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891.
A simple matching technique is developed which allows us to compute the response of the solar envelope to perturbations which occur within the solar convective region, and in timescales of importance to climate. This technique is applied to perturbation of the convective efficiency (-mechanism), and of the non-gas component of the pressure in different regions of the convection zone (-mechanism). The results indicate that while either perturbation affects the solar luminosity, the -mechanism has almost no effect on the solar outer radius, regardless of the affected region, whereas the -mechanism produces radius changes which may be large if the location of perturbation is deep enough.  相似文献   
892.
We determine empirical damping constants for 73 selected Fe i lines following the method of Gurtovenko and Kondrashova (1980), employing high-quality observations and the accurate list of Fe i oscillator strengths by Gurtovenko and Kostik (1980).The results show: (i) No increase of the enhancement factor to van der Waals broadening with excitation potential, as predicted by Edmunds (1975), and with the frequency of the transition (Figure 1); (ii) a substantial part of the commonly-used enhancement factor for weaker lines is not due to collisional damping (Figure 2), but to a misrepresentation of the inhomogeneous structure of the deep photosphere. This false damping effect is not seen in the stronger lines which yield an average damping constant : 1.36 1.5 6.  相似文献   
893.
The evolution of vector photospheric magnetic fields has been studied in concert with photospheric spot motions for a flare-productive active region. Over a three-day period (5–7 April, 1980), sheared photospheric velocity fields inferred from spot motions are compared both with changes in the orientation of transverse magnetic fields and with the flare history of the region. Rapid spot motions and high inferred velocity shear coincide with increased field alignment along the B L= 0 line and with increased flare activity; a later decrease in velocity shear precedes a more relaxed magnetic configuration and decrease in flare activity. Crude energy estimates show that magnetic reconfiguration produced by the relative velocities of the spots could cause storage of 1032 erg day–1, while the flares occurring during this time expended 1031 erg day–1.Maps of vertical current density suggest that parallel (as contrasted with antiparallel) currents flow along the stressed magnetic loops. For the active region, a constant-, force-free magnetic field (J = B) at the photosphere is ruled out by the observations.Presently located at NASA/MSFC, Huntsville, Ala. 35812, U.S.A.  相似文献   
894.
The main results of a study of a catalogue of physical parameters of 1041 spectroscopic binaries are presented. The distribution of spectroscopic binaries over all main parametersM 1, a, e, M1/M2, P, and certain dependencies between some of them have been found.
  1. It appears that among bright (m v?3 m –5 m ) stars withM?1M , about 40% are apparently spectroscopic binaries with comparable masses of components.
  2. The majority of spectroscopic binaries with the ratio of the large semiaxis of the orbit to the radius of the primarya/R 1?20, have eccentricities close to zero. This is probably a consequence of the tidal circularization of orbits of close binaries by viscous friction.
  3. The discovery of duplicity of double-line spectroscopic binaries is possible only if the semiamplitude of radial velocityK 1 is almost 10 times higher than the semiamplitude of the radial velocity of a single-line spectroscopic binary of the same mass.
  4. Double-line spectroscopic binaries witha/R ?6(M 1/M )1/3,M 1M 2?1.5M are almost almost absent, and the number of stars witha/R ?6(M 1/M )1/3,M 1≈1.5M is relatively low.
  5. The distribution of unevolved SB stars over the large semiaxis may be described by the expression d(N d/Nt)≈0.2 d loga for 6(M 1/M )1/3?a/R ?100.
  6. The intial mass-function for primaries of spectroscopic binaries is the same Salpeter function dN d≈M 1 ?2.35 dM 1 for 1?M 1/M ?30.
  7. It is possible to explain the observed ratio of the number of single-line spectroscopic binaries to the number of double-line binaries if one assumes that the average initial mass ratio is close to 1 and that the mass of the postmass-exchange remnant of the primary exceeds the theoretical one and/or that half of the angular momentum of the system is lost during mass-exchange.
