity and other transport coefficients may be significantly altered as compared to the atomic values. 相似文献
The influence of an internal boundary layer and a roughness sublayer on flux–profile relationships for momentum and sensible heat have been investigated for a closed beech forest canopy with limited fetch conditions. The influence was quantified by derivation of local scaling functions for sensible heat flux and momentum (h and m) and analysed as a function of atmospheric stability and fetch. For heat, the influences of the roughness sublayer and the internal boundary layer were in agreement with previous studies. For momentum, the strong vertical gradient of the flow just above the canopy top for some wind sectors led to an increase in m, a feature that has not previously been observed. For a fetch of 500 m over the beech forest during neutral atmospheric conditions, there is no height range at the site where profiles can be expected to be logarithmic with respect to the local surface. The different influence of the roughness sublayer on h and m is reflected in the aerodynamic resistance for the site. The aerodynamic resistance for sensible heat is considerably smaller than the corresponding value for momentum. 相似文献
Three different oscillatory models of adiabatic stars are reinvestigated. These are the homogenous model, the inverse square model and the Roche model. The ratio between the amplitude of the oscillations and the distance from the center is developed in a power series. For physical conclusions to be drawn, it turns out to be crucial if the power series is divergent or convergent. Mathematical arguments are given which show that the power series are really divergent for all three models. 相似文献
Cores from boreholes penetrating late Quaternary, glacial, interglacial and postglacial sediments and the underlying late Cenozoic delta complex of the southern North Sea have been examined for their magnetic properties. A magnetic polarity stratigraphy has been established as an aid to biostratigraphic dating of the sediments; the Kaena-Gauss and Gauss—Matuyama transitions and the base and top of the Olduvai subchron have been identified. The strength and stability of laboratory-induced isothermal remanent magnetisation display clear magneto-petrological variations, which match lithostratigraphic changes in the cores. Principal component analysis has picked out a basin-wide and palaeoenvironmental consistency in the magnetic data. Large, multi-domain magnetite grains predominate in the post-deltaic and fluvio-deltaic sediments, whereas smaller greigite or titanomagnetite grains are concentrated in the intertidal and marine deltaic facies. Since heavy mineral analysis indicates that most of the deltaic detritus derived from common source areas, the differences in magnetic mineralogy have probably been caused by the sediment transport processes operating within the delta complex. 相似文献
We investigate how well the variability of extreme daily precipitation events across the United Kingdom is represented in a set of regional climate models and the E-OBS gridded data set. Instead of simply evaluating the climatologies of extreme precipitation measures, we develop an approach to validate the representation of physical mechanisms controlling extreme precipitation variability. In part I of this study we applied a statistical model to investigate the influence of the synoptic scale atmospheric circulation on extreme precipitation using observational rain gauge data. More specifically, airflow strength, direction and vorticity are used as predictors for the parameters of the generalised extreme value (GEV) distribution of local precipitation extremes. Here we employ this statistical model for our validation study. In a first step, the statistical model is calibrated against a gridded precipitation data set provided by the UK Met Office. In a second step, the same statistical model is calibrated against 14 ERA40 driven 25?km resolution RCMs from the ENSEMBLES project and the E-OBS gridded data set. Validation indices describing relevant physical mechanisms are derived from the statistical models for observations and RCMs and are compared using pattern standard deviation, pattern correlation and centered pattern root mean squared error as validation measures. The results for the different RCMs and E-OBS are visualised using Taylor diagrams. We show that the RCMs adequately simulate moderately extreme precipitation and the influence of airflow strength and vorticity on precipitation extremes, but show deficits in representing the influence of airflow direction. Also very rare extremes are misrepresented, but this result is afflicted with a high uncertainty. E-OBS shows considerable biases, in particular in regions of sparse data. The proposed approach might be used to validate other physical relationships in regional as well as global climate models. 相似文献
