Paper
SIMULATIONS OF THE GEOMAGNETIC FIELD DISTURBANCES CAUSED BY THE TUNGUSKA EVENT 1908
Published 2012 · M. Kuzmicheva, T. Losseva
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Abstract
Introduction: On the 30 of June 1908 the fall of a big meteoroid caused explosion in the atmosphere and vast devastation on the ground. The epicenter of the explosion was located at 61° n al and 102°e l close to the Podkamennaya Tunguska river, so the event was named the Tunguska bolide. After the Tunguska event perturbations of components of the geomagnetic field were detected by the Irkuts’s geophysical observatory. This geomagnetic effect was found out only in the Fifties [1], when processes in the ionosphere had been understood better. The geomagnetic field disturbances, detected in Irkutsk started several minutes after the Tunguska explosion. The Irkutsk’s geophysical observatory itself is located at a distance of almost 1000 km from the epicenter. Origin of local disturbances of the geomagnetic field after the Tunguska event was explained by increased ionization in the E-layer of the ionosphere [1]. Further study of gas dynamics flows in atmospheres in catastrophic events (simulations of the fall SchumakerLevy-9 comet onto the Jupiter in 1994 [2]) showed that generation of gas plume due to explosion heads to large-scale disturbances in the upper atmosphere. Plume, throwing up and then falling down provides increased ionization and its transport [3]. Simulations of gas dynamical flow of the Tunguska event were realized in [4], [5]. Hereafter simulations of conductivities in the atmosphere, disturbed by the plume, electric current systems, induced by its motion and the currents’ magnetic field have been carried out. Based on the proposed model we have managed to explain some of the observational data, obtained in Irkutsk in 1908, and determine azimuth of the trajectory of the Tunguska meteoroid by independent manner which value is in a good agreement with azimuths obtained by others (reviewed in [6]) Atmospheric oscillations: A meteoroid entering the atmosphere forms the hot rarefied channel behind, in which the hydrostatic pressure equilibrium is violated. The gas rushes through this channel up and then moves along ballistic trajectories in the rarefied upper atmosphere. The particles involved in the uplift motion are decelerated, and then the gas plume falls down from the height. Impinging dense layers of the atmosphere the plume gas compresses, its kinetic energy is converted into heat. The hot gas expands, and the scenario repeats. Thus, the bulk of the ejected plume involves into the complex oscillatory motion with a period depending on a height of ejection. Rising up higher 100 km, the mass particles of the plume move ballistically, so a horizontal component of their velocities remains unchanged. A bottom of the hot portion of the plume is capable to give input into increased ionization in the ionosphere. As was shown by gas dynamical simulate ions these gas particles have got ejected from heights of 15-20 km, so they have almost the same horizontal component of speed, when plume is in the rarified upper atmosphere. After fall down and flattening it starts decelerating in horizontal direction. In fig.1 temporal evolution of the plume particles ejected from different heights (the upper panel) and temperature evolution at different heights (the lower panel) are shown.
The Tunguska event 1908 caused geomagnetic disturbances due to increased ionization in the ionosphere, leading to complex oscillatory motions in the atmosphere.
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