  8. The above-mentioned distributions ofM 1 anda and assumptions on the mass of remnant and/or momentum loss also allow us to explain the observed shapes of dN/dM, dN/dq, and dN/da distributions after some selection effects are taken into account.
  相似文献   
895.
The equatorial photospheric rotation rate has been observed on 14 days in 1978–1980. The resulting rotation rate, = 14.14±0.04°/day, is 2% slower than the rate as observed for long-lived sunspots.Stationed at Kitt Peak National Observatory.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.  相似文献   
896.
Photoelectric observations of the light intensity from the solar crescent before and after totality were made during the eclipses of 7 March, 1970 and 26 February, 1979. Effective wavelengths were determined by interference filters of 20 nm bandwidth. To obtain the limb darkening function, the resulting intensity curves were analyzed by an extension of the method of Julius in which we take into account the actual lunar limb profile. The limb darkening function at 433 nm was obtained for the region 0.937 < sin < 0.9999. Our results are in good agreement with existing center-to-limb measurements in the region of overlap which extends to sin = 0.99. Additional data were obtained at 600 nm for 0.994 < sin < 0.9999. The curves at both wavelengths show a distinctive limb brightening effect at sin = 0.999.  相似文献   
897.
We consider a system of planets defined by a given distribution of mean mean motions and masses: we represent the osculating elliptic elements of their heliocentric orbits by quasi-periodic functions of time, through a method adapted to the commensurability case; these functions are the sum of the general solution of a critical system, expressed in long-period terms, and of a particular solution. As in the B. Brown's method (applied to the galilean satellites), the critical system contains the secular terms, the longperiod terms (great inequalities), and the resonant terms; the particular solution consists of short-period terms only, whose amplitude is an explicit function of the solution of the critical system.If all the long-period terms in the critical system are harmonic of one fundamental term, we can perform a simple change of variables which transforms the critical system in an autonomous one, and thus we reduce the resolution to an eigenvalue problem. Applying that to the galilean satellites of Jupiter and neglecting the solar perturbations, we obtain a differential system with constant coefficients, whose linear part concerns all the variables (including the major-axes and the mean longitudes) and gives, as a first approximation, the great inequalities, the free oscillations and the libration; nevertheless this solution agrees already with known results, but should be improved by taking into account the non-linear parts and the solar terms in a new approximation.

Proceedings of the Conference on Analytical Methods and Ephemerides: Theory and Observations of the Moon and Planets. Facultés universitaires Notre Dame de la Paix, Namur, Belgium, 28–31 July, 1980  相似文献   
898.
Summary Most finite-difference numerical weather prediction models employ vertical discretizations that are staggered, and are low-order (usually second-order) approximations for the important terms such as the derivation of the geopotential from the hydrostatic equation, and the calculation of the vertically integrated divergence. In a sigma-coordinate model the latter is used for computing both the surface pressure change and the vertical velocity. All of the above-mentioned variables can diminish the accuracy of the forecast if they are not calculated accurately, and can have an impact on related quantities such as precipitation.In this study various discretization schemes in the vertical are compared both in theory and in practice. Four different vertical grids are tested: one unstaggered and three staggered (including the widely-used Lorenz grid). The comparison is carried out by assessing the accuracy of the grids using vertical numerics that range from second-order up to sixth-order.The theoretical part of the study examines how faithfully each vertical grid reproduces the vertical modes of the governing equations linearized with a basic state atmosphere. The performance of the grids is evaluated for 2nd, 4th and 6th-order numerical schemes based on Lagrange polynomials, and for a 6th-ordercompact scheme.Our interpretation of the results of the theoretical study is as follows. The most important result is that the order of accuracy employed in the numerics seems to be more significant than the choice of vertical grid. There are differences between the grids at second-order, but these differences effectively vanish as the order of accuracy increases. The sixth-order schemes all produce very accurate results with the grids performing equally well, and with the compact scheme significantly outperforming the Lagrange scheme. A second major result is that for the number of levels typically used in current operational forecast models, second-order schemes (which are used almost universally) all appear to be relatively poor, for other than the lowest modes.The theoretical claims were confirmed in practice using a large number (100) of forecasts with the Australian Bureau of Meteorology Research Centre's operational model. By comparing test model forecasts using the four grids and the different orders of numerics with very high resolution control model forecasts, the results of the theoretical study seem to be corroborated.With 8 Figures  相似文献   
899.
