The auroral break-up as related to the interplanetary parameters and the geomagnetic activity

In the present study, we used as a significant indicator of the auroral break-up the "sudden equatorward shift" in arcs or displays. For the dark months of May and June of 1971, auroral observations at Base General Belgrano (78,0° S; 38,8° W) were used. Four-hourly sequences centered at the break-up (t=0) were studied for the following quantities: a) The magnitude of the interplanetary magnetic field (B), b) The southward component of the interplanetary magnetic field (Bz), c) The solar wind speed (V), d) The solar wind electric field (the westward component: E ), e) The auroral electrojet magnetic activity indices (AE, AL, AU). On the basis of the seven substorms studied, one may deduce that an appreciable increase of geomagnetic activity occured about 40 minutes after the energy arrival at the magnetosphere, but it is not enough strong to take place the break-up, it will happen after another period of 35 minutes. This result confirms that a substorm only occurs after a build-up process. The present paper also confirms the possibility of using the auroral zone geomagnetic activity for estimating the solar wind velocity.En el presente trabajo usamos como indicador de la ruptura de aurora al "sudden equatorward shift" en arcos o displays. Para los meses oscuros de mayo y junio de 1971, se usaron observaciones aurorales en la Base General Belgrano (78,0° S; 38,8° W) Se estudiaron las secuencias de cuatro horas centradas en la ruptura (t=0) para las siguientes variables: a). La amplitud del campo magnético interplanetario (B), b) La componente sur del campo magnético interplanetario (Bz), c) La velocidad del viento solar (V), d) El campo eléctrico del viento solar (la componente oeste: E), c) Los índices de actividad magnética del electrochorro auroral (AE, AL, AU) Sobre la base de las siete subtormentas estudiadas uno puede deducir que ocurrió un incremento apreciable de la actividad geomagnética aproximadamente 40 minutos después de la llegada de la energía a la magnetósfera, pero no han sido lo suficientemente fuertes para tener lugar durante la ruptura, eso sucederá después de otro período de 35 minutos. Este resultado confirma que una sub-tormenta solo ocurre después de un proceso tipo "build-up". El presente trabajo también confirma la posibilidad de usar la actividad geomagnética de la zona auroral para estimar la velocidad del viento solar.Material digitalizado en SEDICI gracias a la colaboración de la Facultad de Ciencias Astronómicas y Geofísicas (UNLP).Asociación Argentina de Geofísicos y Geodesta

The auroral break-up as related to the interplanetary parameters and the geomagnetic activity

In the present study, we used as a significant indicator of the auroral break-up the "sudden equatorward shift" in arcs or displays. For the dark months of May and June of 1971, auroral observations at Base General Belgrano (78,0° S; 38,8° W) were used. Four-hourly sequences centered at the break-up (t=0) were studied for the following quantities: a) The magnitude of the interplanetary magnetic field (B), b) The southward component of the interplanetary magnetic field (Bz), c) The solar wind speed (V), d) The solar wind electric field (the westward component: E ), e) The auroral electrojet magnetic activity indices (AE, AL, AU). On the basis of the seven substorms studied, one may deduce that an appreciable increase of geomagnetic activity occured about 40 minutes after the energy arrival at the magnetosphere, but it is not enough strong to take place the break-up, it will happen after another period of 35 minutes. This result confirms that a substorm only occurs after a build-up process. The present paper also confirms the possibility of using the auroral zone geomagnetic activity for estimating the solar wind velocity.En el presente trabajo usamos como indicador de la ruptura de aurora al "sudden equatorward shift" en arcos o displays. Para los meses oscuros de mayo y junio de 1971, se usaron observaciones aurorales en la Base General Belgrano (78,0° S; 38,8° W) Se estudiaron las secuencias de cuatro horas centradas en la ruptura (t=0) para las siguientes variables: a). La amplitud del campo magnético interplanetario (B), b) La componente sur del campo magnético interplanetario (Bz), c) La velocidad del viento solar (V), d) El campo eléctrico del viento solar (la componente oeste: E), c) Los índices de actividad magnética del electrochorro auroral (AE, AL, AU) Sobre la base de las siete subtormentas estudiadas uno puede deducir que ocurrió un incremento apreciable de la actividad geomagnética aproximadamente 40 minutos después de la llegada de la energía a la magnetósfera, pero no han sido lo suficientemente fuertes para tener lugar durante la ruptura, eso sucederá después de otro período de 35 minutos. Este resultado confirma que una sub-tormenta solo ocurre después de un proceso tipo "build-up". El presente trabajo también confirma la posibilidad de usar la actividad geomagnética de la zona auroral para estimar la velocidad del viento solar.Material digitalizado en SEDICI gracias a la colaboración de la Facultad de Ciencias Astronómicas y Geofísicas (UNLP).Asociación Argentina de Geofísicos y Geodesta

Simulación numérica de la distribución de nódulos de manganeso en el fondo del mar

En este trabajo se realiza un desarrollo de cálculo numérico aplicable a la detección de objetos en el fondo sedimentario, el interés del mismo se centra en los yacimientos de nódulos de manganeso. Se emplea el método de simulación numérica que distribuye aleatoriamente áreas representativas en un plano, empleando para ello las distribuciones probabllísticas uniforme y gaussiana. A través de esta descripción analítica, es posible calcular los promedios de masa nodular por unidad de superficie para distintos arreglos y compararlos con los resultados experimentales. Para el caso de yacimientos densamente poblados, se observa la bondad del método.In this paper it is developed a numerical simulation that is applied to determine solid objects in sedimentary floors. The main objective is focused in deposits of manganese nodules. It is used the numerical simulation method that distributes randomly representative areas in a plane, on the basis of the uniform and gaussian probabilistic distribution. Through this analytical description it is possible to calculate the mean of the nodular mass for unit of covered area and for different nodular sets. The analytical results may be compared with experimental ones, showing good agreements in the case of oreshoot.Asociación Argentina de Geofísicos y Geodesta