Stable weather conditions together with extensive use of coal combustion often lead to severe smog episodes in certain urban environments, especially in Eastern Europe. In order to identify the specific sources that cause the smog episodes in such environments, and to better understand the mixing state and atmospheric processing of aerosols, both single particle and bulk chemical characterization analysis of aerosols were performed in Krakow, Poland, during winter 2005.Real-time measurements of the bulk PM10 aerosol during a severe smog episode (PM10 mass > 400 µg m− 3) showed a stable concentration of black carbon in the aerosol, and an increase in the sulphate and chlorine mass contributions towards the end of the episode. Chemical characterization of single particles further helped to identify residential coal burning as the main source that caused this severe smog episode, consisting of single particles with major signals for carbon with simultaneous absence of sulphate, chlorine and calcium. Particles from industrial coal combustion gained importance towards the end of that episode, after residential coal combustion was switched off, indicated by an increase of the percentage of sulphate and chlorine containing particles. Traffic was not a significant source during the severe smog episode. During a lighter smog episode, residential and industrial coal combustion was still predominant, with an increased contribution of traffic and processed/aged aerosols. On a clean day, particle classes containing nitrate were the most abundant. In addition, the aerosol was more internally mixed showing that there were more sources contributing to the total aerosol population. 相似文献
Abstract— Evidence from meteorites shows that the first solids to form in the solar system, calcium‐aluminum‐rich inclusions (CAIs), were transported outward from the Sun by several AU in the early solar system. We introduce a new concept of levitation and outward transport of CAIs at the surface of protoplanetary disks. Thermal radiation from the disk and the Sun can cause particles to levitate above the disk and drift outward through a process known as photophoresis. During normal conditions this process only works for dust‐sized particles but during high luminosity events like FU‐Orionis outbursts, the process can provide an efficient lift and transport of CAIs from within the inner 1 AU to a distance of several AU from the Sun. This might explain why CAIs, believed to have formed close to the Sun, are common in meteorites believed to come from the outer asteroid belt but are rare or absent in samples from the inner solar system. Since the process only works during the FU‐Orionis event and only for particles up to cm‐size, it may also explain why the CAIs we find in meteorites appear to have formed within a short period of time and why they rarely exceed cm size. 相似文献
The Swedish Deep Drilling Program (SDDP) has been initiated to study fundamental problems of the dynamic Earth system, its natural history and evolution. Many key scientific questions can be addressed through in situ investigations only, requiring deep continental drilling. Some are unique to Scandinavia, most are of international interest and significance. At present, five core projects ( Fig. 1 ) with international teams are integrating scientific problems with societal and industrial applications. If SDDP succeeds to attract the funding required, Sweden will have a number of world‐class boreholes at key locations by 2020. Figure 1 Open in figure viewer PowerPoint Locations of SDDP drilling project proposals. PFDP—Postglacial Fault Drilling Project; PaMVAS—Palaeoproterozoic mineralized volcanic arc systems: the Skellefte District; COSC—Collisional Orogeny in the Scandinavian Caledonides; DRL—The Dellen Impact Crater, a geoscientific deep rock laboratory; SELHO—Svecofennian accretion, an example of the early structural evolution in a large hot orogen; CISP—Concentric Impact Structures in the Palaeozoic: the Lockne and Siljan craters. Background and inset image from Blue Marble Next Generation data set (NASA Earth Observatory, http://earthobservatory.nasa.gov/Features/BlueMarble/ ). 相似文献
The newly discovered Ritland impact structure (2.7?km in diameter) has been modeled by numerical simulation, based on detailed field information input. The numerical model applies the SOVA multi-material hydrocode, which uses the ANEOS equation of state for granite, describing thermodynamical properties of target and projectile material. The model displays crater formation and possible ejecta distribution that strongly supports a 100?m or less water depth at the time of impact. According to the simulations resurge processes and basinal syn- and postimpact sedimentation are highly dependent on water depth; in more than 100?m of water depth, much more powerful resurge processes are generated than at water depths shallower than 100?m (the Ritland case). In Ritland the 100?m high (modeled) crater rim formed a barrier and severely reduced the resurge processes. In the case of deeper water, powerful resurge processes, tsunami wave generations and related currents could have triggered even more violent crater fill sedimentation. The presented model demonstrates the importance of understanding the interactions between water layer and both syn-impact crater fill and ejecta distribution. According to the presented simulations ejecta blocks up to 10?m in diameter could be transported up to about 5?km outside the crater rim. 相似文献
