La forme rotationnelle des équations de la dynamique atmosphérique et les invariants du mouvement de l'air     

J. Van Mieghem 《Meteorology and Atmospheric Physics》1954,7(1):16-28

Résumé Après avoir rappelé quelques notions de calcul tensoriel et les équations de la dynamique atmosphérique en coordonnées généralisées, l'auteur établit l'équation fondamentale de la rotationnelle absolue de l'air. Diverses formes de cette équation sont mentionnées. La première de ces formes est celle d'un bilan qui permet de définir le transport et le taux de production de la rotationnelle absolue de l'air. De la forme particulière de ce transport, il résulte que ce bilan se réduit à un bilan dans un espace à deux dimensions. Deux exemples illustrent les formules générales, le premier, en coordonnées sphériques (, ,r), le second, en coordonnées (, , ) où est un scalaire quelconque (pression atmosphérique, température potentielle, ...). Une autre forme de l'équation fondamentale est celle qui donne le taux d'accroissement individuel d'une composante de la rotationnelle absolue. Cette forme conduit à l'équation d'Ertel. En terminant, l'auteur généralise l'invariant d'Ertel-Rossby.

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Summary Having recalled some results of the tensor analysis and the equations of atmospheric motion in general coordinates, the writer establishes the fundamental equation of the absolute vorticity. Different forms of this equation are mentioned. One of these is the equation of balance from which it is possible to deduce the definition of transport and production of vorticity. It is shown that the equation of balance of the absolute vorticity may be reduced to an equation of balance in two-dimensional space. Two examples illustrate the general equations and formulas: the first example, in spherical coordinates (, ,r), the second one in the coordinates (, , ) where is an arbitrary single-valued scalar quantity (pressure, potentiel temperature, ...). Another form of the absolute vorticity equation expresses the individual change of an arbitrary component of the absolute vorticity. This form leads toErtel's equation. Finally, the writer generalizes theErtel-Rossby invariant.

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Zusammenfassung Nach einer Rekapitulation einiger Resultate der Tensorrechnung und der atmosphärischen Bewegungsgleichungen in generalisierten Koordinaten wird die absolute Wirbelgleichung aufgestellt und es werden verschiedene Formen dieser Gleichung erwähnt. Eine derselben ist die Bilanzformel, aus der die Definition des Wirbeltransports und der Anteil der Wirbelbildung abgeleitet werden können. Es wird gezeigt, daß die Bilanzgleichung des absoluten Wirbels auf eine Bilanzgleichung im zweidimensionalen Raum reduziert werden kann. Die allgemeinen Formeln werden durch zwei Beispiele erläutert: das erste in Kugelkoordinaten (, ,r), das zweite in den Koordinaten (, , ), wo eine beliebige skalare Größe (luftdruck, potentielle Temperatur usw.) darstellt. Eine andere Form der absoluten Wirbelgleichung gibt die individuelle Zunahme einer beliebigen Komponente der absoluten Wirbelstärke wieder; diese Form führt zurErtelschen Gleichung. Zum Schlusse wird dieErtel-Rossbysche Invariante verallgemeinert.

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Buchbesprechungen     

F. Steinhauser  W. Mörikofer  H. Israël  M. Toperczer 《Meteorology and Atmospheric Physics》1953,6(1):114-128

Ohne Zusammenfassung  相似文献   

Hans Benndorf †     

H. Israël  M. Toperczer 《Meteorology and Atmospheric Physics》1953,6(1):111-113

Ohne Zusammenfassung

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Hans Benndorf

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Multi-wavelength observations of the onset phase of a coronal mass ejection     

Innes  D.E.  Inhester  B.  Srivastava  N.  Brekke  P.  Harrison  R.A.  Matthews  S.A.  Noëns  J.C.  Schmieder  B.  Thompson  B.J. 《Solar physics》1999,186(1-2):337-361

The structure and dynamics of the initial phases of a coronal mass ejection (CME) seen in soft X-ray, extreme ultraviolet and optical emission are described. The event occurred on the SW limb of the Sun in active region AR 8026 on 9 April 1997. Just prior to the CME there was a class C1.5 flare. Images taken with the Extreme Ultraviolet Imaging Telescope (EIT) reveal the emergence of a candle-flame shaped extreme ultraviolet (EUV) cavity at the time of the flare. Yohkoh images, taken about 15 min later, show that this cavity is filled with hot X-ray emitting gas. It is most likely that this is the site of the flare. Almost simultaneous to the flare, an H surge or small filament eruption occurs about 50 arc sec northwards along the limb from the EUV cavity. At both the site of the core of the hot, EUV cavity and the filament ejection are X-ray jets. These jets seem to be connected by hot loops near their bases. Both jets disappear within a few minutes of one another.Clear evidence of the CME first appeared in the Large Angle Spectrometric Coronagraph (LASCO) and EIT images 40 min after the flare and onset of the filament ejection. It seems to come from a region between the two X-ray jets. This leads to the speculation that magnetic field reconnection near one footpoint of a loop system triggers reconnection near its other footpoint. The loop system is destabilized and ultimately gives rise to the CME. This possibility is supported by magnetic field and H images taken when the active region was at disk center which show that the active region had a double bipole structure with dark H filaments between the bipoles.  相似文献   

Approaches to analyse and model changes in impacts: reply to discussions of “How to improve attribution of changes in drought and flood impacts”*     