We performed an experimental study using scale models in a hydrodynamic rotating channel, concerning the interactions between fluid flows and obstacles of different shapes. The study was meant to analyze the characteristics of the wakes observed on the lee side of quasi-bidimensional obstacles, in a neutral atmosphere.The obstacles were half-cylinders (with aspect ratio 0.87), placed transversally on the channel bottom and totally submerged in the fluid. We call them quasi-bidimensional since their width was a little smaller than the channel width, thus allowing the flow to partially go round their edges.The simulations were performed in the rotating hydraulic channel of ICG-CNR in Turin, and included various conditions of rotation period and flow speed. An interesting behaviour of the wakes was found on the lee side of subsynoptic-scale obstacles, modelled in conditions of Reynolds-Rossby similitude. More precisely, if a given threshold of flow velocity is exceeded, wake size is constant and is fully determined by the height of the obstacle.  相似文献   
900.
Summary Hydrostatic and nonhydrostatic simulation models are employed to study the intensification of a terrain drag-induced dryline. The study develops a multi-stage theory for the evolution of the dryline including the concentration of potential vorticity accompanying meso-gamma scale dryline bulges.The numerical simulations indicate three fundamental stages of dryline intensification all of which are either directly or indirectly a result of the terrain-drag on the mid/upper-tropospheric jet stream by the Front Range of the Colorado Rocky Mountains. The first stage involves the downward momentum flux accompanying a large amplitude hydrostatic mountain wave which induces a downslope windstorm along the lee slopes. The surge of momentum (i.e., the dry, warm air associated with the downslope windstorm) propagates down the leeslope and modifies an existing weak dryline boundary. As the downslope windstorm initiates an undular bore along the lee slopes, the high momentum gradient which propagates downstream accompanying the bore, as well as the strong lower tropospheric sinking motions ahead of the bore, contract the scale of the surface moisture boundary between the dry air from above the leeslope and the moist air over the High Plains. This process further strengthens the dryline.The second stage involves the coupling of the terrain drag-induced along-stream ageostrophic front within the midtroposphere to the boundary layer through a thermally-indirect circulation. As the along-stream ageostrophic circulation intensifies within the middle troposphere down-stream from the mountain wave, sinking air parcels originating above 40 kPa descend to below 60 kPa over the High Plains where surface pressures are, only 85 kPa. These descending air parcels within the upstream branch of the along-stream ageostrophic thermally-indirect circulation contain high values of momentum and very low dewpoint values. As the planetary boundary layer (PBL) deepens due to surface warming during the morning hours, momentum and dry air from the midtropospheric along-stream ageostrophic front are entrained into the PBL. This process amplifies the bore-induced hydrostatic dryline bulge via low-level ageostrophic confluence.Finally, regions of low Richardson number (arising from strong vertical shears) within the amplifying midtropospheric along-stream ageostrophic thermally-indirect circulation become preferred regions for the development of non-hydrostatic evanescent internal gravity waves. These waves are embedded within the hydrostatic along-stream front above the low-level dryline and are accomapanied by very significant values of vertical momentum flux which act to focus the meso-gamma scale structure of the dryline into smaller scale bulges where low-level winds and vorticities are very high. This meso-gamma scale process follows the hydrostatic tilting and vortex tube stretching which creates meso-beta scale maxima of mid-lower tropospheric vorticity. The turbulent momentum fluxes accompanying wavebreaking within the nonhydrostatic dryline bulge create very large (i.e., stratospheric values of) potential vorticity near 70 kPa due to the nonconservation of potential vorticity on isentropic surfaces.With 30 Figures  相似文献   
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