Showing papers in "Annales Geophysicae in 1985"

Observations in the upper atmosphere of infrasonic waves from natural or artificial sources: a summary

Abstract: Revue des effets de sources acoustiques sur la haute atmosphere Les sources naturelles sont: les tremblements de terre, les eruptions volcaniques, les aurores polaires, les orages; les sources artificielles: lancers de fusee, les explosions On etudie la formation de la perturbation (onde itinerante puis action collisionnelle sur l'ionosphere) et sa propagation

Statistical properties of fast magnetoacoustic shock waves in the solar wind between 0.3 Au and 1 Au: Helios-1,2 observations

Abstract: Resultats d'une etude statistique sur 178 ondes MHD rapides enregistrees a bord d'Helios 1 et 2, entre janvier 1975 et decembre 1980

The maser synchrotron instability in an inhomogeneous medium: application to the generation of the auroral kilometric radiation.

Abstract: On applique une instabilite synchrotron maser (ISM) a un plasma froid dans une theorie de la prevision de l'excitation des ondes de mode X juste au-dessus de la coupure. On verifie que cette theorie est applicable au plasma auroral homogene

Observations of noctilucent clouds from north-west Europe

Abstract: Analyse de 19 annees d'observations Discussion des effets du cycle solaire, des variations saisonnieres, diurnes, lunaires et geomagnetiques Influence de la dynamique atmospherique

Auroral E-region diagnosis by means of nonlinearly stabilized plasma waves

Abstract: Les publications recentes (Nielsen et Schlegel, 1983) ont indique que les vitesses de phase des ondes BF dans la region E sont plus faibles que la vitesse de derive des electrons telle que les ondes de derive sont instables. Ceci est en accord avec des mesures in situ (Bahnsen, 1978). On reetudie ces donnees en modifiant la theorie d'instabilite lineaire de Sudan (1983) pour les rendre conformes a un taux de croissance zero au-dessus du seuil. Ceci amene a des ondes a la vitesse acoustique ionique avec une amplitude stabilisee a un niveau conforme aux observations

Evaluation of the drag coefficient considering the effects of mobility of the roughness elements

Abstract: Installation d'une plate-forme fixe a 100 m du rivage, au-dessus d'une profondeur de 3 m d'eau, dans le lac Leman. Les donnees de v, t et hauteur des vagues (profils sur 10 min) ont ete analysees pour obtenir le coefficient de trainee correspondant a une vitesse du vent comprise entre 7 et 17 m/s, en presence d'une faible stratification thermique. Apres le rappel de la formule donnant le coefficient neutre, ajuste pour la stratification thermique, et la description du programme experimental, on presente la rugosite de la surface de l'eau incluant deux equations. Celles-ci expliquent la longueur de rugosite en termes des caracteristiques principales de l'etat de la mer. Examen du calcul de la rugosite a l'aide d'une procedure du type Donelan (separation du spectre en composantes ondes longues et ondes courtes). On constate que la contribution des ondes courtes est plus de 2 fois celles des ondes longues

Ion compositions in the auroral ionosphere as observed by EISCAT

Abstract: Analyse des mesures d'abondance de O + et de ses variations saisonnieres. On observe que la region F est en equilibre photochimique avec des variations de la composition ionique (NO + /O + ) en periode de perturbation

General theory of the alkali metals present in the earth's upper atmosphere. I - Flux model: Chemical and dynamical processes

Abstract: On presente un modele general simulant les variations des metaux alcalins (sodium potassium, lithium) mesures par lidar et observations photometriques avec leurs variations spatiaux-temporelles On determine les flux des composants metalliques, le role des sources meteoriques et les reactions d'aglomeration de creation d'ions hydrates

The quadrupole ionosphere.

Abstract: Schema d'une paleo-ionosphere ayant pu exister quand le champ geomagnetique etait quadripolaire durant des periodes d'inversion geomagnetique

Electrostatic wave propagation and trapping near the magnetic equator

Abstract: Results of a two-dimensional ray tracing computer code, based on Snell's law, for electrostatic wave propagation in a dipole magnetic field are discussed. A survey of possible ray paths varying a wide range of parameters is conducted for low-harmonic Bernstein modes in a high-density plasma. It is shown that the ray paths exhibit similarity with radial distance and that there exists the possibility of two classes of wave statistics of the equator: a broad emission region extending to about + or - 4 deg and a class of events restricted to the smaller region of 1-2 deg about the magnetic equator. The regulating parameter between these two types of events is the transition energy from the isotropic background electrons to the unstable distribution of superthermals. Ray paths for propagation in the magnetic equatorial plane are considered and an explanation is given for ray focusing in the equatorial plane based on electron gyroradius considerations.

Whistler-triggered VLF noise bursts observed on the DE-1 satellite and simultaneously at Antarctic ground stations

Abstract: Simultaneous observations of whistler-triggered very low-frequency noise bursts on the ground at Anarctic stations, Halley and Siple, and on the high-altitude satellite DE-1 are reported. Results of a case study from June 25, 1982 in which the satellite data were recorded near 25 deg south magnetic latitude and the L = 4.7 magnetic shell, are presented. Analysis indicates that the chorus bursts that are triggered in whistler ducts travel downwards in the ducts to low altitudes in the ionosphere, and that propagation to DE-1 is by upward reflection into a nonducted mode. A means of estimating the propagation characteristics of the wave bursts is provided by comparisons of nonducted signals from the Siple transmitter and discrete periodic emissions. The ducted-nonducted mode conversion process is a mechanism for the large-scale spreading into the magnetosphere of coherent whistler-mode wave energy which is generated, amplified, or triggered in small localized ducts. The DE-1 data show that a strong interaction exists between whistler-triggered noise bursts and prevailing hiss levels.