Heidi Kreibich  Veit Blauhut  Jeroen C. J. H. Aerts  Laurens M. Bouwer  Henny A. J. Van Lanen  Alfonso Mejia 《水文科学杂志》2020,65(3):491-494

ABSTRACT

We thank the authors, Brunella Bonaccorso and Karsten Arnbjerg-Nielsen for their constructive contributions to the discussion about the attribution of changes in drought and flood impacts. We appreciate that they support our opinion, but in particular their additional new ideas on how to better understand changes in impacts. It is great that they challenge us to think a step further on how to foster the collection of long time series of data and how to use these to model and project changes. Here, we elaborate on the possibility to collect time series of data on hazard, exposure, vulnerability and impacts and how these could be used to improve e.g. socio-hydrological models for the development of future risk scenarios.  相似文献   

Flexible Automatic Scheduling for Autonomous Telescopes: The MAJORDOME     

Mathieu Bringer  Michel Boër  Cedric Peignot  Gérard Fontan  Colette Mercé 《Experimental Astronomy》2001,12(1):33-48

We have developped a new method for the scheduling ofastronomical automatic telescopes, in the framework of theautonomous TAROT instrument. The MAJORDOME software canhandle a variety of observations, constrained, periodic,etc., and produces a timeline for the night, which may bemodified at any time to take into account the specificconditions of the night. The MAJORDOME can also handletarget of opportunity observations without delay.  相似文献   

Palaeomagnetism of the Ordovician dolerites of the Crozon Peninsula (France)     

H. Perroud  N. Bonhommet  R. Van der  Voo 《Geophysical Journal International》1983,72(2):307-319

Summary. In order to obtain a Lower Palaeozoic pole for the Armorican Massif and to test the origin of the Ibero-Armorican arc, the Ordovician dolerites of the Crozon peninsula have been palaeomagnetically studied. The samples show a multicomponent magnetization which has been revealed by AF and thermal demagnetization and thoroughly investigated with rock magnetic experiments, polished section examinations and K/Ar dating. Four groups of directions have been recognized, often superimposed on each other in an individual sample. One component (D) has always the lowest blocking temperatures and coercivities and is considered to be of viscous origin, acquired recently in situ or in the laboratory during storage. Two components (A and B) are interpreted to be of secondary origin and to correspond to the observed K/Ar age distribution between 300 and 190 Myr. These ages represent the time interval between two regional thermo-tectonic events, associated with the Hercynian orogeny and the intrusion of dykes related to the early opening of the Central Atlantic Ocean and the Bay of Biscay. A fourth component (C) could be of Ordovician or younger Palaeozoic age; it is not clear whether the age of the magnetization is pre- or post-folding, but a pre-folding age would yield a direction of magnetization similar to Ordovician results from the Iberian peninsula. The latter interpretation suggests a fairly high palaeolatitude, which is in agreement with a glacio-marine postulated for sediments overlying the dolerite sills.  相似文献   

Approximate spectral analysis by least-squares fit   总被引：4，自引：0，他引：4  

Petr Vaníček 《Astrophysics and Space Science》1969,4(4):387-391

An approximate method of spectral analysis called successive spectral analysis based upon the mean-quadratic approximation of an empirical function by generalised trigonometric polynomial with both unknown frequencies and coefficients is developed. A few quotations describing some properties of the method as well as one of the possible methods for numerical solution are given.  相似文献   

A dynamical investigation of the conjecture that Mercury is an escaped satellite of Venus     

Thomas C. Van Flandern  Robert S. Harrington 《Icarus》1976,28(4):435-440

The possibility that Mercury might once have been satellite of a Venus, suggested by a number of anomalies, is investigated by a series of numerical computer experiments. Tidal interaction between Mercury and Venus would result in the escape of Mercury into a solar orbit. Only two escape orbits are possible, one exterior and one interior to the Venus orbit. For the interior orbit, subsequent encounters are sufficiently distant to avoid recapture or large perturbations. The perihelion distance of Mercury tends to decrease, while the orientation of perihelion librates for the first few thousand revolutions. If dynamical evolution or nonconservative forces were large enough in the early solar system, the present semimajor axes could have resulted. The theoretical minimum quadrupole moment of the inclined rotating Sun would rotate the orbital planes out of coplanarity. Secular perturbations by the other planets would evolve the eccentricity and inclination of Mercury's orbit through a range of possible configurations, including the present orbit. Thus the conjecture that Mercury is an escaped satellite of Venus remains viable, and is rendered more attractive by our failure to disprove it dynamically.  相似文献   

The transition from elliptic to hyperbolic orbits in the two-body problem by slow loss of mass     

L. Van Der Laan  F. Verhulst 《Celestial Mechanics and Dynamical Astronomy》1972,6(3):343-351

Transition from elliptic to hyperbolic orbits in the two-body problem with slowly decreasing mass is investigated by means of asymptotic approximations.Analytical results by Verhulst and Eckhaus are extended to construct approximate solutions for the true anomaly and the eccentricity of the osculating orbit if the initial conditions are nearly-parabolic. It becomes clear that the eccentricity will monotonously increase with time for all mass functions satisfying a Jeans-Eddington relation and even for a larger set of functions. To illustrate these results quantitatively we calculate the eccentricity as a function of time for Jeans-Eddington functionsn=0(1) 5 and 18 nearly-parabolic initial conditions to find that 93 out of 108 elliptic orbits become hyperbolic.  相似文献