Simulación numérica de la distribución de nódulos de manganeso en el fondo del mar

En este trabajo se realiza un desarrollo de cálculo numérico aplicable a la detección de objetos en el fondo sedimentario, el interés del mismo se centra en los yacimientos de nódulos de manganeso. Se emplea el método de simulación numérica que distribuye aleatoriamente áreas representativas en un plano, empleando para ello las distribuciones probabllísticas uniforme y gaussiana. A través de esta descripción analítica, es posible calcular los promedios de masa nodular por unidad de superficie para distintos arreglos y compararlos con los resultados experimentales. Para el caso de yacimientos densamente poblados, se observa la bondad del método.In this paper it is developed a numerical simulation that is applied to determine solid objects in sedimentary floors. The main objective is focused in deposits of manganese nodules. It is used the numerical simulation method that distributes randomly representative areas in a plane, on the basis of the uniform and gaussian probabilistic distribution. Through this analytical description it is possible to calculate the mean of the nodular mass for unit of covered area and for different nodular sets. The analytical results may be compared with experimental ones, showing good agreements in the case of oreshoot.Asociación Argentina de Geofísicos y Geodesta

Solar Wind High-Speeds Observed Near the Earth

Abstract. To predict the occurrence of major solar wind velocities near the Earth, hourly solar wind speed magnitudes from November 1963 to May 2000 are considered by applying Gumbel's first distribution. According to the present study a maximum value equal to (1017 ± 50) km/sec is expected to observe during the current solar cycle as a consequence of this result, we infer the possibility to detect intense geomagnetic storms on the Earth

Normal Modes of Black Hole Accretion Disks

This paper studies the hydrodynamical problem of normal modes of small adiabatic oscillations of relativistic barotropic thin accretion disks around black holes (and compact weakly magnetic neutron stars). Employing WKB techniques, we obtain the eigenfrequencies and eigenfunctions of the modes for different values of the mass and angular momentum of the central black hole. We discuss the properties of the various types of modes and examine the role of viscosity, as it appears to render some of the modes unstable to rapid growth

Corotation Resonance and Diskoseismology Modes of Black Hole Accretion Disks

We demonstrate that the corotation resonance affects only some non-axisymmetric g-mode oscillations of thin accretion disks, since it is located within their capture zones. Using a more general (weaker radial WKB approximation) formulation of the governing equations, such g-modes, treated as perfect fluid perturbations, are shown to formally diverge at the position of the corotation resonance. A small amount of viscosity adds a small imaginary part to the eigenfrequency which has been shown to induce a secular instability (mode growth) if it acts hydrodynamically. The g-mode corotation resonance divergence disappears, but the mode magnitude can remain largest at the place of the corotation resonance. For the known g-modes with moderate values of the radial mode number and axial mode number (and any vertical mode number), the corotation resonance lies well outside their trapping region (and inside the innermost stable circular orbit), so the observationally relevant modes are unaffected by the resonance. The axisymmetric g-mode has been seen by Reynolds & Miller in a recent inviscid hydrodynamic accretion disk global numerical simulation. We also point out that the g-mode eigenfrequencies are approximately proportional to m for axial mode numbers |m|>0.Comment: 16 pages, no figures. Submitted to The Astrophysical Journa

On the Energy-Momentum Tensor of the Scalar Field in Scalar--Tensor Theories of Gravity

We study the dynamical description of gravity, the appropriate definition of the scalar field energy-momentum tensor, and the interrelation between them in scalar-tensor theories of gravity. We show that the quantity which one would naively identify as the energy-momentum tensor of the scalar field is not appropriate because it is spoiled by a part of the dynamical description of gravity. A new connection can be defined in terms of which the full dynamical description of gravity is explicit, and the correct scalar field energy-momentum tensor can be immediately identified. Certain inequalities must be imposed on the two free functions (the coupling function and the potential) that define a particular scalar-tensor theory, to ensure that the scalar field energy density never becomes negative. The correct dynamical description leads naturally to the Einstein frame formulation of scalar-tensor gravity which is also studied in detail.Comment: Submitted to Phys. Rev D15, 10 pages. Uses ReVTeX macro

Relativistic Diskoseismology. I. Analytical Results for 'Gravity Modes'

We generalize previous calculations to a fully relativistic treatment of adiabatic oscillations which are trapped in the inner regions of accretion disks by non-Newtonian gravitational effects of a black hole. We employ the Kerr geometry within the scalar potential formalism of Ipser and Lindblom, neglecting the gravitational field of the disk. This approach treats perturbations of arbitrary stationary, axisymmetric, perfect fluid models. It is applied here to thin accretion disks. Approximate analytic eigenfunctions and eigenfrequencies are obtained for the most robust and observable class of modes, which corresponds roughly to the gravity (internal) oscillations of stars. The dependence of the oscillation frequencies on the mass and angular momentum of the black hole is exhibited. These trapped modes do not exist in Newtonian gravity, and thus provide a signature and probe of the strong-field structure of black holes. Our predictions are relevant to observations which could detect modulation of the X-ray luminosity from stellar mass black holes in our galaxy and the UV and optical luminosity from supermassive black holes in active galactic nuclei.Comment: 31 pages, 6 figures, uses style file aaspp4.sty, prepared with the AAS LATEX macros v4.0, significant revision of earlier submission to include modes with axial index m>