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Determination of low energy photoelectron distribution from plasma line measurements at Saint Santin
The plasma lines observed by the French incoherent scatter radar during the period 1973–1974 are studied. Two methods are used to determine the steady-state photoelectron flux from plasma line measurements; one using a Maxwellian model for the photoelectron distribution and the other by solving (numerically) the differential equation that is satisfied by the distribution.The direct numerical calculation of the photoelectron flux is used to obtain theoretical kTp values which are compared with those from the plasma line observation. The comparison leads to the conclusion that there must be a sharp increase of the photoelectron flux when the energy decreases below 4 ～ 5 eV.This result, in agreement with rocket and satellite measurements of the low energy photoelectron flux, is used to bear a new insight to the problem of the electron-gas heat balance: the problem is reduced to the need of an additional photoelectron flux production below 5 eV. 相似文献
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Lava solidification is controlled by two mechanisms: external cooling and gas exsolution, the latter inducing crystallization due to increasing liquidus temperature. The andesite lava dome of the Soufriere Hills Volcano, Montserrat, is an extrusion dominated by crystallization caused by gas exsolution where cooling is unimportant in controlling emplacement. In the magma chamber the magma has an estimated viscosity of 7 × 106 Pa s. During ascent, gas exsolution caused the magma to extrude in a highly crystalline state, with only 5–15% residual melt, viscosities in the range 1013 –1014 Pa s and mechanical strength > 1 MPa. Deformation can be heterogeneous with extrusion along shear zones. Rheological stiffening in the upper conduit also causes large overpressures, shallow seismicity, and cyclic patterns of dome extrusion. Gas-rich porphyritic andesites tend to be the least mobile kind of lava, because transition from magma into hot crystalline material was reached during ascent. 相似文献
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E. Lastennet T. Lejeune E. Oblak P. Westera R. Buser 《Astrophysics and Space Science》2002,280(1-2):83-87
The Basel Stellar Library (BaSeL) is a library of synthetic spectra which has already been used in various astrophysical applications
(stellar cluster studies, characterization and choice of the COROT potential targets, eclipsing binaries,...). This library
could provide useful indications to 1) choose the best photometric system for the GAIA strategy by evaluating their expected
performances and 2) apply systematically the BaSeL models for any sample of the GAIA targets. In this context, we describe
one of the future developments of the BaSeL interactive web site to probe the GAIA photometric data: an automatic determination
of atmospheric parameters from observed colours.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Solutions of gum rosin and acetone reproduce the volatile- and temperature-dependent viscosity, together with the phase behaviour, of hydrated magmas. A range of experimental exsolution conditions was investigated, including the variation of supersaturation, rate of decompression, solution temperature and volatile content. Degassing processese were controlled by the formation of an exsolution interface above a supersaturated liquid. The end-products ranged from a mildly degassed liquid to a solid foam, which preserved strained vesicles. Solutions of gum rosin and acetone are proposed as a suitable analogue system with which to study magma degassing processes. 相似文献
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Field-aligned electric currents flow in the magnetosphere in many situations of fundamental geophysical interest. It is shown here that the incoherent backscatter technique can be used to measure these currents when the plasma line can be observed. To our knowledge this has not been proposed before. The technique provides a ground-based means of measuring these currents which complements the rocket and satellite ones. 相似文献
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Local variability in total electron content can seriously affect the accuracy of GNSS real-time applications. We have developed
software to compute the positioning error due to the ionosphere for all baselines of the Belgian GPS network, called the Active
Geodetic Network (AGN). In a first step, a reference day has been chosen to validate the methodology by comparing results
with the nominal accuracy of relative positioning at centimeter level. Then, the effects of two types of ionospheric disturbances
on the positioning error have been analyzed: (1) Traveling ionospheric disturbances (TIDs) and (2) noise-like variability
due to geomagnetic storms. The influence of baseline length on positioning error has been analyzed for these three cases.
The analysis shows that geomagnetic storms induce the largest positioning error (more than 2 m for a 20 km baseline) and that
the positioning error depends on the baseline orientation. Baselines oriented parallel to the propagation direction of the
ionospheric disturbances are more affected than others. The positioning error due to ionospheric small-scale structures can
be so identified by our method, which is not always the case with the modern ionosphere mitigation techniques. In the future,
this ionospheric impact formulation could be considered in the development of an integrity monitoring service for GNSS relative
positioning users. 相似文献
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Model complexity and data requirements in snow hydrology: seeking a balance in practical applications 
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下载免费PDF全文 Francesco Avanzi Carlo De Michele Samuel Morin Carlo Maria Carmagnola Antonio Ghezzi Yves Lejeune 《水文研究》2016,30(13):2106-2118
We investigate the problem of balancing model complexity and input data requirements in snow hydrology. For this purpose, we analyze the performance of two models of different complexity in estimating variables of interest in snow hydrology applications. These are snow depth, bulk snow density, snow water equivalent and snowmelt run‐off. We quantify the differences between data and model prediction using 18 years of measurements from an experimental site in the French Alps (Col de Porte, 1325 m AMSL). The models involved in this comparison are a one‐layer temperature‐index model (HyS) and a multilayer model (Crocus). Results show that the expected loss in performance in the one‐layer temperature‐index model with respect to the multilayer model is low when considering snow depth, snow water equivalent and bulk snow density. As for run‐off, the comparison returns less clear indications for identification of a balance. In particular, differences between the models' prediction and data with an hourly resolution are higher when considering the Crocus model than the HyS model. However, Crocus is better at reproducing sub‐daily cycles in this variable. In terms of daily run‐off, the multilayer physically based model seems to be a better choice, while results in terms of cumulative run‐off are comparable. The better reproduction of daily and sub‐daily variability of run‐off suggests that use of the multilayer model may be preferable for this purpose. Variation in performance is discussed as a function of both the calibration solution chosen and the time of year. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Emission profiles of the 6300Åline are determined from OGO 4 data in the dark ionosphere during conjugate sunrise. From Saint-Santin electron density profile measurements, it is shown that, for the two cases studied in December 1967, the recombination cannot account for the measured O1D emission profiles. However, direct photoelectron-oxygen excitation can reproduce the data: if the photoelectron escape flux in the sunlit ionosphere, computed from standard photoelectron production, is transmitted through the field tube with an additional attenuation of 0.6 due to angular diffusion through photoelectron-electron and photoelectron-ion Coulomb collisions, the Hinteregger (1965) solar flux data must be increased by a factor 2, which agrees with previous results. 相似文献